1.1.1 History

n-Butyl Acetate, sec-Butyl Acetate, tert-Butyl Acetate, and Isobutyl Acetate were previously collected on charcoal tubes and analyzed following OSHA Method 7 Organic Vapors.¹ Diffusive samplers are becoming more popular for workplace sampling. The Methods Development Team at OSHA Salt Lake Technical Center (SLTC) is in the process of validating diffusive samplers for the top 20 most analyzed organic chemicals at SLTC. Candidates for evaluation in this program are selected based on their frequency of analysis at SLTC. n-Butyl Acetate is the ninth most requested organic chemical for analysis at SLTC and Isobutyl Acetate is ranked 22nd. sec-Butyl Acetate and tert-Butyl Acetate were also evaluated to complete the butyl acetate series of chemicals. Separate test atmospheres were dynamically generated for each of the analytes. This method includes two diffusive samplers, SKC 575-002 Passive Samplers and 3M 3520 OVMs, along with charcoal tubes (SKC lot 2000). All analytes performed well on these media in all the tests.

1.1.2 Toxic effects (This section is for information only and should not be taken as the basis of OSHA policy.)^2,3,4,5

All four of these compounds are eye, skin, and mucous membrane irritants. They can cause headache, drowsiness, and narcosis.

1.1.3 Workplace exposure^6,7,8,9

All four of these compounds are used in paints, lacquers, thinners, nail polish removers, perfumes, inks, vinyl resins, photographic film, safety glass, waxes and camphor. Isobutyl Acetate and n-Butyl Acetate are also used as flavouring agents. tert-Butyl Acetate is used as a gasoline additive.

1.1.4 Physical properties and other descriptive information

n-Butyl Acetate^{10 11}

synonyms:	acetic acid, butyl ester; 1-butyl acetate; butyl ethanoate
IMIS:12	0440
CAS number:	123-86-4
boiling point:	125-126 ºC (257-259 ºF)
melting point:	-77 ºC (-106.2 ºF)
density:	0.8826 (g/mL@ 20/20)
molecular weight:	116.16
vapor pressure:	1.33 kPa @20 ºC
flash point:	22 ºC (72 ºF) (closed cup)
appearance:	clear liquid
vapor density:	4 (air = 1)
molecular formula:	C6H12O2
odor:	fruity
solubility:	120 parts water at 25 ºC; misc with alcohol, ether; soluble in most hydrocarbons
autoignition temperature:	421 ºC (790 ºF)
structural formula:

sec-Butyl Acetate13,14
synonyms:	acetic acid, 1-methylpropyl ester; acetic acid, sec-butyl ester; 2-butanol acetate; 1-methylpropyl acetate
IMIS:15	0441
CAS number:	105-46-4
boiling point:	112-113 ºC (234-235 ºF)
melting point:	-98.4 ºC (-145.1 ºF)
density:	0.8748 (g/mL) (20/20)
molecular weight:	116.16
vapor pressure:	1.33 kPa @ 20 ºC
flash point:	16.67 ºC (62 ºF) (closed cup); 31.1 ºC (88 ºF) (open cup)
appearance:	colorless liquid
vapor density:	4 (air = 1)
molecular formula:	C6H12O2
odor:	fruity
solubility:	practically insoluble in water; miscible with common industrial solvents
autoignition temperature:	390 ºC (734 ºF)
structural formula:

tert-Butyl Acetate16, 17
synonyms:	acetic acid, 1,1-dimethylethyl ester; acetic acid, tert-butyl ester; 1,1-dimethylethyl acetate
IMIS:18	0442
CAS number:	540-88-5
boiling point:	97.8 ºC (208 ºF)
melting point:	-62 ºC (-80 ºF)
density:	0.8593 (g/mL) (25/4)
molecular weight:	116.16
vapor pressure:	6.3 kPa @ 25 ºC
flash point:	4.4 ºC (40 ºF) (closed cup)
appearance:	colorless liquid
vapor density:	4 (air = 1)
molecular formula:	C6H12O2
odor:	musty ester odor
solubility:	insoluble in water; miscible with most industrial solvents
autoignition temperature:	518 ºC (964 ºF)
structural formula:

Isobutyl Acetate19,20
synonyms:	acetic acid, isobutyl ester; acetic acid, 2-methylpropyl ester; 2 methylpropyl acetate
IMIS:21	1534
CAS number:	110-19-0
boiling point:	116.5 ºC (242 ºF)
melting point:	-98.8 ºC (-146 ºF)
density:	0.871 (g/mL) (20/20)
molecular weight:	116.16
vapor pressure:	1.73 kPa @ 20 ºC
flash point:	18 ºC (64 ºF) (closed cup)
appearance:	colorless liquid
vapor density:	4 (air = 1)
molecular formula:	C6H12O2
odor:	fruity faintly ester odor
solubility:	very slightly soluble in water; miscible in most organic solvents
autoignition temperature:	422 ºC (793 ºF)
structural formula:

1.2 Limit defining parameters

1.2.1 Detection limit of the analytical procedure

The detection limits of the analytical procedure are 23.5 pg for n-Butyl Acetate, 27.7 pg for sec-Butyl Acetate, 29.7 pg for tert-Butyl Acetate, and 28.0 pg for Isobutyl Acetate. This is the amount of analyte that will give a detector response that is significantly different from the response of a reagent blank. (Section 4.1)

1.2.2 Detection limit of the overall procedure

The detection limits of the overall procedure are listed in Table 1.2.2. These are the amounts of analyte spiked on the respective sampler that will give detector responses that are significantly different from the responses of the respective sampler blanks. (Section 4.2)

Table 1.2.2 Detection Limits of the Overall Procedure

n-Butyl Acetate

sec-Butyl Acetate

tert-Butyl Acetate

Isobutyl Acetate

sampler

μg

ppb

μg/m3

mg

ppb

μg/m3

μg

ppb

μg/m3

μg

ppb

μg/m3

charcoal tube 3M 3520 SKC 575-002

0.62 0.58 0.44

10.9 16.3 29.5

51.7 77.4 140

0.42 0.62 0.37

7.37 19.3 25.5

35.0 91.9 121

0.77 0.87 0.72

13.5 26.4 48.3

64.2 125 229

0.66 0.46 0.66

11.6 13.3 44.0

55.0 63.0 209

1.2.3 Reliable quantitation limit

The reliable quantitation limits are listed in Table 1.2.3. These are the amounts of analyte spiked on the respective samplers that will give detector responses that are considered the lower limits for precise quantitative measurements. (Section 4.2)

1.2.4 Instrument calibration

The standard error of estimate is 301 μg/sample over the range of 2130 to 17100 μg/sample for n-Butyl Acetate. The standard error of estimate is 453 μg/sample over the range of 2850 to 22800 μg/sample for sec-Butyl Acetate. The standard error of estimate is 386 μg/sample over the range of 2850 to 22800 μg/sample for tert-Butyl Acetate. The standard error of estimate is 398 μg/sample over the range of 2130 to 17100 μg/sample for Isobutyl Acetate. This range corresponds to 0.25 to 2 times the TWA target concentration for charcoal tubes. (Section 4.3)

1.2.5 Precision

Charcoal tubes

The precision of the overall procedure at the 95% confidence level for the ambient temperature 17-day storage test for samples collected on charcoal tubes was determined from separate dynamically generated test atmospheres containing each analyte. The test atmospheres were all generated individually for each of the analytes because of possible capacity issues. The concentrations of the atmospheres were 151 ppm (718 mg/m³) n-Butyl Acetate, 198 ppm (941 mg/m³) sec-Butyl Acetate, 202 ppm (960 mg/m³) tert-Butyl Acetate, and 149 ppm (708 mg/m³) Isobutyl Acetate, with an average relative humidity of 80% at 23 °C. The samples were collected at 0.05 L/min. The precisions for charcoal tubes were ± 9.86% for n-Butyl Acetate, ± 9.84% for sec-Butyl Acetate, ± 9.86% tert-Butyl Acetate, and ± 9.92% Isobutyl Acetate. These each include an additional 5% for sampling pump variability. (Section 4.4)

3M 3520 OVMs

The precision of the overall procedure at the 95% confidence level for the ambient temperature 17-day storage test for samples collected on 3M 3520 OVMs was determined from separate dynamically generated test atmospheres containing each analyte. The test atmospheres were all generated individually for each of the analytes because of possible capacity issues. The concentrations of the atmospheres were 151 ppm (718 mg/m³) n-Butyl Acetate, 198 ppm (941 mg/m³) sec-Butyl Acetate, 202 ppm (960 mg/m³) tert-Butyl Acetate, and 149 ppm (708 mg/m³) Isobutyl Acetate, with an average relative humidity of 80% at 23 °C. The precisions are given in Table 1.2.5.1. They each include an additional 6.4% for sampling rate variability. There are different values given, depending on whether both, either, or neither temperature (T) or atmospheric pressure (P) are known at the sampling site. If the sampling site temperature is unknown, it is assumed to be 22.2 ± 15ºC (72 ± 27ºF) and a variability of ±7.7% is included. If the atmospheric pressure is not known, it is estimated from the sampling site elevation and a variability of ±3% is included. (Section 4.4)

Table 1.2.5.1 Precision of the Overall Procedure for 3M 3520 OVMs
	precision (± %)
known conditions	n-Butyl Acetate	sec-Butyl Acetate	tert-Butyl Acetate	Isobutyl Acetate
both T & P only T only P neither T nor P	13.0 14.2 20.0 20.8	13.1 14.3 20.0 20.8	12.9 14.2 19.8 20.8	13.0 14.2 20.0 20.8

SKC 575-002 Passive Samplers

The precision of the overall procedure at the 95% confidence level for the ambient temperature 17-day storage test for samples collected on SKC 575-002 Passive Samplers was determined from separate dynamically generated test atmospheres containing each analyte. The test atmospheres were all generated individually for each of the analytes because of possible capacity issues. The concentrations of the atmospheres were of 151 ppm (718 mg/m³) n-Butyl Acetate, 198 ppm (941 mg/m³) sec-Butyl Acetate, 202 ppm (960 mg/m³) tert-Butyl Acetate and 149 ppm (708 mg/m³) Isobutyl Acetate, with an average relative humidity of 80% at 23 °C. The precisions are given in Table 1.2.5.2. They each include an additional 8.7% for sampling rate variability. There are different values given, depending on whether both, either, or neither temperature (T) or atmospheric pressure (P) are known at the sampling site. If the sampling site temperature is unknown, it is assumed to be 22.2 ± 15ºC (72 ± 27ºF) and a variability of ±7.7% is included. If the atmospheric pressure is not known, it is estimated from the sampling site elevation and a variability of ±3% is included. (Section 4.4)

Table 1.2.5.2 Precision of the Overall Procedure for SKC 575-002
	precision (± %)
known conditions	n-Butyl Acetate	sec-Butyl Acetate	tert-Butyl Acetate	Isobutyl Acetate
both T & P only T only P neither T nor P	17.4 18.4 23.1 23.7	17.4 18.4 23.1 23.7	17.5 18.4 23.1 23.9	17.4 18.4 23.1 23.7

1.2.6 Recovery

The recoveries of n-Butyl Acetate, sec-Butyl Acetate, tert-Butyl Acetate and Isobutyl Acetate from samples used in a 17-day ambient (23ºC) storage test are shown in Table 1.2.6. (Section 4.5)

Table 1.2.6 Recovery of Storage Test
	precision (± %)
sampler	n-Butyl Acetate	sec-Butyl Acetate	tert-Butyl Acetate	Isobutyl Acetate
charcoal tubes 3M 3520 OVM SKC 575-002	96.0 96.3 96.6	98.3 96.1 96.9	97.8 95.9 96.4	96.7 96.6 96.5

1.2.7 Reproducibility

Six samples for each of the three types of samplers and four different analytes were collected separately from individual controlled test atmospheres, and submitted for analysis by the OSHA Salt Lake Technical Center. The samples were analyzed according to a draft copy of this procedure after being stored at 4 ºC for 5 days for n-Butyl Acetate and Isobutyl Acetate and 19 days for sec-Butyl Acetate and tert-Butyl Acetate. No individual sample result deviated from its theoretical value by more than the precision reported in Section 1.2.5. (Section 4.6)

2.1 Apparatus

Charcoal Tubes

Samples are collected using a personal sampling pump calibrated, with the sampling device attached, to within ±5% of the recommended flow rate.

Samples are collected with 7-cm × 4-mm i.d. × 7-mm o.d. glass sampling tubes packed with two sections (100/50 mg) of coconut shell charcoal. The sections are held in place with foam plugs and with a glass wool plug at the front. For this evaluation, commercially prepared sampling tubes were purchased from SKC, Inc. (Catalog no. 226-01, lot no. 2000).

3M 3520 OVMs and SKC 575-002 Passive Samplers

Samples are collected with either 3M 3520 OVMs or with SKC 575-002 Passive Samplers. Samplers were purchased from 3M (catalog no. 3520, contains two charcoal adsorbent pads, lot no. 5049-11) or from SKC, Inc. (catalog no. 575-002, contains 500 mg of Anasorb 747, lot no. 3974).

A thermometer and a barometer to determine the sampling site air temperature and atmospheric pressure.

2.2 Reagents

None required

2.3 Technique

2.3.1 Charcoal tubes

Immediately before sampling, break off both ends of the flame-sealed tube to provide an opening approximately half the internal diameter of the tube. Wear eye protection when breaking the tube. Use tube holders to minimize the hazard of broken glass. All tubes should be from the same lot.

The smaller section of the adsorbent tube is used as a back-up and is positioned nearest the sampling pump. Attach the tube holder to the sampling pump so that the adsorbent tube is in an approximately vertical position with the inlet facing down during sampling. Position the sampling pump, tube holder and tubing so they do not impede work performance or safety.

Draw the air to be sampled directly into the inlet of the tube holder. The air being sampled is not to be passed through any hose or tubing before entering the sampling tube.

After sampling for the appropriate time, remove the adsorbent tube and seal it with plastic end caps. Seal each sample end-to-end with a Form OSHA-21 seal as soon as possible.

Submit at least one blank sample with each set of samples. Handle the blank sample in the same manner as the other samples except draw no air through it.

Record sample air volumes (liters), sampling time (minutes), and sampling rate (L/min) for each sample, along with any potential interferences on the Form OSHA-91A.

Submit the samples to the laboratory for analysis as soon as possible after sampling. As a precaution, store the samples at refrigerator temperature if a delay in shipment is unavoidable. Ship any bulk samples separate from the air samples.

2.3.2 3M OVMs (In general, follow the manufacture’s instructions supplied with the samplers.)

The samplers come individually sealed in small metal cans. When ready to begin sampling, remove the plastic lid from the can and lift up on the revealed ring. Pull back on the ring to open the can. Discard the metal top of the can and remove the sampler. (Caution - The sampler begins to sample immediately after the can is unsealed.)

Keep the two closure caps with attached port plugs, cup and PTFE tubes in the can for later use. Close the can with the plastic lid.

Record the start time on the back of the sampler and on Form OSHA-91A.

Attach the sampler to the worker near his/her breathing zone with the white face forward. Assure that the area directly in front of the sampler is unobstructed throughout the sampling period. Do not remove the white film and ring from the sampler until the sampling period is terminated.

At the end of the sampling period, detach the sampler from the worker and remove the white film and retaining ring. Immediately snap a closure cap onto the primary (top) section of the sampler (where the white film and ring were removed). It is critical that this step be done as quickly as possible because the sampling rate is more than five times faster without the white film in place, which can be an important consideration, especially for short-term sampling. Assure that the attached port plugs are placed firmly into the port holes. The white film and ring can be discarded. Record the stop time on the back of the sampler and on the Form OSHA-91A.

The following steps should be performed in a low background area for a set of samplers as soon as possible after sampling.

Ready a blank by removing the white film and ring and attaching the closure cap onto the unused sampler.

For each sampler (one at a time), separate the primary (top) and secondary (bottom) sections of the sampler using the edge of a coin as a pry tool.

Securely snap a cup onto the bottom of the primary section.

Snap a closure cap onto the secondary section of the sampler and assure that the attached port plugs are placed firmly into the port holes.

Return the sampler sections with closure caps and cup in place to the metal can which contains the PTFE tubes (which will be used by the laboratory). Close the can with the plastic lid, and seal it with a Form OSHA-21.

Verify that the sampling times are properly recorded on Form OSHA-91A for each sample. Also, identify blank samples on this form.

Record the room temperature and atmospheric pressure of the sampling site on Form OSHA-91A.

List any compounds that could be considered potential interferences, especially solvents that are being used in the sampling area.

Submit the samples to the laboratory for analysis as soon as possible after sampling. As a precaution, store the samples at refrigerator temperature if a delay in shipment is unavoidable. Ship any bulk samples separate from the air samples.

2.3.3 SKC 575-002 Passive Samplers (In general, follow the manufacturer's instructions.)

Open the top of the aluminum bag and open the closure to remove the sampler from the container, just before sampling is to begin. Caution- The sampler begins to sample immediately after the aluminum bag is opened. Save the O-ring, press-on cover, cover retainer, port plugs and PTFE tube in the aluminum bag for later use.

Record the start time on the sampler label and on Form OSHA-91A.

Attach the sampler to the worker near his/her breathing zone with the perforations in the sampler facing forward. Assure that the area directly in front of the sampler is unobstructed throughout the sampling period.

At the end of the sampling period, immediately detach the sampler from the worker and attach the cover with the O-ring in place onto the sampler using the cover retainer. Visually inspect the O-ring to be sure it is forming a proper seal around the entire circumference of the sampler. Record the stop time on the sampler label and on Form OSHA-91A. Place the sampler in the aluminum bag, close the bag and place a Form OSHA-21 seal over the closure.

The following steps should be performed in a low background area for a set of samplers as soon as possible after sampling. Prepare a blank by removing an unused sampler from its aluminum package and immediately attaching a cover with the O-ring in place. Replace the sampler into the aluminum bag, close the bag, and seal with a Form OSHA 21 over the closure.

Verify that the sampling times are properly recorded on Form OSHA-91A for each sample. Also, identify blank samples on this form.

Record the room temperature and atmospheric pressure of the sampling site on the Form OSHA-91A.

List any compounds that could be considered potential interferences, especially solvents, which are being used in the sampling area.

Submit the samples to the laboratory for analysis as soon as possible after sampling. As a precaution, store the samples at refrigerator temperature if a delay in shipment is unavoidable. Include all port plugs and PTFE tubes which will be used by the laboratory for analyses. Ship any bulk sample(s) in a container separate from the air samples.

2.4 Sampler capacity (Section 4.7)

2.4.1 Charcoal tubes

The sampling capacity of charcoal tubes was determined using test atmospheres containing the analyte. The test atmospheres were all generated individually for each of the analytes because of possible capacity issues. The concentrations of the test atmospheres were: n-Butyl Acetate (1435 mg/m³ or 302 ppm), sec-Butyl Acetate (1910 mg/m³ or 402 ppm), tert-Butyl Acetate (1930 mg/m³ or 406 ppm), and Isobutyl Acetate (1416 mg/m³ or 298 ppm) with an average relative humidity of 80% at 23ºC. The samples were collected at 0.05 L/min. The 5% breakthrough air volumes at 80% RH and 23ºC were determined to be 25.0 L for n-Butyl Acetate, 17.1 L for sec-Butyl Acetate, 18.1 L for tert-Butyl Acetate, and 25.2 L for Isobutyl Acetate.

2.4.2 3M 3520 OVMs and SKC 575-002 Passive Samplers

The sampling rate and capacity of the 3M 3520 OVMs and the SKC 575-002 Passive Samplers were determined by using test atmospheres containing the analyte. The test atmospheres were all generated individually for each of the analytes because of possible capacity issues. The concentrations of the test atmospheres were: n-Butyl Acetate (1449 mg/m³ or 305 ppm), sec-Butyl Acetate (1892 mg/m³ or 398 ppm), tert-Butyl Acetate (1925 mg/m³ or 405 ppm), and Isobutyl Acetate (1430 mg/m³ or 301 ppm), with an average relative humidity of 80% at 23ºC. Samples were collected for increasing time intervals. Sampler capacity is exceeded when the sampling rate decreases (greater than 4.8 hours for tert-Butyl Acetate, and greater than 6.4 hours for n-Butyl Acetate, sec-Butyl Acetate, and Isobutyl Acetate on both 3M 3520 OVMs and SKC 757-002 Passive Samplers). The average sampling rates on 3M 3520 OVMs were determined to be 31.19 mL/min for n-Butyl Acetate, 28.11 mL/min for sec-Butyl Acetate, 28.94 mL/min for tert-Butyl Acetate, and 30.43 mL/min for Isobutyl Acetate. The average sampling rates on SKC 575-002 Passive Samplers were determined to be 13.07 mL/min for n-Butyl Acetate, 12.74 mL/min for sec-Butyl Acetate, 13.09 mL/min for tert-Butyl Acetate, and 13.16 mL/min for Isobutyl Acetate. The recommended sampling times for this method are 15 minutes for STEL, and 240 minutes for TWA sampling.

2.5 Extraction efficiency (Section 4.8)

It is the responsibility of each analytical laboratory to determine the extraction efficiency of the analyte from the media because the adsorbent material, internal standard, reagents and laboratory techniques may be different than those listed in this evaluation and influence the results.

2.5.1 Charcoal tubes

The mean extraction efficiencies from dry charcoal tubes over the range of RQL to 2 times the target concentration were: 99.3% for n-Butyl Acetate (0.002 to 17.1 mg/sample), 99.2% for sec-Butyl Acetate (0.001 to 23.0 mg/sample), 99.3% for tert-Butyl Acetate (0.003 to 22.7 mg/sample), and 99.1% for Isobutyl Acetate (0.002 to 17.2 mg/sample). The extraction efficiency was not affected by the presence of water.

Extracted samples remain stable for at least 24 h.

2.5.2 3M 3520 OVMs

The mean extraction efficiencies from dry 3M 3520 OVMs over the range of RQL to 2 times the target concentration were: 98.9% for n-Butyl Acetate (0.002 to 10.8 mg/sample), 99.1% for sec-Butyl Acetate (0.002 to 14.4 mg/sample), 99.0% for tert-Butyl Acetate (0.003 to 14.4 mg/sample), and 99.2% for Isobutyl Acetate (0.002 to 10.8 mg/sample). The extraction efficiency was not affected by the presence of water.

Extracted samples remain stable for at least 24 h.

2.5.3 SKC 575-002 Passive Samplers

The mean extraction efficiencies from dry SKC 575-002 Passive Samplers over the range of RQL to 2 times the target concentration were: 99.2% for n-Butyl Acetate (0.002 to 4.41 mg/sample), 99.1% for sec-Butyl Acetate (0.001 to 5.88 mg/sample), 98.9% for tert-Butyl Acetate (0.002 to 5.88 mg/sample), and 99.1% for Isobutyl Acetate (0.002 to 4.42 mg/sample). The extraction efficiency was not affected by the presence of water.

Extracted samples remain stable for at least 24 h.

2.6 Recommended sampling time and sampling rate

2.6.1 Charcoal tubes

Sample with charcoal tubes for up to 240 min at 0.05 L/min (12 L) to collect TWA (long-term) samples, and for 15 min at 0.05 L/min (0.75 L) to collect short-term samples.

When short-term samples are collected, the air concentration equivalent to the reliable quantitation limit becomes larger. For example, the reliable quantitation limits for charcoal tubes are 0.59 ppm (2.8 mg/m³) for n-Butyl Acetate, 0.39 ppm (1.9 mg/m³) for sec-Butyl Acetate, 0.73 ppm (3.5 mg/m³) for tert-Butyl Acetate, and 0.62 ppm (2.9 mg/m³) for Isobutyl Acetate when 0.75 L are collected.

2.6.2 3M 3520 OVMs

Sample with 3M 3520 OVMs for up to 240 min to collect TWA (long-term) samples, and for 15 min to collect short-term samples. The sampling rates are 31.19 mL/min for n-Butyl Acetate, 28.11 mL/min for sec-Butyl Acetate, 28.94 mL/min for tert-Butyl Acetate, and 30.43 mL/min for Isobutyl Acetate.

When short-term samples are collected, the air concentration equivalent to the reliable quantitation limit becomes larger. For example, the reliable quantitation limits for 3M 3520 OVMs are 0.85 ppm (4.0 mg/m³) for n-Butyl Acetate with an air volume of 0.47 L (15 min x 31.19 mL/min), 1.1 ppm (5.0 mg/m³) for sec-Butyl Acetate with 0.42 L (15 min x 28.11 mL/min), 1.4 ppm (6.7 mg/m³) for tert-Butyl Acetate with 0.43 L (15 min x 28.94 mL/min), and 0.69 ppm (3.3 mg/m³) for Isobutyl Acetate with 0.46 L (15 min x 30.43 mL/min) collected.

2.6.3 SKC 575-002 Passive Samplers

Sample with SKC 575-002 Passive Samplers for up to 240 min to collect TWA (long-term) samples, and for 15 min to collect short-term samples. The sampling rates are 13.07 mL/min for n-Butyl Acetate, 12.74 mL/min for sec-Butyl Acetate, 13.09 mL/min for tert-Butyl Acetate, and 13.16 mL/min for Isobutyl Acetate.

When short-term samples are collected, the air concentration equivalent to the reliable quantitation limit becomes larger. For example, the reliable quantitation limits for SKC 575-002 Passive Samplers are 1.6 ppm (7.5 mg/m³) for n-Butyl Acetate with an air volume of 0.20 L (15 min x 13.07 mL/min), 1.3 ppm (6.3 mg/m³) for sec-Butyl Acetate with 0.19 L (15 min x 12.74 mL/min), 2.5 ppm (12 mg/m³) for tert-Butyl Acetate with 0.20 L (15 min x 13.09 mL/min), and 2.3 ppm (11 mg/m³) for Isobutyl Acetate with 0.20 L (15 min x 13.16 mL/min) collected.

2.7 Interferences, sampling (Section 4.9)

2.7.1 Charcoal tubes

Retention

The mean retention efficiency was 99.8% for n-Butyl Acetate, 99.9% for sec-Butyl Acetate, 100.4% for tert-Butyl Acetate, and 100.3% for Isobutyl Acetate, when charcoal tubes containing 4300 μg of n-Butyl Acetate, 5730 μg of sec-Butyl Acetate, 5780 μg of tert-Butyl Acetate, and 4250 μg of Isobutyl Acetate were allowed to sample 9 L of contaminant-free air having an average relative humidity of 80% at 23ºC. (Section 4.9.1)

Low humidity

The ability of charcoal tubes to collect the analytes from a relatively dry atmosphere was determined by sampling an atmosphere containing two times the target concentration and approximately 20% RH at 23ºC. Separate test atmospheres were dynamically generated for each of the analytes. The mean recoveries (% of theoretical) were: 99.4% for n-Butyl Acetate, 99.4% for sec-Butyl Acetate, 99.5% for tert-Butyl Acetate, and 99.4% for Isobutyl Acetate. (Section 4.9.1)

Low concentration

The ability of charcoal tubes to collect the analytes at low concentrations was tested by sampling an atmosphere at 0.1 times the target concentration with approximately 80% RH at 23ºC. Separate test atmospheres were dynamically generated for each of the analytes. The mean recoveries (% of theoretical) were: 99.8% for n-Butyl Acetate, 99.1% for sec-Butyl Acetate, 99.1% for tert-Butyl Acetate, and 100.1% for Isobutyl Acetate. (Section 4.9.1)

Sampling interference

The ability of charcoal tubes to collect the analyte when other potential interferences are present was tested by sampling individual atmospheres containing a given analyte and an interference mixture of n-butyl alcohol, hexone, and toluene at an average humidity of 80% at 23ºC. Separate test atmospheres were dynamically generated for each of the analytes with these interferences. The concentrations of the analytes in the four individual test atmospheres were: n-Butyl Acetate (718 mg/m³ or 151 ppm), sec-Butyl Acetate (955 mg/m³ or 201 ppm), tert-Butyl Acetate (965 mg/m³ or 203 ppm), and Isobutyl Acetate (708 mg/m³ or 149 ppm). Each test atmosphere also had the following concentrations of the interference mixture in it: n-butyl alcohol (302 mg/m³ or 101 ppm), hexone (408 mg/m³ or 99 ppm), and toluene (375 mg/m³ or 100 ppm). Three samplers had contaminated air drawn through them at 0.05 L/min for 240 min for each test. All of the samples were immediately analyzed. The mean recoveries (% of theoretical) were: n-Butyl Acetate 99.0%, sec-Butyl Acetate 99.7%, tert-Butyl Acetate 99.2%, and Isobutyl Acetate 99.5%. There was no analyte on the backup portion of the charcoal tubes for any of the tests.

A test of the ability of the sampler to collect all four analytes from the same test atmosphere was performed by creating a test atmosphere at the PEL level of all four analytes in humid air having an average relative humidity of 80% at 22 °C. The concentrations of the test atmospheres were: n-Butyl Acetate (718 mg/m³ or 151 ppm), sec-Butyl Acetate (955 mg/m³ or 201 ppm), tert-Butyl Acetate (965 mg/m³ or 203 ppm), and Isobutyl Acetate (708 mg/m³ or 149 ppm). Due to concerns about the capacity of the media to collect all four analytes at these concentrations without breakthrough, three charcoal tubes were collected at 0.05 L/min for 2 hours instead of the 4 hours listed in "Evaluation Guidelines for Air Sampling Methods Utilizing Chromatographic Analysis".²³ The recoveries (% of theoretical) were: 101.1%, 99.7%, and 98.1% for n-Butyl Acetate; 100.3%, 99.3%, and 97.1% for sec-Butyl Acetate; 101.7%, 99.5%, and 98.4% for tert-Butyl Acetate; and 101.5%, 99.5%, and 97.8% for Isobutyl Acetate. There was no analyte on the backup section of the charcoal tubes for any of the tests. (Section 4.9.1)

2.7.2 3M 3520 OVMs

Reverse diffusion

Reverse diffusion is a measure of the ability of the sorbent within a diffusive sampler to retain the analyte collected. Reverse diffusion is measured by first exposing two sets of samplers to humid air containing the analyte, and then additionally exposing one of the sets to clean humid air of an average relative humidity of 80% at 23ºC. Separate test atmospheres were dynamically generated for each analyte. Comparison of the two sets of 3M 3520 OVMs showed that an average recovery of 99.3% for n-Butyl Acetate, 97.8% for sec-Butyl Acetate, 98.0% for tert-Butyl Acetate, and 100.4% for Isobutyl Acetate was retained. (Section 4.9.2)

Low humidity

The ability of 3M 3520 OVMs to collect the analyte from a relatively dry atmosphere was determined by sampling an atmosphere containing two times the target concentration and an average relative humidity of approximately 20% at 23ºC. Separate test atmospheres were dynamically generated for each of the analytes. The mean recoveries (% of theoretical) were: n-Butyl Acetate 99.8%, sec-Butyl Acetate 99.6%, tert-Butyl Acetate 98.4%, and Isobutyl Acetate 99.9%. (Section 4.9.2)

Low concentration

The ability of 3M 3520 OVMs to collect the analytes at low concentration was determined by sampling a test atmosphere containing 0.1 times the target concentration of the analyte in an atmosphere at approximately 80% RH at 23ºC. Separate test atmospheres were dynamically generated for each of the analytes. The mean recoveries (% of theoretical) were: were n-Butyl Acetate 98.6%, sec-Butyl Acetate 98.8%, tert-Butyl Acetate 97.7%, and Isobutyl Acetate 99.0%. (Section 4.9.2)

Sampling interference

The ability of 3M 3520 OVMs to collect the analyte when other potential interferences are present was tested by sampling individual atmospheres containing a given analyte and an interference mixture of n-butyl alcohol, hexone, and toluene at an average humidity of 80% at 23ºC. Separate test atmospheres were dynamically generated for each of the analytes with these interferences. The concentrations of the analytes in the four individual test atmospheres were: n-Butyl Acetate (718 mg/m³ or 151 ppm), sec-Butyl Acetate (955 mg/m³ or 201 ppm), tert-Butyl Acetate (965 mg/m³ or 203 ppm), and Isobutyl Acetate (708 mg/m³ or 149 ppm). Each test atmosphere also had the following concentrations of the interference mixture in it: n-butyl alcohol (302 mg/m³ or 101 ppm), hexone (408 mg/m³ or 99 ppm), and toluene (375 mg/m³ or 100 ppm). Three samplers were exposed for 240 min in each test. All of the samples were immediately analyzed. The mean recoveries (% of theoretical) were: n-Butyl Acetate 100.3%, sec-Butyl Acetate 101.0%, tert butyl acetate 100.1%, and Isobutyl Acetate 99.5%. There was no analyte on the backup pad of the sampler for any of the tests.

A test of the ability of the sampler to collect all four analytes from the same test atmosphere was performed by creating a test atmosphere at the PEL level of all four analytes in humid air having an average relative humidity of 80% at 22 °C. The concentrations of the test atmospheres were: n-Butyl Acetate (718 mg/m³ or 151 ppm), sec-Butyl Acetate (955 mg/m³ or 201 ppm), tert-Butyl Acetate (965 mg/m³ or 203 ppm), and Isobutyl Acetate (708 mg/m³ or 149 ppm). Due to concerns about the capacity of the media to collect all four analytes at these concentrations, three 3M 3520 OVMs were collected for 2 hours instead of the 4 hours listed in "Evaluation Guidelines For Air Sampling Methods Utilizing Chromatographic Analysis".²⁴ The recoveries (% of theoretical) were: 100.2%, 99.1%, and 96.9% for n-Butyl Acetate; 100.8%, 99.6%, and 98.2% for sec-Butyl Acetate; 101.1%, 99.7%, and 98.1% for tert-Butyl Acetate; and 100.6%, 99.1%, and 98.0% for Isobutyl Acetate. There was no analyte on the backup pad of the sampler for any of the tests. This test also shows that the presence of all four analytes had no significant effect on the sampling rate for any of the individual analytes. (Section 4.9.2)

2.7.3 SKC 575-002 Passive Samplers

Reverse diffusion

Reverse diffusion is a measure of the ability of the sorbent within a diffusive sampler to retain the analyte collected. Reverse diffusion is measured by first exposing two sets of samplers to humid air containing the analyte, and then additionally exposing one of the sets to clean humid air of an average relative humidity of 80% at 23ºC. Separate test atmospheres were dynamically generated for each of the analytes. Comparison of the two sets of SKC 575-002 Passive Samplers showed that an average recovery of 100.4% for n-Butyl Acetate, 98.0% for sec-Butyl Acetate, 97.4% for tert-Butyl Acetate, and 99.1% for Isobutyl Acetate was retained. (Section 4.9.3)

Low humidity

The ability of SKC 575-002 Passive Samplers to collect the analyte from a relatively dry atmosphere was determined by sampling an atmosphere containing two times the target concentration and an average relative humidity of approximately 20% at 23ºC. Separate test atmospheres were dynamically generated for each of the analytes. The mean recoveries (% of theoretical) were: n-Butyl Acetate 99.9%, sec-Butyl Acetate 100.6%, tert-Butyl Acetate 100.4%, and Isobutyl Acetate 100.5%. (Section 4.9.3)

Low concentration

The ability of SKC 575-002 Passive Samplers to collect the analytes at low concentration was tested by creating separate test atmospheres containing 0.1 times the target concentration of the analyte at approximately 80% RH at 23ºC. The mean recoveries (% of theoretical) were: n-Butyl Acetate 98.1%, sec-Butyl Acetate 97.3%, tert-Butyl Acetate 98.5%, and Isobutyl Acetate 98.3%. (Section 4.9.3)

Sampling interference

The ability of SKC 575-002 Passive Samplers to collect the analyte when other potential interferences are present was tested by sampling individual atmospheres containing a given analyte and an interference mixture of n-butyl alcohol, hexone, and toluene at an average humidity of 80% at 23ºC. Separate test atmospheres were dynamically generated for each of the analytes with these interferences. The concentrations of the analytes in the four individual test atmospheres were: n-Butyl Acetate (718 mg/m³ or 151 ppm), sec-Butyl Acetate (955 mg/m³ or 201 ppm), tert-Butyl Acetate (965 mg/m³ or 203 ppm), and Isobutyl Acetate (708 mg/m³ or 149 ppm). Each test atmosphere also had the following concentrations of the interference mixture in it: n-butyl alcohol (302 mg/m³ or 101 ppm), hexone (408 mg/m³ or 99 ppm), and toluene (375 mg/m³ or 100 ppm). Three samplers were exposed for 240 min in each test. All of the samples were immediately analyzed. The mean recoveries (% of theoretical) were: n-Butyl Acetate 101.3%, sec-Butyl Acetate 100.5%, tert butyl acetate 100.3%, and Isobutyl Acetate 99.7%.

A test of the ability of the sampler to collect all four analytes from the same test atmosphere was performed by creating a test atmosphere at the PEL level of all four analytes in humid air having an average relative humidity of 80% at 22 °C. The concentrations of the test atmospheres were: n-Butyl Acetate (718 mg/m³ or 151 ppm), sec-Butyl Acetate (955 mg/m³ or 201 ppm), tert-Butyl Acetate (965 mg/m³ or 203 ppm), and Isobutyl Acetate (708mg/m³ or 149 ppm). Due to concerns about the capacity of the media to collect all four analytes at these concentrations, three SKC 575-002 Passive Samplers were collected for 2 hours instead of the 4 hours listed in "Evaluation Guidelines For Air Sampling Methods Utilizing Chromatographic Analysis".²⁵ The recoveries (% of theoretical) were: 102.1%, 99.4%, and 97.6% for n-Butyl Acetate; 101.0%, 99.6%, and 98.3% for sec-Butyl Acetate; 100.4%, 99.1%, and 96.8% for tert-Butyl Acetate; and 100.8%, 99.3%, and 97.6% for Isobutyl Acetate. This test also shows that the presence of all four analytes had no significant effect on the sampling rate for any of the individual analytes. (Section 4.9.3)

3.1 Apparatus

Gas chromatograph equipped with an FID. A Hewlett-Packard Model 6890 GC equipped with an integrator, an automatic sample injector, and an FID was used in this evaluation.

A GC column capable of separating n-Butyl Acetate, sec-Butyl Acetate, tert-Butyl Acetate, and Isobutyl Acetate from the extracting solvent, poterntial interferences, and internal standard. A Restek 60-m × 0.32-mm i.d. Stabilwax (1-μm df) capillary column was used in this evaluation.

An electronic integrator or other suitable means of measuring GC detector response. A Waters Empower 2 Data System, along with a Hewlett Packard 3396 Series II integrator were used in this evaluation.

Glass vials with PTFE-lined caps. For this evaluation 2 and 4-mL vials were used.

A dispenser capable of delivering 1.0 or 2.0 mL of extracting solvent to prepare standards and samples. If a dispenser is not available, 1.0- and 2.0-mL volumetric pipets can be used.

Class A volumetric flasks - 10-mL and other convenient sizes for preparing standards.

Calibrated 10-μL syringe for preparing standards.

An SKC Desorption shaker with rack (226D-03K) was used to extract SKC 575-002 Passive Samplers in this evaluation.

A mechanical shaker. An Eberbach mechanical shaker was used to extract the charcoal tubes and 3M pads in this evaluation.

3.2 Reagents

n-Butyl Acetate, [CAS no. 123-86-4], reagent grade or better. The n-Butyl Acetate used in this evaluation was 99.5+% (lot no. 00262DC) purchased from Sigma-Aldrich (Milwaukee, WI).

sec-Butyl Acetate, [CAS no. 105-46-4], reagent grade or better. The sec-Butyl Acetate used in this evaluation was 99% (lot no. 12930HD) purchased from Aldrich (Milwaukee, WI).

tert-Butyl Acetate, [CAS no. 540-88-5], reagent grade or better. The tert-Butyl Acetate used in this evaluation was 99+% (lot no. 17531AB) purchased from Aldrich (Milwaukee, WI).

Isobutyl Acetate, [CAS no. 110-19-0], reagent grade or better. The Isobutyl Acetate used in this evaluation was 99+% (lot no. 00262DC) purchased from Sigma-Aldrich (Milwaukee, WI).

Carbon disulfide (CS₂), [CAS no. 75-15-0], reagent grade or better. The carbon disulfide used in this evaluation was 99.9+% low benzene content grade (lot no. 11561HC) purchased from Aldrich (Milwaukee, WI).

n-Hexyl benzene [CAS no. 1077-16-3], reagent grade or better. The n-hexyl benzene (listed as 1-phenyl hexane on the bottle) used in this evaluation was 97% (lot no. 06202KO) purchased from Aldrich (Milwaukee, WI).

The extraction solvent used for this evaluation consisted of 0.25 μL/mL n hexyl benzene in the CS₂. The n hexyl benzene was added to CS₂ as an internal standard. Other internal standards can be used provided they are fully tested.

3.3 Standard preparation

Charcoal tubes are extracted with 1 mL of extraction solvent. Prepare analytical standards for each of the analytes by injection of microliter amounts of the analytes into 1-mL volumetric flasks and diluting with the extraction solvent over a concentration range of 0.002 to 23 mg/mL. For example: a target concentration standard for n-Butyl Acetate was prepared by injecting 10 μL of n-Butyl Acetate into a 1-mL volumetric flask containing about 0.75 mL of extracting solvent and then diluting to the mark with extraction solvent (8.83 mg/mL, or 155 ppm based on a 1-mL extraction and 12 L air volume) Similarly the other analytes would be prepared as follows: for 200 ppm sec-Butyl Acetate use 13 μL/mL (11.4 mg/mL), for 196 ppm tert-Butyl Acetate use 13 μL/mL (11.2 mg/mL), and for 153 ppm Isobutyl Acetate use 10 μL/mL (8.71 mg/mL).

The diffusive samplers are extracted into 2 mL of the extraction solvent. Prepare analytical standards for each of the analytes by injection of microliter amounts of the analytes into 2-mL volumetric flasks and diluting with extraction solvent. For example: a target concentration level (for 3M 3520 OVM) standard for n-Butyl Acetate was prepared by injecting 6 μL of n-Butyl Acetate into a 2-mL volumetric flask containing about 1.75 mL extraction solvent and then diluting to the mark with extraction solvent (5.30 mg/2 mL or 2.65 mg/mL).

Bracket sample concentrations with standard concentrations. If upon analysis, sample concentrations fall outside the range of prepared standards, prepare and analyze additional standards to confirm instrument response, or dilute high samples with extraction solvent and reanalyze the diluted samples.

3.4 Sample preparation

3.4.1 Charcoal tubes

Remove the plastic end caps from the sample tube and carefully transfer each section of the adsorbent to separate 2-mL vials. Discard the glass tube and glass wool and polyurethane plugs.

Add 1.0 mL of extracting solution to each vial and immediately seal the vials with PTFE-lined caps.

Shake the vials on a shaker for 30 min (Shaking is necessary to obtain the extraction efficiency found in this method; without shaking the extraction efficiencies will be lower.)

3.4.2 3M 3520 OVMs (In general, follow the manufacturer's instructions.)

Remove both sampler sections from the metal can, along with the sections of PTFE tubing. Assure that the closure caps are firmly snapped to the primary and secondary sections of all the samplers, that all cap plugs are firmly seated in the cap ports, and that the bottom closure cup for the secondary section is firmly in place. Any deviations must be noted. Make sure each section of the sampler is labeled properly for future reference.

Prepare one section of the sampler at a time by temporarily removing the cap plugs from the ports and pipeting 2.0 mL of extraction solvent through the center port. Immediately replace the plugs in the ports. Repeat the process for the second section.

Allow the sampler sections to extract for 30 min. Periodically apply gentle agitation to the sampler sections during the extraction period.

Do not leave the extracted sample in the sampler. Transfer the solution from each sampler section by removing both plugs from the ports, inserting a decanting spout (a small section of PTFE tubing) into the rim port and pouring the liquid through the spout into a labeled 2-mL autosampler vial. Immediately cap each vial.

An alternate means of extraction for the 3M 3520 OVMs is to remove the cap, pull off the interior retaining ring, remove the charcoal pad, and place the pad into a labeled 4-mL vial. Remove the pad from the second section of the sampler in similar fashion. Add 2-mL of the extraction solvent to each vial and cap the vial. Shake the vial occasionally by hand over the next 30 minutes (at least 5 times), or shake on a shaker for 30 min. Transfer the sample into a labeled 2-mL autosampler vial. Immediately cap each vial.

Extraction studies at the PEL level showed similar extraction efficiencies whether the samples were extracted inside the sampler, or with the charcoal pad removed and extracted in a 4-mL vial (Table 4.8.2.5). The 3M 3520 OVM consists of two sections which are separated after sampling. A bottom closure cap is then placed on the top section and top caps on both sections. It was often difficult to get the bottom closure cap seated properly on the top section of the 3M 3520 OVM. If the bottom closure cap was not seated properly, the extraction solvent would leak out through any open space. Most of the samples extracted in this method were by the second, alternate, extraction method, with each pad removed from the sampler, and placed into separate labeled 4-mL vials for extraction.

3.4.3 SKC 575-002 Passive Samplers (In general, follow the manufacturer's instructions.)

Cut off the ends of the two protruding tubes of each sampler with scissors, razor blade, or sharp knife.

Slowly pipet 2.0 mL of extraction solvent through one of the protruding tubes (ports), stopping at least once to allow the bubbling to subside before adding the rest of the extraction solvent.

Immediately insert plugs into the ports.

Mount the samplers in the sampler rack of a specialized shaker (SKC Cat. No. 226D-03K) and shake the samplers for 1 hour.

Do not leave the extracted sample in the sampler. Transfer each extracted sample by removing the plugs from the sampler ports, firmly inserting the tapered end of a supplied PTFE tube into the outer port and carefully pouring the solution through the PTFE tube into a labeled autosampler vial. Immediately cap each vial.

3.5 Analysis

3.5.1 Gas chromatography conditions:

Zone temperatures:
column:	initial 50 ºC, hold 4 min, program at 10 ºC/min to 170 ºC, hold 4 min
injector:	250 ºC
detector:	260 ºC
run time:	20 min
column gas flow:	1.5 mL/min (hydrogen)
injection size:	1.0 µL (10:1 split)
column:	60-m × 0.32 mm i.d. Stabilwax capillary column (df = 1 μm)
retention times:	carbon disulfide 4.86 min, tert-Butyl Acetate 7.58 min, sec-Butyl Acetate 9.29 min, Isobutyl Acetate 9.81 min, n-Butyl Acetate 10.9 min, and n-hexyl benzene 18.6 min
FID conditions:
hydrogen flow:	30 mL/min
air flow:	400 mL/min
nitrogen makeup flow:	20 mL/min
Peak areas are measured with an integrator or other suitable means.
	Figure 3.5.1. A chromatogram of 8.83 mg/mL n-Butyl Acetate, 8.71 mg/mL Isobutyl Acetate, 11.4 mg/mL sec-Butyl Acetate, 11.2 mg/mL tert-Butyl Acetate in the extraction solution. (Key: (1) CS2; (2) tert-Butyl Acetate; (3) sec-Butyl Acetate; (4) Isobutyl Acetate; (5) n-Butyl Acetate; and (6) n-hexyl benzene (ISTD))

3.5.2 An internal standard (ISTD) calibration method is used. A calibration curve can be constructed by plotting response of standard injections versus micrograms of analyte per sample. Bracket the samples with freshly prepared analytical standards over the range of concentrations.

Figure 3.5.2.1. Calibration curve for n-Butyl Acetate. (y = 162x – 3.97E4)		Figure 3.5.2.2. Calibration curve for sec-Butyl Acetate. (y = 156x – 6.13E4)
Figure 3.5.2.3. Calibration curve for tert-Butyl Acetate. (y = 158x – 5.29E4)		Figure 3.5.2.4. Calibration curve for Isobutyl Acetate. (y = 166x - 5.60E4)

Any compound that produces a GC response and has a similar retention time as the analyte is a potential interference. If any potential interferences were reported, they should be considered before samples are extracted. Generally, chromatographic conditions can be altered to separate an interference from the analyte.

When necessary, the identity or purity of an analyte peak can be confirmed by GC-mass spectrometry, or by another analytical procedure (Section 4.10)

3.7 Calculations

3.7.1 Charcoal tubes

The amount of analyte per sampler is obtained from the appropriate calibration curve in terms of micrograms per sample, uncorrected for extraction efficiency. The amount found on the back section of the charcoal tube is added to the front section for the total loading on the charcoal tube. The back-up section is analyzed separately to determine the extent of analyte saturation to determine if breakthrough occurred. This total amount is then corrected by subtracting the total amount (if any) found on the blank. The air concentration is calculated using the following formulas.

CM =	M		Where:	CM is concentration by weight (mg/m3) M is micrograms per sample V is liters of air sampled EE is extraction efficiency, in decimal form
	VEE
CV =	VMCM		Where:	CV is concentration by volume (ppm) VM is 24.46 (molar volume at NTP) CM is concentration by weight (mg/m3) Mr is molecular weight of analyte (isomers of n butyl acetate = 116.16)
	Mr

3.7.2 3M 3520 OVMs and SKC 575-002 Passive Samplers

The amount of analyte for the samples is obtained from the appropriate calibration curve in terms of micrograms per sample, uncorrected for extraction efficiency. In the case of the 3M 3520 OVMs, the back section is analyzed primarily to determine the extent of sampler saturation. If any analyte is found on the back section, the amount is multiplied by 2.2 (as per manufacturer’s instructions) and then added to the amount on the front section. The 3M 3520 OVM sampler is deemed saturated when the corrected amount found on the back section is 50% of the amount found on the front section.

The total amount is corrected by subtracting the total amount (if any) found on the blank. The SKC 575-002 Passive samplers have only one section. The total micrograms per sample are the amount found on the sampler minus the amount found on the blank (if any).

Table 3.7.2 Sampling Rates of Diffusive Samplers (mL/min) analyte 3M 3520 OVM SKC 575-002 n-Butyl Acetate sec-Butyl Acetate tert-Butyl Acetate Isobutyl Acetate 31.19 28.11 28.94 30.43 13.07 12.74 13.09 13.16

The air concentration is calculated using the following formulas.

				Where:	RSS is the sampling rate at sampling site TSS is the sampling site temperature in K TNTP is 298.2 K PSS is the sampling site pressure in mmHg PNTP is 760 mmHg RNTP is the sampling rate at NTP conditions
CM	=	M1000		Where:	CM is concentration by weight (mg/m3) M is micrograms per sample RSS is the sampling rate at the sampling site t is the sampling time (min) EE is extraction efficiency, in decimal form
		tRSSEE
CV = VMCM   Mr				Where:	CV is concentration by volume (ppm) VM is molar volume at 25 °C = 24.46 CM is concentration by weight (mg/m3) Mr is molecular weight of analyte (isomers of n butyl acetate = 116.16)

If the sampling site temperature is not provided, assume that it is 22.2ºC. If the sampling site atmospheric pressure is not given, calculate an approximate value based on the sampling site elevation from the following equation.

PSS = AE2 - BE + 760

Where:

PSS is the approximate atmospheric pressure E is the sampling site elevation, ft A is 3.887 10-7 mmHg/ft2 B is 0.02748 mmHg/ft

4.1 Detection limit of the analytical procedure (DLAP)

The DLAP is measured as the mass of analyte introduced onto the chromatographic column. Ten analytical standards were prepared with equally descending increments with the highest standard containing 5.30 μg/mL n-Butyl Acetate, 5.20 μg/mL sec-Butyl Acetate, 5.15 μg/mL tert-Butyl Acetate and 5.20 μg/mL Isobutyl Acetate. These are the concentrations that would produce peaks approximately 10 times the response of a reagent blank near the elution time of the analyte. These standards, and the reagent blank were analyzed with the recommended analytical parameters (1-μL injection with a 1:10 split), and the data obtained were used to determine the required parameters (standard error of estimate and slope) for the calculation of the DLAP. The slope and standard error of estimate, respectively, for n-butyl acetate were 1.88 and 14.67; for sec-Butyl Acetate were 1.73 and 15.99; for tert-Butyl Acetate were 1.57 and 15.52, and Isobutyl Acetate were 1.83 and 17.08. DLAP was calculated to be 23.5 pg for n-Butyl Acetate, 27.7 pg for sec-Butyl Acetate, 29.7 pg for tert-Butyl Acetate, and 28.0 pg for Isobutyl Acetate.

Table 4.1.1 Detection Limit of the Analytical Procedure for n-Butyl Acetate concentration (μg/mL) mass on column (pg) area counts (μV•s) 0 0.53 1.06 1.59 2.12 2.65 3.18 3.71 4.24 4.77 5.30 0 53 106 159 212 265 318 371 424 477 530 0 96 193 266 396 465 587 684 767 887 1004		Figure 4.1.1. Plot of data to determine the DLAP for n-Butyl Acetate. (y = 1.88x – 11.0)
Table 4.1.2 Detection Limit of the Analytical Procedure for sec-Butyl Acetate concentration (μg/mL) mass on column (pg) area counts (μV•s) 0 0.52 1.04 1.56 2.08 2.60 3.12 3.64 4.16 4.68 5.20 0 52 104 156 208 260 312 364 416 468 520 0 98 192 311 367 433 545 634 743 806 919		Figure 4.1.2. Plot of data to determine the DLAP of sec-Butyl Acetate. (y =1.73x + 8.73)
Table 4.1.3 Detection Limit of the Analytical Procedure for tert-Butyl Acetate concentration (μg/mL) mass on column (pg) area counts (μV•s) 0 0.52 1.03 1.55 2.06 2.58 3.09 3.61 4.12 4.64 5.15 0 52 103 155 206 258 309 361 412 464 515 0 91 160 239 331 385 466 537 649 723 830		Figure 4.1.3. Plot of data to determine the DLAP for tert-Butyl Acetate. (y =1.57x – 2.80)
Table 4.1.4 Detection Limit of the Analytical Procedure for Isobutyl Acetate concentration (μg/mL) mass on column (pg) area counts (μV•s) 0 0.52 1.04 1.56 2.08 2.60 3.12 3.64 4.16 4.68 5.20 0 52 104 156 208 260 312 364 416 468 520 0 114 218 306 394 478 573 645 759 871 989		Figure 4.1.4. Plot of data to determine the DLAP for Isobutyl Acetate. (y =1.83x +10.96)

4.2 Detection limit of the overall procedure (DLOP) and reliable quantitation limit (RQL) DLOP is measured as mass per sample and expressed as equivalent air concentrations, based on the recommended sampling parameters. Ten samplers were spiked with equally descending increments of analyte. The highest amount is the amount spiked on the sampler that would produce a peak approximately 10 times the response of a sample blank. These spiked samplers, and the sample blank were analyzed with the recommended analytical parameters, and the data obtained used to calculate the required parameters (standard error of estimate and the slope) for the calculation of the DLOP.

Table 4.2 Detection Limits of the Overall Procedure

sampler

n-Butyl Acetate

sec-Butyl Acetate

tert-Butyl Acetate

Isobutyl Acetate

μg

ppb

μg/m3

μg

ppb

μg/m3

μg

ppb

μg/m3

μg

ppb

μg/m3

charcoal tube 3M 3520 SKC 575-002

0.62 0.58 0.44

10.9 16.3 29.5

51.7 77.4 140

0.42 0.62 0.37

7.37 19.3 25.5

35.0 91.9 121

0.77 0.87 0.72

13.5 26.4 48.3

64.2 125 229

0.66 0.46 0.66

11.6 13.3 44.0

55.0 63.0 209

Table 4.2.1 Detection Limit of the Overall Procedure for n-Butyl Acetate Collected on Charcoal Tubes mass per sample (µg) area counts (µV•s) 0 1.06 2.12 3.18 4.24 5.30 6.36 7.42 8.48 9.54 10.6 0 224 374 618 743 976 1143 1380 1565 1721 1829		Figure 4.2.1. Plot of data to determine the DLOP/RQL for n-Butyl Acetate on charcoal tubes. (y = 177x + 23.5)
Table 4.2.2 Detection Limit of the Overall Procedure for sec-Butyl Acetate Collected on Charcoal Tubes mass per sample (µg) area counts (µV•s) 0 1.04 2.08 3.12 4.16 5.20 6.24 7.28 8.32 9.36 10.4 0 197 358 595 728 912 1076 1282 1403 1596 1759		Figure 4.2.2. Plot of data to determine the DLOP/RQL for sec-Butyl Acetate on charcoal tubes. (y = 168x + 25.6)
Table 4.2.3 Detection Limit of the Overall Procedure for tert-Butyl Acetate Collected on Charcoal Tubes mass per sample (µg) area counts (µV•s) 0 1.03 2.06 3.09 4.12 5.15 6.18 7.21 8.24 9.27 10.3 0 193 397 489 696 792 894 1122 1252 1453 1629		Figure 4.2.3. Plot of data to determine the DLOP/RQL for tert-Butyl Acetate on charcoal tubes. (y = 152x + 28.2)
Table 4.2.4 Detection Limit of the Overall Procedure for Isobutyl Acetate Collected on Charcoal Tubes mass per sample (µg) area counts (µV•s) 0 1.04 2.08 3.12 4.16 5.20 6.24 7.28 8.32 9.36 10.4 0 219 406 634 734 969 1147 1372 1578 1719 1826		Figure 4.2.4. Plot of data to determine the DLOP/RQL for Isobutyl Acetate on charcoal tubes. (y = 180x + 30.6)
Table 4.2.5 Detection Limit of the Overall Procedure for n-Butyl Acetate Collected on 3M 3520 OVM mass per sample (µg) area counts (µV•s) 0 1.06 212 3.18 4.24 5.30 6.36 7.42 8.48 9.54 10.6 0 99 203 314 360 467 563 664 783 886 989		Figure 4.2.5. Plot of data to determine the DLOP/RQL for n-Butyl Acetate on 3M 3520 OVM. (y = 92.1x -3.64)
Table 4.2.6 Detection Limit of the Overall Procedure for sec-Butyl Acetate Collected on 3M 3520 OVMs mass per sample (µg) area counts (µV•s) 0 1.04 2.08 3.12 4.16 5.20 6.24 7.28 8.32 9.36 10.4 0 85 194 273 353 428 511 631 756 808 916		Figure 4.2.6. Plot of data to determine the DLOP/RQL for sec-Butyl Acetate collected on 3M 3520 OVM. (y = 87.7x - 5.55)
Table 4.2.7 Detection Limit of the Overall Procedure for tert-Butyl Acetate Collected on 3M 3520 OVMs mass per sample (µg) area counts (µV•s) 0 1.03 2.06 3.09 4.12 5.15 6.18 7.21 8.24 9.27 10.3 0 95 185 234 300 359 442 556 639 726 817		Figure 4.2.7. Plot of data to determine the DLOP/RQL for tert-Butyl Acetate collected on 3M 3520 OVM. (y = 77.3x – 2.32)
Table 4.2.8 Detection Limit of the Overall Procedure for Isobutyl Acetate Collected on 3M 3520 OVMs mass per sample (µg) area counts (µV•s) 0 1.04 2.08 3.12 4.16 5.20 6.24 7.28 8.32 9.36 10.4 0 113 209 308 366 498 571 667 760 838 960		Figure 4.2.8. Plot of data to determine the DLOP/RQL for Isobutyl Acetate collected on 3M 3520 OVM. (y = 89.8x + 13.8)
Table 4.2.9 Detection Limit of the Overall Procedure for n-Butyl Acetate Collected on SKC 575-002 Passive Samplers mass per sample (µg) area counts (µV•s) 0 1.06 2.12 3.18 4.24 5.30 6.36 7.42 8.48 9.54 10.6 0 103 201 279 398 474 590 712 783 901 1017		Figure 4.2.9. Plot of data to determine the DLOP/RQL for n-Butyl Acetate collected on SKC 575-002 Passive Samplers. (y = 95.0x – 7.50)
Table 4.2.10 Detection Limit of the Overall Procedure for sec-Butyl Acetate Collected on SKC 575-002 Passive Samplers mass per sample (µg) area counts (µV•s) 0 1.04 2.08 3.12 4.16 5.20 6.24 7.28 8.32 9.36 10.4 0 93 186 284 371 432 549 639 749 834 924		Figure 4.2.10. Plot of data to determine the DLOP/RQL for sec-Butyl Acetate collected on SKC 575-002 Passive Samplers. (y = 88.8x – 1.77)
Table 4.2.11 Detection Limit of the Overall Procedure for tert-Butyl Acetate Collected on SKC 575-002 Passive Samplers mass per sample (µg) area counts (µV•s) 0 1.03 2.06 3.09 4.12 5.15 6.18 7.21 8.24 9.27 10.3 0 81 156 236 308 353 452 536 639 718 819		Figure 4.2.11. Plot of data to determine the DLOP/RQL for tert-Butyl Acetate collected on SKC 575-002 Passive Samplers. (y = 78.0x – 10.9)
Table 4.2.12 Detection Limit of the Overall Procedure for Isobutyl Acetate Collected on SKC 575-002 Passive Samplers mass per sample (µg) area counts (µV•s) 0 1.04 2.08 3.12 4.16 5.20 6.24 7.28 8.32 9.36 10.4 0 112 214 303 390 471 570 639 754 876 997		Figure 4.2.12. Plot of data to determine the DLOP/RQL for Isobutyl Acetate collected on SKC 575-002 Passive Samplers. (y = 91.9x + 6.32)

The RQL is considered the lower limit for precise quantitative measurements. It is determined from the regression line parameters obtained for the calculation of the DLOP, providing 75% to 125% of the analyte is recovered. The RQLs for the various media are listed in Table 4.2.13.

Figure 4.2.13. A chromatogram of the RQL collected on charcoal tubes (lot 2000). (Key: (1) tert-Butyl Acetate, (2) interference, (3) sec-Butyl Acetate, (4) Isobutyl Acetate, and (5) n-Butyl Acetate.)

Figure 4.2.14. A chromatogram of the RQL collected on 3M 3520 OVM. (Key: (1) tert-Butyl Acetate, (2) interference, (3) sec-Butyl Acetate, (4) Isobutyl Acetate, and (5) n-Butyl Acetate.)

Figure 4.2.15. A chromatogram of the RQL collected on SKC 575-002 Passive Samplers. (Key: (1) tert-Butyl Acetate, (2) interference, (3) sec-Butyl Acetate, (4) Isobutyl Acetate, and (5) n-Butyl Acetate.)

4.3 Instrument calibration

The standard error of estimate was determined from the linear regression of data points from standards over a range that covers 0.25 to 2 times the TWA target concentration for charcoal tubes. This was the sampler with the highest mass loadings. Calibration curves were constructed and shown in Section 3.5.2 from the three injections each of five standards. The standard errors of estimate are 301 μg/sample for n-Butyl Acetate, 453 μg/sample for sec-Butyl Acetate, 386 μg/sample for tert-Butyl Acetate, and 398 μg/sample for Isobutyl Acetate.

Table 4.3.1 Instrument Calibration for n-Butyl Acetate
standard concn (μg/sample)	area counts (μV•s)
2130 4270 8540 12800 17100	311555 642069 1344755 2026181 2716357	311924 639046 1348169 2020191 2743667	314471 642301 1340858 2031066 2727599

Table 4.3.2 Instrument Calibration for sec-Butyl Acetate
standard concn (μg/sample)	area counts (μV•s)
2850 5710 11400 17100 22800	389300 826814 1713183 2600237 3514853	388180 823766 1734114 2601793 3498099	389547 834708 1725815 2616272 3521737

Table 4.3.3 Instrument Calibration for tert-Butyl Acetate
standard concn (μg/sample)	area counts (μV•s)
2850 5690 11400 17100 22800	396211 831572 1743547 2645741 3548909	401771 839092 1755744 2659639 3536631	400285 840213 1748131 2639678 3531375

Table 4.3.4 Instrument Calibration for Isobutyl Acetate
standard concn (μg/sample)	area counts (μV•s)
2130 4270 8540 12800 17100	304059 646407 1343710 2079543 2777187	308630 643795 1364685 2065334 2789088	306997 652459 1349883 2053967 2792043

4.4 Precision (overall procedure)

4.4.1 Charcoal tubes
 

The precision at the 95% confidence level is obtained by multiplying the standard error of estimate by 1.96 (the z-statistic from the standard normal distribution at the 95% confidence level) of ambient temperature 17-day storage samples. In Section 4.5, 95% confidence intervals are drawn about their respective regression lines in the storage graph figures. The precisions of the overall procedure are shown in Table 4.4.1 and were calculated from data in Section 4.5.

Table 4.4.1 Standard Error of Estimate and Precision of the Overall Procedure for Charcoal tubes analyte SEE (%) precision (± %) n-Butyl Acetate sec-Butyl Acetate tert-Butyl Acetate Isobutyl Acetate 5.03 5.02 5.03 5.06 9.86 9.84 9.86 9.92

4.4.2 3M 3520 OVMs

The precisions of the overall procedure at the 95% confidence level for the ambient temperature 17-day storage test (at the target concentration) for 3M 3520 OVMs are given in Table 4.4.2. They each include an additional 6.4% for sampling rate variability. There are different values given, depending on whether both, either, or neither temperature (T) or atmospheric pressure (P) are known at the sampling site. If the sampling site temperature is unknown, it is assumed to be 22.2 ± 15ºC (72 ± 27ºF) and a variability of ±7.7% is included. If the atmospheric pressure is not known, it is estimated from the sampling site elevation and a variability of ±3% is included.

Table 4.4.2 Precision of the Overall Procedure for 3M 3520 OVMs
	n-Butyl Acetate		sec-Butyl Acetate		tert-Butyl Acetate		Isobutyl Acetate
known conditions	SEE (%)	precision (± %)	SEE (%)	precision (± %)	SEE (%)	precision (± %)	SEE (%)	precision (± %)
both T & P only T only P neither T nor P	6.62 7.27 10.2 10.6	13.0 14.2 20.0 20.8	6.68 7.32 10.2 10.6	13.1 14.3 20.0 20.8	6.58 7.23 10.1 10.6	12.9 14.2 19.9 20.8	6.62 7.27 10.2 10.6	13.0 14.2 20.0 20.8

4.4.3 SKC 575-002 Passsive Samplers

The precisions of the overall procedure at the 95% confidence level for the ambient temperature 17-day storage test (at the target concentration) for SKC 575-002 Passive Samplers are given in Table 4.4.3. They each include an additional 8.7% for sampling rate variability. There are different values given, depending on whether both, either, or neither temperature (T) or atmospheric pressure (P) are known at the sampling site. If the sampling site temperature is unknown, it is assumed to be 22.2 ± 15ºC (72 ± 27ºF) and a variability of ±7.7% is included. If the atmospheric pressure is not known, it is estimated from the sampling site elevation and a variability of ±3% is included.

Table 4.4.3 Precision of the Overall Procedure for SKC 575-002 Passive Samplers
	n-Butyl Acetate		sec-Butyl Acetate		tert-Butyl Acetate		Isobutyl Acetate
known conditions	SEE (%)	precision (± %)	SEE (%)	precision (± %)	SEE (%)	precision (± %)	SEE (%)	precision (± %)
both T & P only T only P neither T nor P	8.88 9.37 11.8 12.1	17.4 18.4 23.1 23.7	8.88 9.37 11.8 12.1	17.4 18.4 23.1 23.7	8.92 9.41 11.8 12.2	17.5 18.4 23.1 23.9	8.89 9.38 11.8 12.1	17.4 18.4 23.1 23.7

4.5 Storage test

4.5.1 Charcoal tubes

Storage samples for n-Butyl Acetate, sec-Butyl Acetate, tert-Butyl Acetate, and Isobutyl Acetate were individually prepared by collecting samples from separate controlled test atmospheres using the recommended sampling conditions for charcoal tubes. The concentrations were at the target concentration. The atmospheres tested were: n-Butyl Acetate (718 mg/m³ or 151 ppm), sec-Butyl Acetate (955 mg/m³ or 201 ppm), tert-Butyl Acetate (965 mg/m³ or 203 ppm), and Isobutyl Acetate (708 mg/m³ or 149 ppm), with an average relative humidity of 80% at 23ºC. Thirty-three storage samples were prepared for each analyte. Three samples were analyzed on the day of generation. Fifteen of the tubes were stored at reduced temperature (4ºC) and the other fifteen were stored in a closed drawer at ambient temperature (about 23ºC). At 3 to 4-day intervals, three samples were selected from each of the two storage sets and analyzed. Sample results are not corrected for extraction efficiency. The recoveries on day 17 were n-Butyl Acetate 96.0% for ambient and 97.7% for refrigerated storage; sec-Butyl Acetate 98.3% for ambient and 98.6% for refrigerated storage; tert-Butyl Acetate 97.8% for ambient and 97.8% for refrigerated storage, and Isobutyl Acetate 96.7% for ambient and 98.5% for refrigerated storage.

Table 4.5.1.1 Storage Test for n-Butyl Acetate on Charcoal Tubes
time (days)	ambient storage recovery (%)			refrigerated storage recovery (%)
0 3 7 10 14 17	100.2 99.3 98.8 97.3 96.9 95.7	100.4 98.6 99.0 98.1 97.5 96.9	99.8 99.4 98.4 96.9 96.6 95.1	99.7 100.1 98.6 98.5 97.3	99.4 99.8 98.7 98.9 98.6	99.8 99.4 97.9 97.6 97.9

Table 4.5.1.2 Storage Test for sec-Butyl Acetate on Charcoal Tubes
time (days)	ambient storage recovery (%)			refrigerated storage recovery (%)
0 3 7 10 14 17	100.0 99.8 98.6 98.9 98.8 97.6	99.6 99.9 99.3 98.4 99.1 98.9	100.1 100.0 98.9 98.8 98.6 98.3	100.1 99.2 98.6 99.4 98.2	99.7 99.0 99.1 99.0 99.1	100.0 99.4 99.0 98.9 98.5

Table 4.5.1.3 Storage Test for tert-Butyl Acetate on Charcoal Tubes
time (days)	ambient storage recovery (%)			refrigerated storage recovery (%)
0 3 7 10 14 17	99.7 98.7 99.0 98.2 98.8 96.9	99.8 99.3 98.7 98.6 98.4 97.3	100.3 98.1 99.1 98.9 98.6 98.1	99.3 99.0 98.6 99.2 98.0	99.9 99.3 99.1 98.9 97.4	100.2 99.4 99.3 98.6 98.3

Table 4.5.1.4 Storage Test for Isobutyl Acetate on Charcoal Tubes
time (days)	ambient storage recovery (%)			refrigerated storage recovery (%)
0 3 7 10 14 17	99.9 98.6 97.4 97.5 98.4 96.1	99.7 99.3 97.3 98.1 97.9 97.8	100.3 99.4 98.4 98.0 97.6 95.3	99.4 99.6 99.2 98.9 97.9	99.6 99.2 98.7 98.8 98.4	100.1 99.5 98.5 99.3 98.9

Figure 4.5.1.1.1. Ambient storage test for n-Butyl Acetate collected on charcoal tubes.		Figure 4.5.1.1.2. Refrigerated storage test for n-Butyl Acetate collected on charcoal tubes.
Figure 4.5.1.2.1. Ambient storage test for sec-Butyl Acetate collected on charcoal tubes.		Figure 4.5.1.2.2. Refrigerated storage test for sec-Butyl Acetate collected on charcoal tubes.
Figure 4.5.1.3.1. Ambient storage test for tert-Butyl Acetate collected on charcoal tubes.		Figure 4.5.1.3.2. Refrigerated storage test for tert-Butyl Acetate collected on charcoal tubes.
Figure 4.5.1.4.1. Ambient storage test for Isobutyl Acetate collected on charcoal tubes.		Figure 4.5.1.4.2. Refrigerated storage test for Isobutyl Acetate collected on charcoal tubes.

4.5.2 3M 3520 OVMs

Storage samples for n-Butyl Acetate, sec-Butyl Acetate, tert-Butyl Acetate, and Isobutyl Acetate were individually prepared by collecting samples from separate controlled test atmospheres using the recommended sampling conditions for 3M 3520 OVMs. The concentrations were at the target concentration. The atmospheres tested were: n-Butyl Acetate (718 mg/m³ or 151 ppm), sec-Butyl Acetate (955 mg/m³ or 201 ppm), tert-Butyl Acetate (965 mg/m³ or 203 ppm), and Isobutyl Acetate (708 mg/m³ or 149 ppm), with an average relative humidity of 80% at 23ºC. Thirty-three storage samples were prepared for each analyte. Three samples were analyzed on the day of generation. Fifteen of the 3M 3520 OVMs were stored at reduced temperature (4ºC) and the other fifteen were stored in a closed drawer at ambient temperature (about 23ºC). At 3 to 4-day intervals, three samples were selected from each of the two storage sets and analyzed. Sample results are not corrected for extraction efficiency. The recoveries on day 17 were n-Butyl Acetate 96.3% for ambient and 97.5% for refrigerated storage; sec-Butyl Acetate 96.1% for ambient and 97.2% for refrigerated storage, tert-Butyl Acetate 95.9% for ambient and 97.0% for refrigerated storage, and Isobutyl Acetate 96.6% for ambient and 97.6% for refrigerated storage.

Table 4.5.2.1 Storage Test for n-Butyl Acetate on 3M 3520 OVMs
time (days)	ambient storage recovery (%)			refrigerated storage recovery (%)
0 3 7 10 14 17	99.2 96.7 96.8 97.9 99.5 98.1	100.6 99.2 99.0 95.4 96.8 95.7	97.5 100.6 98.9 99.5 94.1 94.7	96.8 96.9 98.6 96.1 95.1	100.3 98.8 100.4 98.6 96.5	99.5 99.8 96.6 99.9 99.4

Table 4.5.2.2 Storage Test for sec-Butyl Acetate on 3M 3520 OVMs
time (days)	ambient storage recovery (%)			refrigerated storage recovery (%)
0 3 7 10 14 17	100.4 97.2 95.3 99.1 98.7 93.4	95.6 99.3 96.2 96.5 94.0 96.8	97.0 96.1 98.8 94.4 96.5 98.0	98.1 95.9 97.8 99.5 94.9	99.5 98.4 95.5 95.1 97.3	96.0 99.1 99.9 97.4 98.8

Table 4.5.2.3 Storage Test for tert-Butyl Acetate on 3M 3520 OVMs
time (days)	ambient storage recovery (%)			refrigerated storage recovery (%)
0 3 7 10 14 17	99.9 98.7 99.2 96.9 98.1 95.4	98.4 98.8 96.4 99.1 94.7 94.1	96.4 96.2 96.6 95.4 95.9 98.0	96.5 97.8 96.9 94.4 95.4	98.7 96.4 99.5 99.1 98.8	99.3 99.9 94.0 96.9 96.8

Table 4.5.2.4 Storage Test for Isobutyl Acetate on 3M 3520 OVMs
time (days)	ambient storage recovery (%)			refrigerated storage recovery (%)
0 3 7 10 14 17	100.1 99.8 98.7 95.6 94.9 96.4	99.8 98.6 99.9 98.5 97.5 98.9	96.7 96.3 96.6 99.1 98.8 94.1	96.7 99.9 95.6 98.7 94.2	99.3 96.5 99.3 99.8 98.7	99.6 98.8 99.9 95.5 99.8

Figure 4.5.2.1.1. Ambient storage test for n-Butyl Acetate collected on 3M 3520 OVMs.		Figure 4.5.2.1.2. Refrigerated storage test for n-butyl acetate collected on 3M 3520 OVMs.
Figure 4.5.2.2.1. Ambient storage test for sec-Butyl Acetate collected on 3M 3520 OVMs.		Figure 4.5.2.2.2. Refrigerated storage test for sec-butyl acetate collected on 3M 3520 OVMs.
Figure 4.5.2.3.1. Ambient storage test for tert-Butyl Acetate collected on 3M 3520 OVMs.		Figure 4.5.2.3.2. Refrigerated storage test for tert-Butyl Acetate collected on 3M 3520 OVMs.
Figure 4.5.2.4.1. Ambient storage test for Isobutyl Acetate collected on 3M 3520 OVMs.		Figure 4.5.2.4.2. Refrigerated storage test for Isobutyl Acetate collected on 3M 3520 OVMs.

4.5.3 SKC 575-002 Passive Samplers

Storage samples for n-Butyl Acetate, sec-Butyl Acetate, tert-Butyl Acetate, and Isobutyl Acetate were individually prepared by collecting samples from separate controlled test atmospheres using the recommended sampling conditions for SKC 575-002 Passive Samplers. The concentrations were at the target concentration. The atmospheres tested were: n-Butyl Acetate (718 mg/m³ or 151 ppm), sec-Butyl Acetate (955 mg/m³ or 201 ppm), tert-Butyl Acetate (965 mg/m³ or 203 ppm), and Isobutyl Acetate (708 mg/m³ or 149 ppm), with an average relative humidity of 80% at 23ºC. Thirty-three storage samples were prepared for each analyte. Three samples were analyzed on the day of generation. Fifteen of the SKC 575-002 Passive Samplers were stored at reduced temperature (4ºC) and the other fifteen were stored in a closed drawer at ambient temperature (about 22ºC). At 3 to 4-day intervals, three samples were selected from each of the two storage sets and analyzed. Sample results are not corrected for extraction efficiency. The recoveries on day 17 were n-Butyl Acetate 96.6% for ambient and 97.3% for refrigerated storage, sec-Butyl Acetate 96.9% for ambient and 98.0% for refrigerated storage, tert-Butyl Acetate 96.4% for ambient and 97.6% for refrigerated storage, and Isobutyl Acetate 96.5% for ambient and 97.2% for refrigerated storage.

Table 4.5.3.1 Storage Test for n-Butyl Acetate on SKC 575-002 Passive Samplers
time (days)	ambient storage recovery (%)			refrigerated storage recovery (%)
0 3 7 10 14 17	100.3 100.2 95.5 94.6 94.8 96.8	99.7 99.8 99.3 97.1 98.0 95.4	96.1 97.4 98.4 99.1 97.3 99.2	99.8 98.5 98.6 94.7 95.2	96.2 100.1 94.1 98.0 98.6	99.9 95.3 99.7 99.2 99.0

Table 4.5.3.2 Storage Test for sec-Butyl Acetate on SKC 575-002 Passive Samplers
time (days)	ambient storage recovery (%)			refrigerated storage recovery (%)
0 3 7 10 14 17	100.2 99.3 98.6 99.1 94.9 95.2	99.4 95.7 99.4 98.4 99.1 96.6	95.8 99.5 95.3 95.8 96.9 98.8	100.1 99.6 95.7 98.6 96.4	100.0 96.7 98.5 95.4 99.3	95.8 99.3 99.8 98.5 98.8

Table 4.5.3.3 Storage Test for tert-Butyl Acetate on SKC 575-002 Passive Samplers
time (days)	ambient storage recovery (%)			refrigerated storage recovery (%)
0 3 7 10 14 17	100.1 99.6 99.8 94.9 94.8 98.1	100.5 99.3 95.7 98.5 98.6 93.4	96.7 95.8 99.1 98.8 99.3 95.8	100.1 99.9 95.9 99.7 99.1	100.3 99.6 99.9 98.9 98.0	96.4 95.3 98.7 94.5 94.6

Table 4.5.3.4 Storage Test for Isobutyl Acetate on SKC 575-002 Passive Samplers
time (days)	ambient storage recovery (%)			refrigerated storage recovery (%)
0 3 7 10 14 17	100.2 100.1 95.0 95.4 96.6 96.0	98.6 96.4 99.9 98.5 94.9 94.7	95.8 99.0 98.9 98.0 98.9 98.8	99.9 96.4 99.4 94.8 97.9	99.5 99.5 95.1 99.4 98.3	96.1 99.8 98.7 98.6 94.4

Figure 4.5.3.1.1. Ambient storage test for n-Butyl Acetate collected on SKC 575-002 Passive Samplers.		Figure 4.5.3.1.2. Refrigerated storage test for n-Butyl Acetate collected on SKC 575-002 Passive Samplers.
Figure 4.5.3.2.1. Ambient storage test for sec-Butyl Acetate collected on SKC 575-002 Passive Samplers.		Figure 4.5.3.2.2. Refrigerated storage test for sec-Butyl Acetate collected on SKC 575-002 Passive Samplers.
Figure 4.5.3.3.1. Ambient storage test for tert-Butyl Acetate collected on SKC 575-002 Passive Samplers.		Figure 4.5.3.3.2. Refrigerated storage test for tert-Butyl Acetate collected on SKC 575-002 Passive Samplers.
Figure 4.5.3.4.1. Ambient storage test for Isobutyl Acetate collected on SKC 575-002 Passive Samplers.		Figure 4.5.3.4.2. Refrigerated storage test for Isobutyl Acetate collected on SKC 575-002 Passive Samplers.

4.6 Reproducibility

Six samples were prepared for each of the three types of samplers by collecting them from controlled test atmospheres similar to those used in the collection of the storage samples. The samples were submitted to the OSHA Salt Lake Technical Center for analysis, along with a draft copy of this method. The samples were analyzed after being stored at 4 ºC for 5 days for samplers containing n-Butyl Acetate and Isobutyl Acetate, and 19 days for sec-Butyl Acetate and tert-Butyl Acetate. Sample results were corrected for extraction efficiency. No sample result for n-Butyl Acetate, sec-Butyl Acetate, tert-Butyl Acetate, or Isobutyl Acetate had a deviation greater than the precision of the overall procedure determined in Section 4.4.

4.7 Sampler capacity

4.7.1 Charcoal tubes

The sampling capacity of the front section of charcoal tubes was tested by sampling from a dynamically generated test atmosphere of each of the compounds generated individually. The atmospheres tested were: n-Butyl Acetate (1435 mg/m³ or 302 ppm), sec-Butyl Acetate (1910 mg/m³ or 402 ppm), tert-Butyl Acetate (1930 mg/m³ or 406 ppm) and Isobutyl Acetate (1416 mg/m³ or 298 ppm) with an average relative humidity of 80% at 23ºC. This air concentration was twice the PEL. A sampling train consisting of the front section of a charcoal tube (back-up section removed) in series with another charcoal tube was used to test the capacity. The second tube was changed at 0.5 h intervals and was analyzed. The second tube was replaced with a fresh tube and then sampling was continued. Two separate charcoal tube sampling trains were collected for each analyte from the given test atmosphere. These sampling trains were used to sample for 3, 4, 5, 6, 6.5, 7, 7.5, and 8 hours for n-Butyl Acetate and Isobutyl Acetate, and 2, 3, 4, 4.5, 5, 5.5, and 6 hours for sec-Butyl Acetate and tert-Butyl Acetate. The charcoal tube sampling trains were collected at approximately 0.05 L/min (the air volumes listed below are cumulative for each sampling train and were calculated using that specific sampling train’s flow rate). The presence of analyte on the second tube is an indication breakthrough. The percentage of the amount found on the second tube of the total concentration is the % breakthrough. The % breakthrough was plotted versus the time sampled to determine the 5% breakthrough air volumes. The 5% breakthrough air volume was determined to be 25.0 L for n-Butyl Acetate, 17.1 L for sec-Butyl Acetate, and 18.1 L for tert-Butyl Acetate, and 25.2 L for Isobutyl Acetate.

Table 4.7.1.1 Capacity Test for n-Butyl Acetate on Charcoal Tubes
sampling train 1		sampling train 2
air volume	% BT	air volume	% BT
9.22 12.3 15.4 18.4 20.0 21.5 23.0 24.6	0.0 0.0 0.0 0.0 0.0 0.3 1.9 5.9	9.65 12.9 16.1 19.3 20.9 22.5 24.1 25.7	0.0 0.0 0.0 0.0 0.0 0.5 2.5 7.1
%BT = % breakthrough

Table 4.7.1.2 Capacity Test for sec-Butyl Acetate on Charcoal Tubes
sampling train 1		sampling train 2
air volume	% BT	air volume	% BT
6.46 9.68 12.9 14.5 16.1 17.7 19.4	0.0 0.0 0.4 1.0 3.5 8.3 15.4	6.89 10.3 13.8 15.5 17.2 18.9 20.7	0.0 0.0 0.6 1.2 4.3 9.9 17.4
%BT = % breakthrough

Table 4.7.1.3 Capacity Test for tert-Butyl Acetate on Charcoal Tubes
sampling train 1		sampling train 2
air volume	% BT	air volume	% BT
6.32 9.49 12.7 14.2 15.8 17.4 19.0	0.0 0.0 0.0 0.0 1.5 3.9 9.8	6.35 9.52 12.7 14.3 15.9 17.5 19.0	0.0 0.0 0.0 0.0 0.8 2.8 10.3
%BT = % breakthrough

Table 4.7.1.4 Capacity Test for Isobutyl Acetate on Charcoal Tubes
sampling train 1		sampling train 2
air volume	% BT	air volume	% BT
9.59 12.8 16.0 19.2 20.8 22.4 24.0 25.6	0.0 0.0 0.0 0.0 0.1 0.5 2.1 8.6	10.2 13.6 17.0 20.4 22.1 23.8 25.5 27.2	0.0 0.0 0.0 0.0 0.4 1.1 3.9 10.5
%BT = % breakthrough

Figure 4.7.1.1. Five percent breakthough air volume for n-Butyl Acetate on charcoal tubes, calculated to be 25.0 L.		Figure 4.7.1.2. Five percent breakthough air volume for sec-Butyl Acetate on charcoal tubes, calculated to be 17.1 L.
Figure 4.7.1.3. Five percent breakthrough air volume for tert-Butyl Acetate on charcoal tubes, calculated to be 18.1 L.		Figure 4.7.1.4. Five percent breakthough air volume for Isobutyl Acetate on charcoal tubes, calculated to be 25.2 L.

4.7.2 3M 3520 OVMs

The sampling rate and sampler capacity are determined with samples collected for increasing time intervals from a controlled test atmosphere. Each analyte was tested separately. The concentration of the test atmosphere was two times the target concentration with an average relative humidity of approximately 80% at 23°C. The atmospheres tested were: n-Butyl Acetate (1449 mg/m³ or 305 ppm), sec-Butyl Acetate (1892 mg/m³ or 398 ppm), tert-Butyl Acetate (1925 mg/m³ or 405 ppm) and Isobutyl Acetate (1430 mg/m³ or 301 ppm). Three samplers were exposed for each test. Sampling rates were determined at ambient temperature and pressure, but were converted to their equivalent at 760 mm and 25 °C. The preliminary sampling rate was determined by averaging the nine values for the 0.5, 1 and 2 h samples. Horizontal lines were placed 10% above and below the preliminary sampling rate. The average sampling rates of all values between the lines were 31.19 mL/min n-Butyl Acetate, 28.11 mL/min sec-Butyl Acetate, 28.94 mL/min tert-Butyl Acetate, and 30.43 mL/min Isobutyl Acetate. The standard deviation and RSD are 1.01 mL/min and 3.24% for n-Butyl Acetate, 1.14 mL/min and 4.07% for sec-Butyl Acetate, 0.956 mL/min and 3.30% for tert-Butyl Acetate, and 1.25 mL/min and 4.11% for Isobutyl Acetate, respectively. Mass collected is corrected for extraction efficiency. The sampler capacity is exceeded when the sampling rate decreases (greater than 4.8 hours for tert-Butyl Acetate, and greater than 6.4 hours for n-Butyl Acetate, sec-Butyl Acetate, and Isobutyl Acetate). The recommended sampling time is 4h for TWA samples and 15 min for short term samples.

Table 4.7.2.1 Determination of Sampling Rate and Time of n-Butyl Acetate for 3M 3520 OVMs from a 305-ppm Atmosphere time (h) sampling rate (mL/min) first second third 0.083 0.167 0.25 0.5 1 2 3 4 6 8 10 29.29 29.43 31.26 30.65 31.38 31.05 31.94 32.98 31.99 31.12 28.19 28.47 31.10 31.16 31.41 32.52 31.45 30.97 31.64 31.08 29.56 29.89 30.01 30.47 30.61 32.59 30.96 32.78 32.88 32.75 30.55 30.24 27.58		Figure 4.7.2.1. The 3M 3520 OVM data in Table 4.7.2.1 plotted to determine the recommended sampling time and sampling rate of n-Butyl Acetate from a 305-ppm atmosphere.
Table 4.7.2.2 Determination of Sampling Rate and Time of sec-Butyl Acetate for 3M 3520 OVMs from a 398-ppm Atmosphere time (h) sampling rate (mL/min) first second third 0.083 0.167 0.25 0.5 1 2 3 4 6 8 10 26.45 27.29 27.46 28.26 28.33 28.52 29.54 28.68 27.82 26.99 22.23 25.88 26.99 27.45 28.34 28.12 28.46 28.71 29.88 28.79 26.11 23.54 25.12 27.71 28.61 29.55 29.49 29.19 29.79 29.29 27.01 26.34 23.11		Figure 4.7.2.2. The 3M 3520 OVM data in Table 4.7.2.2 plotted to determine the recommended sampling time and sampling rate of sec-Butyl Acetate from a 398-ppm atmosphere.
Table 4.7.2.3 Determination of Sampling Rate and Time of tert-Butyl Acetate for 3M 3520 OVMs from a 405-ppm Atmosphere time (h) sampling rate (mL/min) first second third 0.083 0.167 0.25 0.5 1 2 3 4 6 8 10 27.67 28.97 28.45 29.17 29.37 29.89 30.43 29.42 27.99 26.88 23.38 27.23 28.56 28.99 29.02 29.44 30.21 30.08 30.02 28.51 27.01 23.99 27.54 28.79 29.11 28.73 29.88 29.65 29.88 29.73 29.03 26.44 23.45		Figure 4.7.2.3. The 3M 3520 OVM data in Table 4.7.2.3 plotted to determine the recommended sampling time and sampling rate of tert-Butyl Acetate from a 405-ppm atmosphere.
Table 4.7.2.4 Determination of Sampling Rate and Time of Isobutyl Acetate for 3M 3520 OVMs from a 301-ppm Atmosphere time (h) sampling rate (mL/min) first second third 0.083 0.167 0.25 0.5 1 2 3 4 6 8 10 27.46 28.30 30.25 30.49 30.31 31.40 31.19 30.45 31.66 29.43 28.25 28.23 28.98 29.24 29.95 30.67 32.01 32.11 31.53 29.67 28.55 29.33 27.92 29.48 29.89 31.36 32.09 32.43 32.58 32.12 30.33 30.71 27.66		Figure 4.7.2.4. The 3M 3520 OVM data in Table 4.7.2.4 plotted to determine the recommended sampling time and sampling rate of Isobutyl Acetate from a 301-ppm atmosphere.

4.7.3 SKC 575-002 Passive Samplers

The sampling rate and sampler capacity are determined with samples collected for increasing time intervals from a controlled test atmosphere. Each analyte was tested separately. The concentration of the test atmosphere was two times the target concentration with an average relative humidity of approximately 80% at 23°C. The atmospheres tested were: n-Butyl Acetate (1449 mg/m³ or 305 ppm), sec-Butyl Acetate (1892 mg/m³ or 398 ppm), tert-Butyl Acetate (1925 mg/m³ or 405 ppm), and Isobutyl Acetate (1430 mg/m³ or 301 ppm) with a relative humidity of 80% at 23°C. Sampling rates were determined at ambient temperature and pressure, but were converted to their equivalent at 760 mm and 25 °C. Three samplers were exposed for each test. The preliminary sampling rate was determined by averaging the nine values for the 0.5, 1 and 2 h samples. Horizontal lines were placed 10% above and below the preliminary sampling rate. The average sampling rates of all values between the lines were 13.07 mL/min n-Butyl Acetate, 12.74 mL/min sec-Butyl Acetate, 13.09 mL/min tert-Butyl Acetate, and 13.16 mL/min Isobutyl Acetate. The standard deviation and RSD are 0.460 mL/min and 3.61% for n-Butyl Acetate, 0.570 mL/min and 4.38% for sec-Butyl Acetate, 0.473 mL/min and 3.61% for tert-Butyl Acetate, and 0.536 mL/min and 4.07% for Isobutyl Acetate respectively. Mass collected is corrected for extraction efficiency. The sampler capacity is exceeded when the sampling rate decreases (greater than 4.8 hours for tert-Butyl Acetate, and greater than 6.4 hours for n-Butyl Acetate, sec-Butyl Acetate, and Isobutyl Acetate). The recommended sampling time is 4 h for TWA samples and 15 min for short term samples.

Table 4.7.3.1 Determination of Sampling Rate and Time of n-Butyl Acetate for SKC 575-002 Passive Samplers from a 305-ppm Atmosphere time (h) sampling rate (mL/min) first second third 0.083 0.167 0.25 0.5 1 2 3 4 6 8 10 12.02 12.41 13.03 13.17 13.19 13.48 13.59 13.43 13.27 12.40 11.90 11.79 12.32 12.78 13.07 13.41 13.52 13.66 13.65 13.03 12.53 12.16 12.18 12.15 13.12 13.29 13.34 13.27 13.45 13.76 13.32 12.75 11.59		Figure 4.7.3.1. The SKC 575-002 Passive Sampler data in Table 4.7.3.1 plotted to determine the recommended sampling time and sampling rate of n-Butyl Acetate from a 305-ppm atmosphere.
Table 4.7.3.2 Determination of Sampling Rate and Time of sec-Butyl Acetate for SKC 575-002 Passive Samplers from a 398-ppm Atmosphere time (h) sampling rate (mL/min) first second third 0.083 0.167 0.25 0.5 1 2 3 4 6 8 10 11.99 12.54 12.70 12.96 13.17 13.66 13.56 13.57 12.56 12.11 11.26 11.86 12.30 12.65 13.28 13.68 13.41 13.81 13.82 12.71 12.39 11.09 12.21 12.47 13.01 12.88 13.55 13.29 13.91 13.39 12.99 12.47 11.42		Figure 4.7.3.2. The SKC 575-002 Passive Sampler data in Table 4.7.3.2 plotted to determine the recommended sampling time and sampling rate of sec-Butyl Acetate from a 398-ppm atmosphere.
Table 4.7.3.3 Determination of Sampling Rate and Time of tert-Butyl Acetate for SKC 575-002 Passive Samplers from a 405-ppm Atmosphere time (h) sampling rate (mL/min) first second third 0.083 0.167 0.25 0.5 1 2 3 4 6 8 10 12.73 12.65 13.19 13.13 13.61 13.71 13.50 13.39 12.72 12.07 11.57 12.57 12.91 13.09 13.31 13.25 13.84 13.73 13.21 12.58 12.43 11.34 12.83 12.99 12.88 12.95 13.31 13.39 13.97 13.62 12.94 12.29 11.20		Figure 4.7.3.3. The SKC 575-002 Passive Sampler data in Table 4.7.3.3 plotted to determine the recommended sampling time and sampling rate of tert-Butyl Acetate from a 405-ppm atmosphere.
Table 4.7.3.4 Determination of Sampling Rate and Time of Isobutyl Acetate for SKC 575-002 Passive Samplers from a 301-ppm Atmosphere time (h) sampling rate (mL/min) first second third 0.083 0.167 0.25 0.5 1 2 3 4 6 8 10 12.11 12.40 12.75 12.96 12.99 14.02 14.10 13.89 13.50 12.98 11.74 11.65 12.59 12.81 13.09 13.10 13.55 13.76 13.42 13.10 12.71 12.24 12.29 12.88 13.21 13.33 13.42 13.68 13.87 13.65 13.41 13.11 11.87		Figure 4.7.3.4. The SKC 575-002 Passive Sampler data in Table 4.7.3.4 plotted to determine the recommended sampling time and sampling rate of Isobutyl Acetate from a 301-ppm atmosphere.

4.8 Extraction efficiency and stability of extracted samples

The extraction efficiency is dependent on the extraction solvent as well as the internal standard. The extraction solvent used for this evaluation consisted of carbon disulfide with 0.25 μL/mL n-hexyl benzene internal standard. Other extraction solvents or internal standards may be used provided that the new extraction solution or internal standard is tested. The new extraction solvent or internal standard should be tested as described below.

4.8.1 Charcoal tubes

Extraction efficiency

The extraction efficiencies of n-Butyl Acetate, sec-Butyl Acetate, tert-Butyl Acetate, and Isobutyl Acetate were separately determined by liquid-spiking the front section of four charcoal tubes, at each concentration level, with the analyte from the RQL to 2 times the target concentration. These samples were stored overnight at ambient temperature and then analyzed. The mean extraction efficiency over the working range from the RQL to 2 times the target concentration is 99.3% for n-Butyl Acetate, 99.2% for sec-Butyl Acetate, 99.3% for tert-Butyl Acetate, and 99.1% for Isobutyl Acetate. The extraction efficiency for the wet samplers was not included in the overall mean because it would bias the results. The test of wet samplers was performed to determine if the amount of water that would be collected under high humidity conditions at the recommended air volume would affect the extraction efficiency. Wet samplers were prepared by sampling humid air having an average relative humidity of about 80% at 23ºC for 240 minutes at 0.05 L/min and then liquid-spiking the sampler with the analyte.

Table 4.8.1.1 Extraction Efficiency (%) of n-Butyl Acetate from Charcoal Tubes
level		sample number				mean
× target concn	mg per sample	1	2	3	4
RQL 0.25 0.5 1.0 1.5 2.0 1.0 (wet)	0.002 2.14 4.28 8.56 12.8 17.1 8.56	98.3 98.8 99.7 98.7 99.0 99.6 98.1	98.2 99.7 98.8 99.5 99.3 99.9 99.7	99.9 99.1 99.9 99.8 98.9 98.8 98.6	99.4 99.9 99.6 99.5 99.7 99.8 99.4	99.0 99.4 99.5 99.4 99.2 99.5 99.0

Table 4.8.1.2 Extraction Efficiency (%) of sec-Butyl Acetate from Charcoal Tubes
level		sample number				mean
× target concn	mg per sample	1	2	3	4
RQL 0.25 0.5 1.0 1.5 2.0 1.0 (wet)	0.001 2.87 5.74 11.5 17.2 23.0 11.5	98.8 99.9 99.7 98.7 99.6 99.9 98.6	99.5 97.9 98.6 99.5 98.5 99.1 99.0	98.3 98.8 99.8 99.4 99.1 98.5 98.1	97.3 99.6 99.4 99.9 99.8 99.8 97.7	98.5 99.1 99.4 99.4 99.3 99.4 98.4

Table 4.8.1.3 Extraction Efficiency (%) of tert-Butyl Acetate from Charcoal Tubes
level		sample number				mean
× target concn	mg per sample	1	2	3	4
RQL 0.25 0.5 1.0 1.5 2.0 1.0 (wet)	0.003 2.84 5.67 11.3 17.0 22.7 11.3	98.6 98.8 97.9 99.1 99.9 99.4 97.6	99.5 99.7 99.5 99.3 99.6 99.9 99.0	97.4 98.9 99.7 99.9 99.2 99.7 98.3	98.9 99.4 99.8 99.7 99.6 98.9 98.9	98.6 99.2 99.2 99.5 99.6 99.5 98.5

Table 4.8.1.4 Extraction Efficiency (%) of Isobutyl Acetate from Charcoal Tubes
level		sample number				mean
× target concn	mg per sample	1	2	3	4
RQL 0.25 0.5 1.0 1.5 2.0 1.0 (wet)	0.002 2.15 4.29 8.58 12.9 17.2 8.58	98.3 98.5 99.4 99.8 98.8 99.6 97.4	99.6 99.8 98.9 99.1 99.8 98.1 99.5	99.0 98.7 99.5 99.2 99.4 99.2 98.6	98.5 98.3 99.3 98.0 99.7 99.8 99.0	98.9 98.8 99.3 99.0 99.4 99.2 98.6

Stability of extracted samples

The stability of extracted samples was investigated by reanalyzing the target concentration samples 24 h after initial analysis. After the original analysis was performed two autosampler vials were recapped with new septa while the remaining two retained their punctured septa. The samples were reanalyzed with fresh standards. The average percent change was 0.0% for n-Butyl Acetate, -0.9% for sec-Butyl Acetate, 0.8% for tert-Butyl Acetate, and -0.7% for Isobutyl Acetate when samples were resealed with new septa and -1.8% for n-Butyl Acetate, -2.6% for sec-Butyl Acetate, -2.7% for tert-Butyl Acetate, and -2.0% for Isobutyl Acetate when samples retained their punctured septa. Each septum was punctured 5 times for each analysis. The test was performed at room temperature.

Table 4.8.1.5 Stability of Extracted Samples for n-Butyl Acetate on Charcoal Tubes
punctured septa replaced			punctured septa retained
initial (%)	after one day (%)	difference (%)	initial (%)	after one day (%)	difference (%)
98.7 99.5 99.1	99.2 99.0 (mean) 99.1	+0.5 -0.5 +0.0	99.8 99.5 99.6	97.6 98.1 (mean) 97.8	-2.2 -1.4 -1.8

Table 4.8.1.6 Stability of Extracted Samples for sec-Butyl Acetate on Charcoal Tubes
punctured septa replaced			punctured septa retained
initial (%)	after one day (%)	difference (%)	initial (%)	after one day (%)	difference (%)
98.7 99.5 99.1	97.9 98.5 (mean) 98.2	-0.8 -1.0 -0.9	99.4 99.9 96.6	97.2 96.9 (mean) 97.0	-2.2 -3.0 -2.6

Table 4.8.1.7 Stability of Extracted Samples for tert-Butyl Acetate on Charcoal Tubes
punctured septa replaced			punctured septa retained
initial (%)	after one day (%)	difference (%)	initial (%)	after one day (%)	difference (%)
99.1 99.3 99.2	98.6 98.2 (mean) 98.4	-0.5 -1.1 -0.8	99.9 99.7 99.8	97.5 96.7 (mean) 97.1	-2.4 -3.0 -2.7

Table 4.8.1.8 Stability of Extracted Samples for Isobutyl Acetate on Charcoal Tubes
punctured septa replaced			punctured septa retained
initial (%)	after one day (%)	difference (%)	initial (%)	after one day (%)	difference (%)
99.8 99.1 99.4	99.0 98.5 (mean) 98.7	-0.8 -0.6 -0.7	99.2 98.0 98.6	96.4 96.8 (mean) 97.6	-2.8 -1.2 -2.0

4.8.2 3M 3520 OVMs

Extraction efficiency

The extraction efficiencies of n-Butyl Acetate, sec-Butyl Acetate, tert-Butyl Acetate, and Isobutyl Acetate were separately determined by liquid-spiking four charcoal pads from 3M 3520 OVMs, at each concentration level, with the analyte from the RQL to 2 times the target concentration. These samples were stored overnight at ambient temperature and then analyzed. The mean extraction efficiency over the working range from the RQL to 2 times the target concentration is 98.9% for n-Butyl Acetate, 99.1% for sec-Butyl Acetate, 99.0% for tert-Butyl Acetate, and 99.2% for Isobutyl Acetate. The extraction efficiency for the wet samplers was not included in the overall mean because it would bias the results. The test of wet samplers was performed to determine if the amount of water that would be collected under high humidity conditions at the recommended air volume would affect the extraction efficiency. Wet samplers were prepared by sampling humid air having an average relative humidity of about 80% at 23ºC for 240 minutes and then liquid- spiking the sampler with the analyte.

Table 4.8.2.1 Extraction Efficiency (%) of n-Butyl Acetate from 3M 3520 OVMs
level		sample number				mean
× target concn	mg per sample	1	2	3	4
RQL 0.25 0.5 1.0 1.5 2.0 1.0 (wet)	0.002 1.34 2.69 5.37 8.06 10.8 5.28	98.5 99.0 98.4 99.4 99.7 99.5 99.3	97.5 98.8 98.7 98.5 99.6 99.0 99.1	97.7 99.4 99.2 97.9 99.5 99.3 98.4	98.1 98.9 99.0 99.5 98.7 98.5 98.8	98.0 99.0 98.8 98.8 99.4 99.1 98.9

Table 4.8.2.2 Extraction Efficiency (%) of sec-Butyl Acetate from 3M 3520 OVMs
level		sample number				mean
× target concn	mg per sample	1	2	3	4
RQL 0.25 0.5 1.0 1.5 2.0 1.0 (wet)	0.002 1.79 3.59 6.49 10.8 14.4 6.49	97.2 98.8 98.9 98.3 97.3 99.3 98.4	99.0 98.2 99.5 99.1 99.6 99.8 97.4	98.7 99.6 98.5 99.9 99.8 98.2 99.1	99.4 99.7 99.9 99.3 98.7 99.9 98.7	98.6 99.1 99.2 99.2 98.9 99.3 98.4

Table 4.8.2.3 Extraction Efficiency (%) of tert-Butyl Acetate from 3M 3520 OVMs
level		sample number				mean
× target concn	mg per sample	1	2	3	4
RQL 0.25 0.5 1.0 1.5 2.0 1.0 (wet)	0.003 1.80 3.61 7.22 10.8 14.4 7.22	98.5 99.6 98.1 99.4 99.0 99.7 98.6	99.3 99.1 98.7 99.0 99.2 99.0 96.9	98.6 98.7 99.8 99.9 99.9 99.8 98.1	97.7 98.1 99.0 98.6 98.5 98.9 98.5	98.5 98.9 98.9 99.2 99.2 99.4 98.0

Table 4.8.2.4 Extraction Efficiency (%) of Isobutyl Acetate from 3M 3520 OVMs
level		sample number				mean
× target concn	mg per sample	1	2	3	4
RQL 0.25 0.5 1.0 1.5 2.0 1.0 (wet)	0.002 1.39 2.69 5.38 8.06 10.8 5.38	99.1 98.9 99.4 98.7 99.6 99.9 99.3	98.5 99.9 99.7 99.5 98.1 98.9 98.8	98.7 98.6 98.7 99.7 99.7 99.6 99.5	99.0 99.5 99.8 99.0 98.9 99.3 98.9	98.8 99.2 99.4 99.2 99.1 99.4 99.1

There were two different procedures for extraction of 3M 3520 OVMs in Section 3.4.3. The first procedure was extraction inside the 3M 3520 OVM by adding 2 mL of extraction solvent, inserting the caps, and extracting for 30 min. In the second procedure the charcoal pads were removed from the sampler, placed into separate 4-mL vials, 2 mL of extraction solvent added, the vials capped, and extracted for 30 min. A comparison of the two extraction procedures of 3M 3520 OVMs using n-Butyl Acetate at one times the target concentration showed little difference in the recoveries.

Table 4.8.2.5 Comparison of Recoveries (%) Using Two Extraction Procedures of n-Butyl Acetate from 3M 3520 OVMs
extraction procedure	sample number				mean
	1	2	3	4
inside 3M OVM sampler charcoal pad inside vial	99.4 99.9	98.5 99.1	97.9 98.2	99.5 98.3	98.8 98.9

Stability of extracted samples

The stability of extracted samples was investigated by reanalyzing the target concentration samples 24 h after initial analysis. After the original analysis was performed two autosampler vials were recapped with new septa while the remaining two retained their punctured septa. The samples were reanalyzed with fresh standards. The average percent change was -0.4% for n-Butyl Acetate, 1.0% for sec-Butyl Acetate, -1.0% for tert-Butyl Acetate, and -1.1% for Isobutyl Acetate when samples were resealed with new septa and -1.0% for n-Butyl Acetate, 2.5% for sec-Butyl Acetate, -3.0% tert-Butyl Acetate, and -2.2% for Isobutyl Acetate when samples retained their punctured septa. Each septum was punctured 5 times for each analysis. The test was performed at room temperature.

Table 4.8.2.6 Stability of Extracted Samples for n-Butyl Acetate on 3M 3520 OVMs
punctured septa replaced			punctured septa retained
initial (%)	after one day (%)	difference (%)	initial (%)	after one day (%)	difference (%)
99.4 98.5 99.0	99.0 98.2 (mean) 98.6	-0.4 -0.3 -0.4	97.9 99.5 98.7	97.5 97.9 (mean) 97.7	-0.4 -1.6 -1.0

Table 4.8.2.7 Stability of Extracted Samples for sec-Butyl Acetate on 3M 3520 OVMs
punctured septa replaced			punctured septa retained
initial (%)	after one day (%)	difference (%)	initial (%)	after one day (%)	difference (%)
98.3 99.1 98.7	97.1 98.3 (mean) 97.7	-1.2 -0.8 -1.0	99.9 99.3 99.6	96.5 97.7 (mean) 97.1	-3.4 -1.6 -2.5

Table 4.8.2.8 Stability of Extracted Samples for tert-Butyl Acetate on 3M 3520 OVMs
punctured septa replaced			punctured septa retained
initial (%)	after one day (%)	difference (%)	initial (%)	after one day (%)	difference (%)
99.4 99.0 99.2	97.6 98.8 (mean) 98.2	-1.8 -0.2 -1.0	99.9 98.6 99.2	96.7 95.8 (mean) 96.2	-3.2 -2.8 -3.0

Table 4.8.2.9 Stability of Extracted Samples for Isobutyl Acetate on 3M 3520 OVMs
punctured septa replaced			punctured septa retained
initial (%)	after one day (%)	difference (%)	initial (%)	after one day (%)	difference (%)
98.7 99.5 99.1	97.5 98.5 (mean) 98.0	-1.2 -1.0 -1.1	99.7 99.0 99.4	97.9 96.4 (mean) 97.2	-1.8 -2.6 -2.2

4.8.3 SKC 575-002 Passive Samplers

Extraction efficiency

The extraction efficiencies of n-Butyl Acetate, sec-Butyl Acetate, tert-Butyl Acetate, and Isobutyl Acetate were separately determined by liquid-spiking four SKC 575-002 Passive Samplers, at each concentration level, with the analyte from the RQL to 2 times the target concentration. These samples were stored overnight at ambient temperature and then analyzed. The mean extraction efficiency over the working range from the RQL to 2 times the target concentration is 99.2% for n-Butyl Acetate, 99.1% for sec-Butyl Acetate, 98.9% for tert-Butyl Acetate, and 99.1% for Isobutyl Acetate. The extraction efficiency for the wet samplers was not included in the overall mean because it would bias the results. The test of wet samplers was performed to determine if the amount of water that would be collected under high humidity conditions at the recommended air volume, would affect the extraction efficiency. Wet samplers were prepared by sampling humid air having an average relative humidity of about 80% at 23ºC for 240 minutes and then liquid-spiking the sampler with the analyte.

Table 4.8.3.1 Extraction Efficiency (%) of n-Butyl Acetate from SKC 575-002 Passive Samplers
level		sample number				mean
× target concn	mg per sample	1	2	3	4
RQL 0.25 0.5 1.0 1.5 2.0 1.0 (wet)	0.002 0.55 1.10 2.21 3.31 4.41 2.21	98.0 99.9 99.4 99.0 99.6 99.5 98.2	99.4 98.2 99.1 99.3 98.9 99.2 99.2	98.4 99.1 99.9 98.5 99.7 98.8 97.6	99.9 98.8 99.8 99.5 99.1 99.7 98.4	98.9 99.0 99.6 99.1 99.3 99.3 98.3

Table 4.8.3.2 Extraction Efficiency (%) of sec-Butyl Acetate from SKC 575-002 Passive Samplers
level		sample number				mean
× target concn	mg per sample	1	2	3	4
RQL 0.25 0.5 1.0 1.5 2.0 1.0 (wet)	0.001 0.74 1.47 2.94 4.41 5.88 2.94	97.8 99.7 98.5 99.4 99.7 99.9 98.1	99.6 99.9 99.3 99.0 99.9 99.3 97.5	98.4 97.4 99.0 98.9 98.8 98.5 98.6	98.1 98.7 99.9 99.9 99.6 99.5 99.0	98.5 98.9 99.2 99.3 99.5 99.3 98.3

Table 4.8.3.3 Extraction Efficiency (%) of tert-Butyl Acetate from SKC 575-002 Passive Samplers
level		sample number				mean
× target concn	mg per sample	1	2	3	4
RQL 0.25 0.5 1.0 1.5 2.0 1.0 (wet)	0.002 0.734 1.47 2.94 4.41 5.88 2.94	97.8 98.1 98.3 99.5 99.3 98.9 97.7	99.0 99.4 99.9 99.1 99.5 99.9 98.1	98.0 98.1 99.3 98.5 99.0 99.5 96.8	98.5 98.6 98.9 99.7 98.1 99.0 99.1	98.3 98.6 99.1 99.2 99.0 99.3 97.9

Table 4.8.3.4 Extraction Efficiency (%) of Isobutyl Acetate from SKC 575-002 Passive Samplers
level		sample number				mean
× target concn	mg per sample	1	2	3	4
RQL 0.25 0.5 1.0 1.5 2.0 1.0 (wet)	0.002 0.55 1.11 2.21 3.32 4.42 2.21	98.6 98.4 97.9 99.3 99.5 99.2 99.1	99.6 99.3 99.5 99.9 99.7 99.9 98.9	97.8 97.9 99.9 99.7 98.9 98.8 97.8	98.5 99.5 98.9 98.6 99.1 99.6 99.0	98.6 98.8 99.1 99.4 99.3 99.4 98.7

Stability of extracted samples

The stability of extracted samples was investigated by reanalyzing the target concentration samples 24 h after initial analysis. After the original analysis was performed two autosampler vials were recapped with new septa while the remaining two retained their punctured septa. The samples were reanalyzed with fresh standards. The average percent change was -0.5% for n-Butyl Acetate, 1.2% for sec-Butyl Acetate, 1.3% for tert-Butyl Acetate, and -1.3% for Isobutyl Acetate when samples were resealed with new septa and -2.3% for n-Butyl Acetate, 2.1% for sec-Butyl Acetate, -3.4% for tert-Butyl Acetate, and -2.9% for Isobutyl Acetate when samples retained their punctured septa. Each septum was punctured 5 times for each analysis. The test was performed at room temperature.

Table 4.8.3.5 Stability of Extracted Samples for n-Butyl Acetate on SKC 575-002 Passive Samplers
punctured septa replaced			punctured septa retained
initial (%)	after one day (%)	difference (%)	initial (%)	after one day (%)	difference (%)
99.0 99.3 99.2	98.8 98.6 (mean) 98.7	-0.2 -0.7 -0.5	98.5 99.5 99.0	96.1 97.3 (mean) 96.7	-2.4 -2.2 -2.3

Table 4.8.3.6 Stability of Extracted Samples for Isobutyl Acetate on SKC 575-002 Passive Samplers
punctured septa replaced			punctured septa retained
initial (%)	after one day (%)	difference (%)	initial (%)	after one day (%)	difference (%)
99.3 99.9 99.6	98.1 98.5 (mean) 98.3	-1.2 -1.4 -1.3	99.7 98.6 99.2	96.1 96.5 (mean) 96.3	-3.6 -2.1 -2.9

Table 4.8.3.7 Stability of Extracted Samples for sec-Butyl Acetate on SKC 575-002 Passive Samplers
punctured septa replaced			punctured septa retained
initial (%)	after one day (%)	difference (%)	initial (%)	after one day (%)	difference (%)
99.4 99.0 99.2	97.8 98.2 (mean) 98.0	-1.6 -0.8 -1.2	98.9 99.9 99.4	96.5 98.1 (mean) 97.3	-2.4 -1.8 -2.1

Table 4.8.3.8 Stability of Extracted Samples for tert-Butyl Acetate on SKC 575-002 Passive Samplers
punctured septa replaced			punctured septa retained
initial (%)	after one day (%)	difference (%)	initial (%)	after one day (%)	difference (%)
99.5 99.1 99.3	98.3 97.7 (mean) 98.0	-1.2 -1.4 -1.3	98.5 99.7 99.1	95.3 96.1 (mean) 95.7	-3.2 -3.6 -3.4

4.9 Interferences (sampling)

4.9.1 Charcoal tubes

Retention

The ability of a charcoal tube to retain the analyte after it has been collected was tested using test atmospheres having an average relative humidity of 80% RH at 23ºC. Separate test atmospheres were dynamically generated for each of the analytes. The concentrations of the test atmospheres were: n-Butyl Acetate (1435 mg/m³ or 302 ppm), sec-Butyl Acetate (1910 mg/m³ or 402 ppm), tert-Butyl Acetate (1930 mg/m³ or 406 ppm), and Isobutyl Acetate (1416 mg/m³ or 298 ppm). For each test atmosphere, six samplers had contaminated air (air with the analyte in it) drawn through them at 0.05 L/min for 60 min. Sampling was discontinued and three samples set aside. The generation system was flushed with contaminant-free air. Sampling resumed with the other three samples having contaminant-free air drawn through them at 0.05 L/min for 180 min and then all six samplers were analyzed. The mean recoveries for the samples in the second set divided by the first set were: 99.8% for n-Butyl Acetate, 99.9% for sec-Butyl Acetate, 100.4% for tert-Butyl Acetate, and 100.3% for Isobutyl Acetate.