Samples are collected by drawing a known volume of air through two
Anasorb 708 tubes connected in series. Samples are desorbed with
2 mL of methanol for 1 hour with shaking and analyzed by liquid
chromatography using an ultraviolet detector at 210 nm (LC-UV).
Recommended air volume and sampling rate:
24 L at 0.1 L/min
Reliable quantitation limit:
acrylic acid:
0.00301 ppm (0.00888 mg/m3)
methacrylic acid:
0.00475 ppm (0.0170 mg/m3)
Status of method:
Partially Evaluated Method. This method has been subjected to
established evaluation procedures, and is presented for information
and trial use.
Date: July, 1996
Chemist: Mary E. Eide
Organic Service Branch I
OSHA Salt Lake Technical Center
Salt Lake City, UT 84165-0200
1. General Discussion
1.1 Background
1.1.1 History
There is an OSHA validated method (28) for acrylic acid (Ref. 5.1) and a stop-gap
method for methacrylic acid (Ref. 5.2) which use two XAD-8 tubes connected in series
for sampling in the sampling train. SKC is no longer making XAD-8 tubes, and state that
Anasorb 708 tubes are the equivalent. The purpose of this study was to determine
whether the Anasorb 708 tubes could be substituted for the XAD-8 tubes. The
desorption, retention, and storage studies indicate that the Anasorb 708 tubes are a good
substitution for the XAD-8 tubes.
1.1.2 Toxic effects (This section is for information only and should not be taken as the basis
of OSHA policy.) (Ref. 5.3 and Ref. 5.4)
Acrylic acid is an acute irritant to skin, eyes, and mucous membranes. Acrylic acid is
readily adsorbed through the skin. Rats exposed to 300 ppm acrylic acid for 5
days/week for 4 weeks showed nose irritation, lethargy, and reduced weight gain. Mice
exposed to 75 ppm acrylic acid 6 hours/day 5 days/week for 13 weeks showed slight
degenerative lesions on the nasal mucous membranes. Methacrylic acid is a severe
contact irritant, and direct contact can cause blindness and skin ulceration. Rats
exposed to 300 ppm methacrylic acid for 20 days showed slight renal congestion. The
TLVs of 2 ppm for acrylic acid and 20 ppm for methacrylic acid were established at
these levels to prevent injury due to exposure to these compounds.
1.1.3 Workplace exposure (Ref. 5.3 and 5.4)
Acrylic acid and methacrylic acid are used as a monomers for the manufacture of resins
and polymers, and in organic syntheses. The U.S. production of acrylic acid and its
esters is about 500,000 tons per year.
1.1.4 Physical properties and other descriptive information (Ref. 5.5 and 5.6)
The analyte air concentrations throughout this method are based on the recommended sampling
and analytical parameters. Air concentrations listed in ppm are referenced to 25°C and 101.3 kPa
(760 mmHg).
1.2 Limit defining parameters
1.2.1 Detection limit of the overall procedure (DLOP)
The detection limit of the overall procedure for acrylic acid is 0.064 µg per sample
(0.001 ppm or 0.00267 mg/m3; and for methacrylic acid is 0.123 µg per sample (0.0015 ppm or
0.00513 mg/m3). This is the amount of analyte spiked on the sampler that will give a
response that is significantly different from the background response of a sampler blank.
The DLOP is defined as the concentration of analyte that gives a response (YDLOP) that is
significantly different (three standard deviations (SDBR)) from the background response
(YBR).
YDLOP - YBR = 3(SDBR)
The direct measurement of YBR and SDBR in chromatographic
methods is typically inconvenient, and difficult because YBR is usually extremely low.
Estimates of these parameters can be made with data obtained from the analysis of a series of samples
whose responses are in the vicinity of the background response. The regression curve
obtained for a plot of instrument response versus concentration of analyte will usually be
linear. Assuming SDBR and the precision of data about the curve
are similar, the standard error of estimate (SEE) for the regression curve can be substituted for
SDBR in the above in the above equation. The following calculations derive
a formula for the DLOP:
Yobs
=
observed response
Yest
=
estimated response from regression curve
n
=
total no. of data points
k
=
2 for a linear regression curve
At point YDLOP on the regression curve
YDLOP = A(DLOP) + YBR
A = analytical sensitivity (slope)
therefore
DLOP =
(YDLOP - YBR)A
Substituting 3(SEE) + YBR for YDLOP gives
DLOP =
3(SEE)A
The DLOP is measured as mass per sample and expressed as equivalent air concentrations,
based on the recommended sampling parameters. Ten samplers were
spiked with equal descending increments of analyte, such that the lowest sampler loading
was 0.2 µg/sample. This is the amount, when spiked on a sampler, that would produce a
peak approximately 10 times the background response for the 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 (A and SEE)
for the calculation of the DLOP. Values of 5157 and 109.9 were obtained for A and SEE
respectively for acrylic acid. The DLOP for acrylic acid was calculated to be
0.064 µg/sample (0.001 ppm). Values of 2838 and 116 were obtained for A and SEE
respectively for methacrylic acid. The DLOP for methacrylic acid was calculated to be
0.123 µg/sample (0.0015 ppm).
Table 1.2.1.1 Detection Limit of the Overall Procedure
for acrylic acid
mass per sample
area counts
(µg)
(µV-s)
0.2
2048
0.4
2732
0.6
3824
0.8
4865
1.0
6039
1.2
6890
1.4
8103
1.6
9069
1.8
10113
2.0
11127
Figure 1.2.1.1. Plot of data to determine the DLOP/RQL for acrylic acid.
Table 1.2.1.2 Detection Limit of the Overall Procedure
for methacrylic acid
mass per sample
area counts
(µg)
(µV-s)
0.2
1138
0.4
1427
0.6
1985
0.8
2724
1.0
3278
1.2
3730
1.4
4569
1.6
4910
1.8
5455
2.0
6122
Figure 1.2.1.2. Plot of data to determine the DLOP/RQL for methacrylic acid.
1.2.2 Reliable quantitation limit (RQL)
The reliable quantitation limit is 0.213 µg per sample for acrylic acid (0.00301 ppm), and
0.409 µg per sample for methacrylic acid (0.00475 ppm). This is the amount of
analyte spiked on a sampler that will give a signal that is considered the lower limit for
precise quantitative measurements.
The RQL is considered the lower limit for
precise quantitative measurements. It is determined from the regression line data
obtained for the calculation of the DLOP (Section 1.2.1 ), providing at least 75% of the
analyte is recovered. The RQL is defined as the concentration of analyte that gives
a response (YRQL) such that
YRQL - YBR = 10(SDBR)
therefore
RQL =
10(SEE)A
The RQL is the lowest loading at which 75% of the analyte, or more, can be recovered as determined
from the regression line of the plotted data.
Table 1.2.2.1 Reliable Quantitation Limit
mass per sample (µg)
mass recovered (µg)
recovery (%)
0.2
0.197
98.5
0.4
0.388
97.0
0.6
0.592
98.7
0.8
0.780
97.5
1.0
0.941
94.1
1.2
1.189
99.1
1.4
1.387
99.1
1.6
1.582
98.9
1.8
1.753
97.4
2.0
1.934
96.7
Figure 1.2.2.1 A chromatogram of the RQL for acrylic acid.
Table 1.2.2.2 Reliable Quantitation Limit
mass per sample (µg)
mass recovered (µg)
recovery (%)
0.2
0.196
98.0
0.4
0.396
99.0
0.6
0.592
98.7
0.8
0.772
96.5
1.0
0.998
99.8
1.2
1.188
99.0
1.4
1.340
95.7
1.6
1.534
95.9
1.8
1.787
99.3
2.0
1.974
98.7
Figure 1.2.2.2 A chromatogram of the RQL for methacrylic acid.
Figure 1.2.2.3 Plot of data to determine the RQL for acrylic acid.
Figure 1.2.2.4 Plot of data to determine the RQL for methacrylic acid.
2. Sampling Procedure
2.1 Apparatus
2.1.1 Samples are collected using a personal sampling pump calibrated, with the sampling
device attached, to within ±5% of the recommended flow rate.
2.1.2 Samples are collected with 7 cm × 4 mm i.d. × 6 mm o.d. glass sampling tubes packed with
one section of 100 mg of Anasorb 708 in series. The section is held in place with glass
wool plugs, in each tube. For this evaluation, commercially prepared sampling tubes were
purchased from SKC, Inc. (Fullerton, CA, catalog no. 226-30-8).
2.2 Technique
2.2.1 Immediately before sampling, break off the ends of the sampling tube. A sampling train
is assembled by connecting two tubes in series using the red plastic end cap, after the sealed
end has been cut off. A small piece of flexible plastic tubing may be substituted for the cut
red plastic end caps. The inside broken ends of the two Anasorb 708 tubes should be as
close together as possible, after the sampling train is assembled. All tubes should be from
the same lot.
2.2.2
Attach the sampling train to the pump with flexible tubing. It is desirable to utilize sampling
tube holders which have a protective cover to shield the employee from the sharp, jagged
end of the sampling tube.
2.2.3
Air being sampled should not pass through any hose or tubing before entering the sampling
train.
2.2.4
Attach the sampling train vertically with the outer tube pointing downward, in the worker's
breathing zone, and positioned so it does not impede work performance or safety.
2.2.5
After sampling for the appropriate time, remove the sample train and seal each tube with
intact plastic end caps. Wrap each tube separately end-to-end with a Form OSHA-21 seal.
2.2.6
Submit at least one blank sample with each set of samples. Handle the blank sampler in
the same manner as the other samples except draw no air through it.
2.2.7
Record sample volumes (in liters of air) for each sample, along with any potential
interferences.
2.2.8
Ship any bulk samples separate from the air samples.
2.2.9
Submit the samples to the laboratory for analysis as soon as possible after sampling. If
delay is unavoidable, store the samples in a refrigerator.
2.3 Desorption efficiency
2.3.1 The desorption efficiencies of acrylic acid were determined by liquid-spiking the Anasorb
708 tubes at loadings of 0.1 to 2 times the target concentration. The loadings on the tubes
were 8, 40, 80, and 160µg of acrylic acid. These samples were stored overnight at
ambient temperature and then opened, placed into 4 mL vials, desorbed with 2 mL
methanol for 1 hour on the shaker, and analyzed by LC-UV. The average desorption
efficiency over the studied range was 98.7%.
Table 2.3.1 Desorption Efficiency of Acrylic acid
Tube #
% Recovered
0.1 ×
0.5 ×
1.0 ×
2.0 ×
8 µg
40 µg
80 µg
160 µg
1
98.0
98.6
98.1
99.7
2
98.4
98.5
98.2
99.5
3
99.9
98.6
98.5
99.0
4
98.8
99.2
98.2
99.2
5
97.0
98.6
99.0
98.8
6
98.5
98.0
99.2
99.0
average
98.4
98.6
98.5
99.2
overall average
98.7
standard deviation
±0.629
2.3.2 The desorption efficiencies of methacrylic acid were determined by liquid-spiking the
Anasorb 708 tubes at loadings of 0.1 to 2 times the target concentration. The loadings on
the tubes were 71, 355, 711, and 1420 µg of methacrylic acid. These samples were
stored overnight at ambient temperature and then desorbed and analyzed. The average
desorption efficiency over the studied range was 98.6%.
Table 2.3.2 Desorption Efficiency of Methacrylic acid
Tube #
% Recovered
0.1 ×
0.5 ×
1.0 ×
2.0 ×
71 µg
355 µg
711 µg
1420 µg
1
96.9
98.9
98.3
98.7
2
99.1
99.6
98.8
98.7
3
98.0
98.8
98.7
98.3
4
97.8
98.0
98.8
99.2
5
98.0
97.2
98.6
101
6
99.2
98.1
98.9
98.5
average
98.2
98.4
98.7
99.1
overall average
98.6
standard deviation
±0.810
2.4 Retention efficiency
The sampling tubes were spiked at the 2 × PEL level, loadings of 160 µg acrylic acid and
1420 µg methacrylic acid, allowed to equilibrate 4 hours, and then had 24 L humid air
(81% RH at 21°C) pulled through them at 0.1 Lpm. They were opened, desorbed, and
analyzed by LC-UV. The retention efficiency averaged 98.9% for acrylic acid and 99.7%
for methacrylic acid. There was little or no acrylic and methacrylic acids found on the back
sections of the tubes.
Table 2.4.1 Retention Efficiency of Acrylic acid
Tube #
% Recovered
Front section
Back section
Total
1
99.9
0.0
99.9
2
98.6
0.1
98.7
3
100
0.0
100
4
97.1
0.3
97.4
5
98.6
0.2
98.8
6
98.4
0.1
98.5
average
98.9
Table 2.4.2 Retention Efficiency of Methacrylic acid
Tube #
% Recovered
Front section
Back section
Total
1
100
0.0
100
2
95.6
2.0
97.6
3
101
0.0
101
4
98.7
0.0
98.7
5
101
0.0
101
6
99.9
0.0
99.9
average
99.7
2.5 Sample storage
The front sections of twelve sampling tubes were each spiked with 80 µg acrylic acid and
711 µg methacrylic acid. Twelve more tubes were spiked at the same loadings and then had 24 liters of
humid air (81% RH at 22°C) drawn through them at 0.1 Lpm. Six samples from each group
were stored at room temperature (24°C) and the other six tubes stored at refrigerator
temperature (-4°C). Three samples of each type were analyzed after 7 days and the remaining
three samples of each type after 14 days. The amounts recovered, corrected for desorption efficiency,
indicate good storage stability for the time period studied and had an average recovery of 99.3% for all acrylic
acid conditions, and 99.4% for all methacrylic acid conditions.
Table 2.5.1 Storage Test for Acrylic acid
Time
% Recovery
% Recovery
% Recovery
% Recovery
(days)
Dry
Dry
Humid
Humid
Refrigerated
Ambient
Refrigerated
Ambient
7
100
100
99.9
99.8
7
99.6
99.9
100
99.1
7
99.2
99.3
98.0
99.0
14
98.8
100
98.1
99.6
14
99.9
99.2
99.8
98.2
14
99.2
99.5
99.0
97.0
average
99.5
99.7
99.1
98.8
Table 2.5.2 Storage Test for Methacrylic acid
Time
% Recovery
% Recovery
% Recovery
% Recovery
(days)
Dry
Dry
Humid
Humid
Refrigerated
Ambient
Refrigerated
Ambient
7
100
100
100
99.7
7
99.2
99.6
100
100
7
99.3
99.3
100
98.8
14
98.8
99.5
102
98.2
14
100
101
98.9
97.6
14
99.5
98.2
97.0
98.6
average
99.5
99.6
99.7
98.8
2.6 Recommended air volume and sampling rate.
Based on the data collected in this evaluation, 24 L air samples should be collected at a sampling
rate of 0.1 L/min.
2.7 Interferences (sampling)
2.7.1 It is not known if any compounds will severely interfere with the collection of acrylic and
methacrylic acid on the sampling tubes. In general, the presence of other contaminant
vapors in the air will reduce the capacity of the sampling tubes to collect acrylic and
methacrylic acid.
2.7.2 Suspected interferences should be reported to the laboratory with submitted samples.
2.8 Safety precautions (sampling)
2.8.1 Attach the sampling equipment to the worker in such a manner that it will not interfere
with work performance or safety.
2.8.2 Follow all safety practices that apply to the work area being sampled.
2.8.3 Wear eye protection should be worn when breaking the ends of the glass sampling tubes.
3. Analytical Procedure
3.1 Apparatus
3.1.1 The instrument used in this study was a liquid chromatograph equipped with an
ultraviolet detector, specifically a Waters 600 E pump and system controller, Waters 717
autosampler, and Waters 490 E programmable multiwavelength detector.
3.1.2 An LC column capable of separating the analyte from any interferences. The column used
in this study was a LC-8-DB column, 5µ film thickness, 25 cm long, 4.6 mm I.D.
3.1.3 An electronic integrator or some suitable method of measuring peak areas.
3.1.4 Four milliliter vials with TeflonTM-lined caps.
3.1.5 A 100 µL syringe or other convenient size for sample injection.
3.1.6 Pipets for dispensing the desorbing solution.
3.1.7 Volumetric flasks - 10 mL and other convenient sizes for preparing standards.
3.2 Reagents
3.2.1 Acrylic acid, Reagent grade.
3.2.2 Methacrylic acid, Reagent grade
3.2.3 Methanol, HPLC grade
3.2.4 Deionized water, the water used in this study was from a Millipore Milli-Q water
purification system.
3.2.5 Phosphoric acid, Reagent grade
3.2.6 Acetonitrile, HPLC grade
3.2.7 The mobile phase was 0.1:4:96 solution of phosphoric acid: acetonitrile: water.
3.3 Standard preparation
3.3.1 At least two separate stock standards are prepared by diluting a known quantity of acrylic
and methacrylic acids with methanol. The concentration of these stock standards was
1050 µg/mL acrylic acid and 1015 µg/mL methacrylic acid.
3.3.2 Dilutions of these stock standards were prepared to bracket the samples. The range of
the standards used in this study was from 1.05 to 1050 µg/mL acrylic acid and 1.015 to
1015 µg/mL methacrylic acid.
3.4 Sample preparation
3.4.1 Sample tubes are opened and the front and back section of each tube are placed in
separate 4 mL vials.
3.4.2 Each section is desorbed with 2 mL of methanol.
3.4.3 The vials are sealed immediately and allowed to desorb for 1 hour with constant shaking.
3.5 Analysis
3.5.1 Liquid chromatograph conditions.
Injection size:
10 µL
Column:
LC-8-DB, 5µ, 25cm, 4.6 mm I.D.
Mobile phase:
96% water 4% acetonitrile 0.1% phosphoric acid
Detector:
Waters 490 E programmable multiwavelength detector at 210 nm.
Figure 3.5 A chromatogram of an analytical standard of
105 µg/mL acrylic acid and 101.5 µg/mL methacrylic acid.
3.5.2 Peak areas are measured by an integrator or other suitable means.
3.6 Interferences (analytical)
3.6.1 Any compound that produces a 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 desorbed. Generally, chromatographic conditions can be
altered to separate an interference from the analyte.
3.6.2 When necessary, the identity or purity of an analyte peak may be confirmed by GC-mass
spectrometer or by another analytical procedure.
Figure 3.6.2.1 A mass spectrum of acrylic acid.
Figure 3.6.2.2 A mass spectrum of methacrylic acid.
Figure 3.6.2.3 An UV spectra of acrylic acid.
Figure 3.6.2.4 An UV spectra of methacrylic acid.
3.7 Calculations
3.7.1
The calibration curve was made from at least four standards at different concentrations
bracketing the samples.
3.7.2
The values for the air samples and blanks are obtained from the calibration curve.
3.7.3
Values (µg) obtained for blanks are subtracted from air samples.
3.7.4
To calculate the concentration of analyte in the air sample the following formulas are used:
(µg/m) (desorption volume)(desorption efficiency)
= mass of analyte in sample
(mass of analyte in sample)molecular weight
= number of moles of analyte
(number of moles of analyte)
(molar volume at 25°C & 760mm)
=
volume the analyte will occupy at 25°C & 760mm
(volume analyte occupies) (106)*(air volume)
= ppm
* All units must cancel.
3.7.5 The above equations can be consolidated to the following formula.
3.8.1 Avoid skin contact and inhalation of all chemicals.
3.8.2 Wear safety glasses, gloves and a lab coat at all times while in the laboratory areas.
4. Recommendations for Further Study
Collection studies should be performed from a dynamically generated test atmosphere.
5. References
5.1 Cummins, K., Method 28, "Acrylic Acid", Organic Methods Evaluation Branch, OSHA Salt
Lake Technical Center, 1981.
5.2 Eide, M., "Methacrylic Acid", Organic Service Branch I, OSHA Salt Lake Technical Center,
1988, OSHA SLTC in-house file.
5.3 Documentation of the Threshold Limit Values and Biological Exposure Indices, Fifth Edition,
American Conference of Governmental Industrial Hygienists Inc., Cincinnati, OH, 1986, p.14.1.
5.4 Documentation of the Threshold Limit Values and Biological Exposure Indices, Fifth Edition,
American Conference of Governmental Industrial Hygienists Inc., Cincinnati, OH, 1986, p.362.
5.5 Budavari, S., The Merck Index, Twelfth Edition, Merck & Co., Inc., Whitehouse Station NJ,
1996, p. 23.
5.6 Budavari, S., The Merck Index, Twelfth Edition, Merck & Co., Inc., Whitehouse Station NJ,
1996, p. 1015.