|
Method no.: |
88 |
|
|
Matrix: |
Air |
|
|
Target Concentration: |
1 ppm (2.4 mg/m3) and 20 ppm (47 mg/m3) |
|
|
Procedure: |
Samples are collected by drawing air through standard size Anasorb 747 adsorbent tubes.
The Anasorb 747 is desorbed with carbon disulfide and the desorbate is analyzed by gas
chromatography using a flame ionization detector. |
|
|
Recommended air volume and sampling rate: |
5 L at 0.1 L/min |
|
|
Standard error of estimate at target concentration: (Section 4.7.): |
5.7% (1 ppm) 6.5% (20 ppm) |
|
|
Special requirement: |
Stored samples should be kept at 0° or colder to reduce migration. Reduced temperature
shipment of samples to the laboratory is not necessary. |
|
|
Status of method: |
Evaluated method. This method has been subjected to the
established evaluation procedures of the Organic Methods Evaluation Branch. |
|
|
June 1991 |
Carl J. Elskamp |
|
|
Organic Methods Evaluation Branch
Industrial Hygiene Chemistry Division
OSHA Salt Lake Technical
Center
Sandy UT 84070-6406
|
1. General Discussion
1.1. Background
1.1.1. History
OSHA has set a time weighted average final rule limit of 20 ppm for workplace exposure to
propylene oxide. (Ref. 5.1.) Based on evidence that propylene oxide is an animal carcinogen,
NIOSH recommends that occupational exposure to propylene oxide be reduced to the lowest
feasible level. (Ref. 5.2.) Because the PEL for ethylene oxide, which is chemically similar to
propylene oxide and is also an animal carcinogen, has recently been reduced to 1 ppm
(Ref.5.3.), evaluation data was collected at 1 ppm (TC-1)
as well as 20 ppm (TC-20) to assure that an adequate monitoring procedure would
be available if the PEL for propylene oxide were significantly lowered in the future.
The current methodology used by OSHA to determine propylene oxide in air is based on the
coconut shell charcoal tube procedure evaluated by NIOSH. (Ref. 5.4.) The concentration
range studied was 50 to 200 ppm (5-L air samples) because the OSHA PEL was 100 ppm at
that time. The method specifies that samples be shipped at reduced temperatures, although no
sample stability tests were reported. Typically, air samples collected on adsorbent tubes are
shipped refrigerated to minimize migration of analyte from the front section to the back section
of adsorbent.
Preliminary tests at the 20-ppm level (5-L air samples) confirmed that migration was indeed a
problem. Test samples were prepared by spiking the front sections of SKC, Inc. Lot 120
coconut shell charcoal tubes and storing them at room temperature for six days.
Approximately 5 L of air at 80% relative humidity had been drawn through the charcoal tubes
before they were spiked. Upon analysis, about 20% of the original amount of propylene oxide
was found on the back sections. When added to the amount found on the front sections, the
total amount found was only about 80% of the original amount spiked. This not only indicated
that there is a migration problem but there may also be a stability problem for propylene oxide
collected on charcoal.
Commercially available glass sampling tubes containing a new carbon-based adsorbent called
Anasorb 747 were evaluated and found to be a superior alternative to charcoal sampling tubes.
Storage samples generated from humid atmospheres exhibited excellent storage stability over
the 15-day perious studied. Some minor migration of propylene oxide to the back section of
the sampling tubes for the TC-20 anbient storage samples was observed, but was not
considered significant enough to require shipment of samples to the laboratory at reduced temperatures.
1.1.2. Toxic effects (This section is for information only and should not be taken as the basis of OSHA policy.)
Propylene oxide is an irritant and a mild depressant of the central nervous system. Excessive
exposure may cause irritation of the eyes, nose, throat, and lungs. Contact with the liquid may
cause skin or eye irritation or burns. (Ref. 5.5.)
NIOSH has recently issued a Current Intelligence Bulletin on the carcinogenic effects of
exposure to propylene oxide. Numerous studies are cited that show propylene oxide exposure
produces cancer and benign tumors in both rats and mice. They conclude that propylene oxide
should be considered a potential occupational carcinogen and worker exposure should be
reduced to the lowest feasible levels. (Ref. 5.2.)
Currently OSHA has a transitional limit of 100 ppm and a final rule limit of 20 ppm for 8-hour
time weighted average exposures to airborne propylene oxide. (Ref. 5.1.)
1.1.3. Workplace exposure
Propylene oxide is produced by the chlorohydrin process, where propylene is reacted with
chlorine, or by the hydroperoxide process, where an organic hydroperoxide is used to
epoxidize propylene. The estimated U.S. production of propylene oxide in 1980 was 1,767
million pounds. It is used primarily as an intermediate for the manufacture of polyether
polyols in the production of polyurethane foams, and for the manufacture of propylene glycol
in the production of unsaturated polyester resins. Small quantities are also used for sterilizing
medical equipment and for fumigating foodstuffs. In 1983, NIOSH estimated that 209,000
U.S. workers were potentially exposed to propylene oxide. (Ref. 5.2.)
1.1.4. Physical properties (Ref. 5.5. unless otherwise noted)
| | |
structural formula: | |
CAS number: | 75-56-9 |
molecular weight: | 58.08 |
specific gravity (water=1): | 0.830 |
boiling point at 101.3 kPa(760 mmHg): | 34° |
melting point: | -112° |
vapor density (air = 1 at boiling point of propylene oxide): | 2 |
vapor pressure at 20°: | 58.9 kPa (442 mmHg) |
appearance: | colorless liquid |
odor: | etherlike |
evaporation rate (butyl acetate = 1): | 33.7 |
flash point (closed cup): | -37° |
autoignition temperature: | 748° |
flammable limits in air, % by volume: | 2.1 to 37.0 |
odor threshold: | 200 ppm |
solubility: | 59% by weight in water at 25°
miscible with acetone, benzene, carbon tetrachloride, ether, and methanol (Ref. 5.2.) |
synonyms: | 1,2-propylene oxide; epoxypropane;
1,2-epoxy-propane; 2,3-epoxypropane; ethylene oxide,
methyl-; methyl ethylene oxide; methyl oxirane; oxirane, methyl-;
NCI-C50099; oxyde de propylene (French); propene oxide; propylene epoxide;
propyleneoxide; propane, 1,2-epoxy-; propane, epoxy-; UN 1280
(Ref. 5.6.) |
The analyte air concentrations throughout this method are based on the recommended sampling and
analytical parameters. Air concentrations listed in ppm and ppb are referenced to 25° and 101.3 kPa (760 mmHg).
1.2. Limit defining parameters
1.2.1. Detection limit of the analytical procedure
The detection limit of the analytical procedure is 24 pg per injection. This is the amount of
propylene oxide that will produce a peak with a height approximately 5 times the height of
baseline noise. (Section 4.1.)
1.2.2. Detection limit of the overall procedure
The detection limit of the overall procedure is 0.415 µg per sample (35 ppb or
83 µg/m3).
This is the amount of propylene oxide spiked on an Anasorb 747 adsorbent tube that, upon
analysis, produces a peak similar in size to that of the detection limit of the analytical
procedure. (Section 4.2.)
1.2.3. Reliable quantitation limit
The reliable quantitation limit is 0.415 µg per sample (35 ppb or 83 µg/m3.
This is the smallest amount of propylene oxide that can be quantitated within the requirements
of a recovery of at least 75% and precision (±1.96 SD) of ±25% or better.
(Section 4.3.)
The reliable quantitation limit and detection limits reported in the method are based upon optimization
of the GC for the smallest possible amount of analyte. When the target concentration of an analyte is
exceptionally higher than these limits, they may not be attainable at the routine operating parameters.
1.2.4. Instrument response to the analyte
The instrument response over the concentration ranges of 0.5 to 2 times the TC-1
and TC-20 target concentrations is linear. (Section 4.4.)
1.2.5. Recovery
The recovery of propylene oxide from samples used in 15-day storage tests remained above
86% and 91% at the TC-1 and TC-20 levels respectively when the samples were stored at
ambient temperatures. (Section 4.5., from regression lines shown in Figures
4.5.1.2. and
4.5.2.2.)
1.2.6. Precision (analytical procedure)
The pooled coefficients of variation obtained from replicate injections of analytical standards at
0.5, 1 and 2 times the target concentrations are 0.013 and 0.012 at the TC-1 and TC-20 levels
respectively. (Section 4.6.)
1.2.7. Precision (overall procedure)
The precisions at the 95% confidence level for the refrigerated 15-day storage tests are
±11.2% and ±12.7% at the TC-1 and TC-20 levels respectively. These include an additional
±5% for pump error. The overall procedure must provide results at the target concentration
that are ±25% or better at the 95% confidence level. (Section 4.7.)
1.2.8. Reproducibility
Six samples for each target concentration collected from controlled test atmospheres and a draft
copy of this procedure were given to a chemist unassociated with this evaluation. The TC-1
and TC-20 samples were analyzed after 37 and 44 days of refrigerated storage respectively.
One of the TC-1 results was rejected as being an outlier by the Q test.
(Ref. 5.7.) None of the other sample results deviated from its
theoretical value by more than the precision reported in Section 1.2.7. (Section 4.8.)
1.3. Advantage
Reduced temperature shipment of samples to the laboratory is not necessary.
2. Sampling Procedure
2.1. Apparatus
2.1.1. Samples are collected using a personal sampling pump calibrated to within ±5% of the
recommended flow rate with a sampling tube in line.
2.1.2. Samples are collected with solid sorbent sampling tubes containing Anasorb 747. Each tube
consists of two sections of Anasorb 747 separated by a urethane foam plug. The front section
contains 140 mg and the back section, 70 mg. The sections are held in place with glass wool
plugs in a glass tube 4-mm i.d. x 70-mm length. For this evaluation, SKC Inc. Lot 645 tubes
(Catalog Number 226-81) were used.
2.2. Reagents
None required
2.3. Technique
2.3.1. Immediately before sampling, break off the ends of the Anasorb 747 tube. All tubes should be from the same lot.
2.3.2. Connect the sampling tube to the sampling pump with flexible tubing. It is desirable to utilize
sampling tube holders that have protective covers to shield the employee from the sharp,
jagged end of the sampling tube. position the tube so that sampled air passes through the 140-mg section first.
2.3.3. Air being sampled should not pass through any hose or tubing before entering the sampling tube.
2.3.4. To avoid channeling, place the sampling tube vertically in the employee's breathing zone.
2.3.5. After sampling, seal the tubes immediately with plastic caps and wrap lengthwise with OSHA Form 21.
2.3.6. Submit at least one blank sampling tube with each sample set. Blanks should be
handled in the same manner as samples, except no air is drawn through them.
2.3.7. Record sample volumes (in liters of air) for each sample.
2.3.8. List any compounds that could be considered potential interferences, especially solvents, that
are being used in the sampling area.
2.3.9. Ship any bulk sample(s) in a container separate from the air samples.
2.4. Sampler capacity
Sampler capacity is determined by measuring how much air can be sampled before breakthrough of
analyte occurs, i.e., the sampler capacity is exceeded. Breakthrough studies were performed by
monitoring the effluent from sampling tubes containing only the 140-mg section of Anasorb 747 while
sampling at 0.1 L/min from an atmosphere containing 40 ppm of propylene oxide. Breakthrough was
considered to occur when the propylene oxide concentration in the effluent was 5% of the upstream
concentration. The atmosphere was at approximately 80% relative humidity and 20-25°. The
average 5% breakthrough volume from three determinations was 11.1 L.
2.5. Desorption efficiency
2.5.1. The average desorption efficiency is 98.5% and 98.8% over the range of 0.5 to 2 times the
TC-1 and TC-20 levels respectively. (Section 4.9.)
2.5.2. Desorbed samples remain stable for at least 24 h. (Section 4.10.)
2.5.3. Desorption efficiencies should be periodically confirmed because differences may occur due to
variations in Anasorb 747, desorption solvent, and operator technique.
2.6. Recommended air volume and sampling rate
2.6.1. For TWA samples, the recommended air volume is 5 L collected at 0.1 L/min
(50-min samples). Although the break through volume was experimentally determined to exceed 11 L
(Section 2.4.), a recommended air volume of 5 L was chosen to assure that the method will
be valid over a wide range of sampling conditions.
2.6.2. For short-term samples, the recommended air volume is 5 L collected at 1.0 L/min (5-min samples).
2.7. Interferences (sampling)
2.7.1. It is not known if any compound(s) will severely interfere with the collection of propylene
oxide on Anasorb 747. In general, the presence of other solvent vapors in the sampled air wall
reduce the capacity of Anasorb 747 to collect propylene oxide.
2.7.2. Potential interferences used in the sampling area should be reported to the laboratory with each sample set.
2.8. Safety precautions (sampling)
2.8.1. Attach the sampling equipment to the employee so that it will not interfere with work
performance or safety. Use sample tube holders with protective covers whenever possible.
2.8.2. Wear eye protection when breaking the ends of the Anasorb 747 tubes.
2.8.3. Follow all safety procedures that apply to the work area being sampled.
3. Analytical Procedure
3.1. Apparatus
3.1.1. A GC equipped with a flame ionization detector. For this evaluation, a
Hewlett-Packard 5890 Series II Gas Chromatograph equipped with a 7673A Automatic Sampler was used.
3.1.2. A GC column capable of separating propylene oxide from the desorption solvent, internal
standard and any interferences. A thick film, 60-m x 0.32-mm i.d., fused silica
RTx-Volatiles column (Cat. no. 10904, Restek Corp., Bellefonte, PA) was used in this evaluation.
3.1.3. An electronic integrator or some other suitable means of measuring peak areas or heights. A
Waters 860 Networking Computer System was used in this evaluation.
3.1.4. Two-milliliter vials with Teflon-lined caps.
3.1.5. A dispenser capable of delivering 1.0 mL of desorption solvent to prepare standards and
samples. If a dispenser is not available, a 1.0-mL volumetric pipet may be used.
3.2. Reagents
3.2.1. Propylene oxide, reagent grade. Fisher scientific Lot 713390 propylene oxide was used in this evaluation.
3.2.2. Carbon disulfide, chromatographic grade. Omnisolv, glass distilled carbon disulfide from EM
Science was used in this evaluation.
3.2.3. A suitable internal standard, reagent grade. Benzene was used in this evaluation.
3.2.4. The desorption solvent consists of carbon disulfide containing an
internal standard at a concentration of 25 µL/L.
3.2.5. GC grade nitrogen, air, and hydrogen.
3.3. Standard preparation
3.3.1. Prepare concentrated stock standards by diluting the reagent grade
propylene oxide with carbon disulfide. Prepare working standards by injecting
microliter amounts of concentrated stock standards into vials containing 1.0 mL
of desorption solvent delivered from the same dispenser used to desorb samples.
For example, prepare a stock standard by diluting 3.00 mL of propylene oxide (sp
gr = 0.830) to 50.0 mL with carbon disulfide. This stock solution concentration
would equal 49.8 µg/L. A working standard of 239.0 µg/sample is prepared by
injecting 4.8 µL of this stock into a vial containing 1.0 mL of desorption
solvent.
3.3.2. Bracket sample concentrations with working standard concentrations. If samples fall outside of
the concentration range of prepared standards, prepare and analyze additional standards to
ascertain the linearity of response.
3.4. Sample preparation
3.4.1. Transfer each Anasorb 747 section of the samples to separate vials. Discard the glass tubes and plugs.
3.4.2. Add 1.0 mL of desorption solvent to each vial using the same dispenser as used for preparation of standards.
3.4.3. Immediately cap the vials and shake them periodically for about 10 min before analysis.
3.5. Analysis
3.5.1. GC conditions
| |
| |
column: |
60-m x 0.32-mm i.d. fused silica, RTx-Volatiles, thick film |
injection volume: |
1.0 µL (with a 17:1
split) |
zone temperatures: |
column- injector- detector- |
70° 200° 250° |
gas flows: |
hydrogen (carrier)- nitrogen (makeup)- hydrogen (flame)- air- |
3.7 mL/min (110 kPa head pressure) 22 mL/min 43 mL/min 400 mL/min |
retention times: |
propylene oxide- (benzene- 6.0 min) |
3.0 min |
chromatograms: |
Section
4.11 |
3.5.2. Peak areas (or heights) are measured by an integrator or other suitable means.
3.5.3. An internal standard (ISTD) calibration method is used. Calibration curves are prepared by
plotting micrograms of propylene oxide per sample versus ISTD-corrected response
of standard injections. Sample concentrations must be bracketed by standards.
3.6. Interferences (analytical)
3.6.1. Any compound that produces a flame ionization detector response and has a similar retention time
as propylene oxide or the internal standard is a potential interference. Any potential interferences
reported to the laboratory by the industrial hygienist should be considered before samples are desorbed.
3.6.2. GC parameters (i.e. column and column temperature) may be changed to possibly circumvent interferences.
3.6.3. Retention time on a single column is not considered proof of chemical identity. Confirmation
should be performed by GC/mass spectrometry or another suitable technique.
3.7. Calculations
The propylene oxide concentration for samples is obtained from the calibration curve in terms of
micrograms per sample, uncorrected for desorption efficiency. The air concentration is calculated using
the following formulae. The back (70-mg) section is analyzed primarily to determine if there was any
breakthrough from the front (140-mg) section during sampling. If a significant amount of analyte is found
on the back section (e.g., greater than 25% of the amount found on the front section), this fact should be
reported with sample results. If any analyte is found on the back section, it is added to the amount found
on the front section. This total amount is then corrected by subtracting the total amount (if any) found in
the corresponding blank sampling tube.
mg/m3 = |
(micrograms of analyte per sample, blank corrected)
(liters of air sampled)(desorption efficiency)
|
ppm = |
(mg/m3)(24.46) 58.08 |
= (mg/m3)(0.421)
|
where |
24.46 = molar volume (L) at 25° and 101.3 kPa (760 mmHg)
58.08 = molecular weight of propylene oxide
|
3.8. Safety precautions (analytical)
3.8.1. Avoid skin contact and inhalation of all chemicals.
3.8.2. Restrict the use of all chemicals to a fume hood then possible.
3.8.3. Wear safety glasses and a lab coat at all times while in the lab area.
4. Backup Data
4.1. Detection limit of the analytical procedure
The injection size listed in the analytical procedure (1.0 µL with a 17:1 split)
was used in the determination of the detection limit of the analytical
procedure. The detection limit of 24 pg was determined by making injections of a
415 pg/µL standard. This amount was judged to produce a peak with a height
approximately 5 times the baseline noise. A chromatogram of such an injection is
shown in
Figure 4.1.
4.2. Detection limit of the overall procedure
Six samples were prepared by injecting 0.415 µg (5.0 µL of a 0.083 µg/µL
standard) of propylene oxide into the 140-mg section of Anasorb 747
tubes. The detection limit of the overall procedure corresponds to an air
concentration of 35 ppb (83 µg/m3).
Table 4.2. Detection Limit of the Overall Procedure
|
sample no. | µg spiked |
µg recovered |
|
1 2 3 4 5 6 |
0.415 0.415 0.415 0.415 0.415 0.415 |
0.379 0.386 0.401 0.388 0.395 0.392 |
|
4.3. Reliable quantitation limit
The reliable quantitation limit was determined by analyzing Anasorb 747 tubes
that had been spiked with a loading equivalent to the detection limit of the
overall procedure. Samples were prepared by injecting 0.415 µg (5.0 µL of a
0.083 µg/L standard) of propylene oxide into the
140-mg section of Anasorb 747 tubes. This amount corresponds to an
air concentration of 35 ppb (83 µg/m3).
Table 4.3. Reliable Quantitation Limit (Based on samples and data of
Table 4.2)
|
sample no. | percent recovered | statistics |
|
1 2 3 4 5 6 |
91.3 93.0 96.6 93.5 95.2 94.5 |
X =
SD = Precision = = |
94.0 1.84 (1.96)(±1.84) ±3.61 |
|
4.4. Instrument response to the analyte
The instrument response to the analyte over the range of 0.5 to 2 times each target concentration was
determined from multiple injections of analytical standards. These data are given in Tables
4.4.1. and
4.4.2. and Figures 4.4.1. and 4.4.2.
The response is linear with slopes (in ISTD-corrected area counts per microgram
of analyte per sample) of 278.9 and 280.2 for the TC-1 and TC-20 levels respectively.
Table 4.4.1. Instrument Response
|
x TC-1 µg/sample ppm |
0.5x 5.976 0.503 |
1x 11.95 1.01 |
2x 23.90 2.01 |
|
area counts |
1716 1703 1714 1651 1729 1692 |
3426 3383 3467 3368 3376 3389 |
6742 6717 6813 6684 6656 6633 |
X |
1701 |
3402 |
6708 |
|
Table 4.4.2. Instrument Response
|
x TC-20 µg/sample ppm |
0.5x 119.5 10.1 |
1x 239.0 20.1 |
2x 478.1 40.3 |
|
area counts |
34508 34113 34482 34083 34174 33508 |
67259 66119 67717 67721 68350 66971 |
132472 133973 132993 136494 136590 134849 |
X | 34145 | 67356 | 134562 |
|
4.5. Storage test
Thirty-six samples were generated at each target concentration by sampling from atmospheres that were
at ambient temperature and approximately 80% relative humidity. Samples were collected for 50 min at
0.1 L/min (5-L samples). For each set of 36 samples for each target concentration, six samples were
analyzed immediately after generation, fifteen were stored in a refrigerator at 0° and
fifteen were stored in a closed drawer at ambient temperatures of 21-25°. Six samples, three from
refrigerated and three from ambient storage, were analyzed at intervals over a period of fifteen days. The
results are given in Tables 4.5.1. and
4.5.2. and shown graphically in
Figures
4.5.1.1.,
4.5.1.2.,
4.5.2.1.
and
4.5.2.2. After nine days of ambient temperature storage of the
TC-20 samples, approximately 1% of the collected propylene oxide was found on
the back sections. Similarly, approximately 2% and 4% was found on the back sections of the
twelve- and fifteen-day ambient storage samples respectively There was
no observed migration of propylene oxide for the refrigerated TC-20 samples or any of the TC-1 samples.
Table 4.5.1. Storage Test at TC-1
|
storage time | % recovery |
(days) | (refrigerated) | | (ambient) |
|
0 0 3 6 9 12 15 |
89.2 90.5 92.8 85.8 86.8 87.4 94.2 |
87.6 87.4 90.8 84.7 88.2 85.8 92.0 |
91.2 90.4 92.7 85.0 90.0 87.4 89.5 |
|
89.2 90.5 92.6 87.9 89.2 85.6 87.7 |
87.6 87.4 92.6 86.1 87.1 84.2 87.3 |
91.2 90.4 93.5 86.2 86.7 82.6 88.2 |
|
Table 4.5.2. Storage Test at TC-20
|
storage time | % recovery |
(days) | (refrigerated) | | (ambient) |
|
0 0 3 6 9 12 15 |
100.1 98.8 93.6 102.0 90.9 95.8 91.5 |
99.8 98.6 94.7 96.7 87.5 96.2 90.9 |
103.6 99.7 91.5 99.8 87.8 100.8 92.8 |
|
100.1 98.8 91.1 98.2 91.3 100.6 93.4 |
99.8 98.6 92.1 95.7 90.1 96.8 88.8 |
103.6 99.7 91.6 96.5 87.4 94.8 90.2 |
|
4.6. Precision (analytical Procedure)
The precision of tide analytical procedure is the pooled coefficient of variation determined from replicate injections
of standards. The precision of the analytical Procedure for each target concentration is given in
Tables 4.6.1. and
4.6.2. These tables are based on the data Presented in
Section 4.4.
Table 4.6.1. Precision of the Analytical Procedure at 0.5 to 2 times TC-1 (Based on
Table 4.4.1.)
|
x TC-1 µg/sample ppm |
0.5x 5.976 0.503 |
1x 11.95 1.01 |
2x 23.90 2.01 |
|
SD (area counts) CV
CV = 0.013 |
27.4 0.0161 | 37.8 0.0111 | 65.1 0.0097 |
|
Table 4.6.2. Precision of the Analytical Procedure at 0.5 to 2 times TC-20 (Based on
Table 4.4.2.)
|
x TC-20 µg/sample ppm |
0.5x 119.5 10.1 |
1x 239.0 20.1 |
2x 478.1 40.3 |
|
SD (area counts) CV
CV = 0.012 |
362.4 0.0106 | 766.7 0.0114 | 1738.1 0.0129 |
|
4.7. Precision (overall procedure)
The precision of the overall procedure is determined from the storage data. The determination of the
standard error of estimate (SEE) for a regression line plotted through the graphed storage data allows the
inclusion of storage time as one of the factors affecting overall precision. The SEE is similar to the
standard deviation, except it is a measure of dispersion of data about a regression line instead of about a
mean. It is determined with the following equation:
SEE = |
[ |
Ó(Yobs - Yest)2 |
] |
1/2 |
where |
n =
k =
k = |
total no. of data points
2 for linear regression
3 for quadratic regression |
|
Yobs = |
observed % recovery at a given time |
|
Yest = |
estimated % recovery from the regression line at the same given time |
|
|
|
|
n - k |
|
An additional 5% for pump error is added to the SEE by the
addition of variances. The SEEs are 5.7% and 6.5% at the TC-1 and
TC-20 levels respectively. The precision of the overall procedure is the
precision at the 95% confidence level, which is obtained by multiplying the SEE
(with pump error included) by 1.96 (the z-statistic from the
standard normal distribution at the 95% confidence level). The 95% confidence
intervals are drawn about their respective regression lines in the storage
graphs The precisions of the overall procedure are ±11.2% and ±12.7% at the
TC-1 and TC-20 levels respectively. The SEE and precision of
the overall procedure for each level were obtained from Figures
4.5.1.1. and
4.5.2.1.
4.8. Reproducibility
Six samples collected for each target concentration from controlled test
atmospheres (at about 80% R.H.,
23-24°, 86-88 kPa) were analyzed by a chemist
unassociated with this evaluation. The samples were generated by drawing the
test atmospheres through sampling tubes for 50 min at approximately 0.1 L/min.
The TC-1 and TC-20 samples were stored in a
refrigerator for 37 and 44 days respectively before being analyzed. About
2-3% of the total amount of anlyte found was on the back sections
of the TC-20 samples. Sample number 4 at the TC-1
level was rejected as being an outlier by the Q test. (Ref.
5.7.)
Table 4.8.1. Reproducibility at the TC-1
Level
|
sample no. | µg found |
µg expected | % found | % deviation |
|
1 2 3 4 5 6 |
10.87 11.02 11.50 9.47 10.79 11.00 |
11.18 11.06 11.27 10.88 10.73 10.95 |
97.2 99.6 102.0 87.0 100.6
100.5 |
-2.8 -0.4 +2.0 -13.0 +0.6 +0.5 |
|
Table 4.8.2. Reproducibility at the TC-20
Level
|
sample no. | µg found |
µg expected | % found | % deviation |
|
1 2 3 4 5 6 |
216.2 215.0 218.4 208.6 212.0 218.8 |
227.1 224.4 227.1 224.1 224.3 228.7 |
95.2 95.8 96.2 93.1 94.5 95.7 |
-4.8 -4.2 -3.8 -6.9 -5.5 -4.3 |
|
4.9. Desorption efficiency
The desorption efficiency over the range of 0.5 to 2 times each target
concentration was determined by injecting microliter amounts of stock standards
into the front section of Anasorb 747 tubes.
Table 4.9. Desorption Efficiency Data
|
level |
TC-1
| |
TC-20
|
x target concn µg/sample ppm |
0.5x 5.976 0.503 |
1x 11.95 1.01 |
2x 23.90 2.01 |
|
0.5x 119.5 10.1 |
1x 239.0 20.1 |
2x 478.1 40.3 |
|
desorption efficiency, % |
97.7 98.5 102.3 101.1 99.8 97.0 |
97.8 98.6 98.6 97.8 98.0 97.7 |
98.5 97.8 97.5 97.9 97.7 98.4 |
|
98.7 97.4 97.0 96.1 95.3 98.2 |
97.1 99.0 98.7 96.7 99.0 99.4 |
100.0 101.8 102.5 102.3 103.3 95.1 |
X |
99.4 | 98.1 |
98.0 | | 97.1 |
98.3 | 100.8 |
X |
98.5 | |
98.8 |
|
4.10. Stability of desorbed samples
The stability of desorbed samples was checked by reanalyzing the target
concentration samples from
Section 4.9.
one day later using fresh standards. The sample vials were resealed with new
septa after the original analyses and were allowed to stand at room temperature
until reanalyzed.
Table 4.10. Stability of Desorbed Samples at the
Target Concentrations
|
| % desorption after 24 h
|
sample no. | TC-1 |
TC-20 |
|
1 2 3 4 5 6 |
92.9 95.0 94.3 94.3 94.8 94.5 |
97.8 98.6 96.9 96.4 95.1 98.9 |
X |
94.3 | 97.3 |
|
4.11. Chromatograms
Chromatograms at each target concentration are shown in Figures
4.11.1. and
4.11.2. The
chromatograms are from injections of standards equivalent to 5-L
air samples at the target concentrations.
Figure 4.1. Detection limit
chromatogram. Key: (1) propylene oxide (2) benzene.
Figure 4.4.1. Instrument response to
propylene oxide over the 0.5 to 2 times the TC-1 range.
Figure 4.4.2. Instrument response to
propylene oxide over the 0.5 to 2 times the TC-20 range.
Figure 4.5.1.1. TC-1 refrigerated
storage samples.
Figure 4.5.1.2. TC-1
ambient storage samples.
Figure 4.5.2.1. TC-20 refrigerated storage
samples.
Figure 4.5.2.2. TC-20
ambient storage samples.
Figure 4.11.1. Chromatogram
of a standard at the TC-1 target concentration. Key: (1) propylene oxide (2)
benzene.
Figure 4.11.2. Chromatogram
of a standard at the TC-20 target concentration. Key: (1) propylene oxide (2)
benzene.
5. References
5.1. "Code of Federal Regulations", 29 CFR 1910.1000, Table
Z-1-A.-Limits for Air Contaminants, U.S. Government Printing Office,
Washington, DC, 1990.
5.2. "NIOSH Current Intelligence Bulletin 51: Carcinogenic
Effects of Exposure to Propylene Oxide", U.S. Department of Health and Human
Services, Public Health Service, Centers for Disease Control, National Institute
for Occupational Safety and Health, Publications Dissemination, DSDTT;
Cincinnati, OH, 1989, Publ. No. 89-111.
5.3. "Code of Federal Regulations", 29 CFR 1910.1047,
Ethylene Oxide, U.S. Government Printing Office, Washington, DC, 1990.
5.4."NIOSH Manual of Analytical Methods", 3rd ed. Vol. 2;
U.S. Department of Health and Human Services, Public Health Service, Centers for
Disease Control, National Institute for Occupational Safety and Health, Division
of Physical Sciences and Engineering; Cincinnati, OH, 1985, Method 1612, DHHS
(NIOSH).
5.5. "Occupational Health Guidelines for Chemical Hazards",
NIOSH/OSHA, Jan. 1981, DHHS (NIOSH) Publ. No. 81-123.
5.6. "Registry of Toxic Effects of Chemical Substances",
1985-86 ed. Vol. 4; U.S. Department of Health and Human Services, Public
Health Service, Centers for Disease Control, National Institute for Occupational
Safety and Health, U.S. Government Printing Office, Washington, DC, 1987.
5.7. Miller, J. C.; Miller, J. N. "Statistics for Analytical
Chemistry", Ellis Horwood Limited: Chichester, England, 1984, p 59-62.
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