ACRYLIC ACID
METHACRYLIC ACID

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)

Acrylic acid
Synonyms: CAS number: IMIS: RTECS: DOT: Molecular weight: Flash point: Boiling point: Melting point: Odor: Odor threshold: Color: Autoignition temperature: Density: Molecular formula: Structural formula:	Acroleic acid; Ethylene carboxylic acid; Propene acid; Propenoic acid; Vinyl formic acid 79-10-7 0117 AS4375000 UN 2218 corrosive liquid 72.06 68°C (155°F)(oc) 141°C 14°C acrid 1 ppm colorless liquid 238°C (820°F) 1.05204 (g/mL) C3H4O2
Methacrylic acid
Synonyms: CAS number IMIS: RTECS: DOT: Molecular weight: Flash point: Boiling point: Melting point: Odor: Color: Autoignition temperature: Density: Molecular formula: Structural formula:	alpha-Methacrylic acid; 2-Methylenepropionic acid; 2-Methylpropenoic acid; 2-Methyl-2-propenoic acid 79-41-4 M339 OZ2975000 UN2531 corrosive liquid 86.09 76°C (170°F)(coc) 163°C 15°C acrid, like acetic acid colorless to pale yellow liquid 435°C (815°F) 1.0153254 (g/mL) C4H6O2

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 (Y_DLOP) that is significantly different (three standard deviations (SD_BR)) from the background response (Y_BR).

Y_DLOP - Y_BR = 3(SD_BR)

The direct measurement of Y_BR and SD_BR in chromatographic methods is typically inconvenient, and difficult because Y_BR 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 SD_BR and the precision of data about the curve are similar, the standard error of estimate (SEE) for the regression curve can be substituted for SD_BR 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 Y_DLOP on the regression curve

YDLOP = A(DLOP) + YBR

A = analytical sensitivity (slope)

therefore

DLOP =

(YDLOP - YBR) A

Substituting 3(SEE) + Y_BR for Y_DLOP 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 (Y_RQL) such that

Y_RQL - Y_BR = 10(SD_BR)

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 Teflon^TM-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.

(µg/mL)(DV)(24.46)(106)(g)(mg) (24 L)(DE)(MW)(1000mg)(1000µg)

= ppm

µg/mL	= concentration of analyte in sample or standard
24.46	= Molar volume (liters/mole) at 25°C and 760 mm
MW	= Molecular weight (g/mole)
DV	= Desorption volume
24 L	= 24 liter air sample
DE	= Desorption efficiency

3.8 Safety precautions (analytical)

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.