Appendix D Sampling and Analytical Methods for Benzene Monitoring and Measurement Procedures
8 CA ADC § 5218 App. DBarclays Official California Code of Regulations
8 CCR § 5218 App. D
Appendix D Sampling and Analytical Methods for Benzene Monitoring and Measurement Procedures
Measurements taken for the purpose of determining employee exposure to benzene are best taken so that the representative average 8-hour exposure may be determined from a single 8-hour sample or two (2) 4-hour samples. Short-time interval samples (or grab samples) may also be used to determine average exposure level if a minimum of five measurements are taken in a random manner over the 8-hour work shift. Random sampling means that any portion of the workshift has the same chance of being sampled as any other. The arithmetic average of all such random samples taken on one work shift is an estimate of an employee's average level of exposure for that work shift. Air samples should be taken in the employee's breathing zone (air that would most nearly represent that inhaled by the employee). Sampling and analysis must be performed with procedures meeting the requirements of the standard.
There are a number of methods available for monitoring employee exposures to benzene. The sampling and analysis may be performed by collection of the benzene vapor on charcoal absorption tubes, with subsequent chemical analysis by gas chromatography. Sampling and analysis may also be performed by portable direct reading instruments, real-time continuous monitoring systems, passive dosimeters or other suitable methods. The employer has the obligation of selecting a monitoring method which meets the accuracy and precision requirements of the standard under his unique field conditions. The standard requires that the method of monitoring must have an accuracy, to a 95 percent confidence level, of not less than plus or minus 25 percent for concentrations of benzene greater than or equal to 0.5 ppm.
The OSHA Laboratory modified NIOSH Method S311 and evaluated it at a benzene concentration of 1 ppm. A procedure for determining the benzene concentration in bulk material samples was also evaluated. This work, reported in OSHA Laboratory Method No. 12, includes the following two analytical procedures:
Analyte: Benzene
Matrix: Air
Procedure: Adsorption on charcoal, desorption with carbon disulfide, analysis by GC.
Detection limit: 0.04 ppm
Recommend air volume and sampling rate: 10 L at 0.2 L/min.
3.2. Charcoal tubes: Glass with both ends flame sealed, 7cm long with a 6-mm O.D. and a 4-mm I.D., containing 2 sections of 20/40 mesh activated charcoal separated by a 2-mm portion of urethane foam. The activated charcoal is prepared from coconut shells and is fired at 600°C prior to packing. The adsorbing section contains 100 mg of charcoal, the back-up section 50 mg. A 3-mm portion of urethane foam is placed between the outlet and of the tube and the back-up section. A plug of silanized glass wool is placed in front of the adsorbing section. The pressure drop across the tube must be less than one inch of mercury at flow rate of 1 liter per minute.
Heat under reflux for 2 to 3 hours, 500 mL of carbon disulfide, 10 mL concentrated sulfuric acid, and 5 drops of concentrated nitric acid. The benzene is converted to nitrobenzene. The carbon disulfide layer is removed, dried with anhydrous sodium sulfate, and distilled. The recovered carbondisulfide should be benzene free. (It has recently been determined that benzene can also be removed by passing the carbon disulfide through 13x molecular sieve.)
4.4. Desorbing reagent. The desorbing reagent is prepared by adding 0.05 mL of p-cymene per milliliter of carbon disulfide. (The internal standard offers a convenient means of correcting analytical response for slight inconsistencies in the size of sample injections. If the external standard technique is preferred, the internal standard can be eliminated).
4.5. Purified GC grade helium, hydrogen and air.
5.4.1. Preparation of samples. In preparation for analysis, each charcoal tube is scored with a file in front of the first section of charcoal and broken open. The glass wool is removed and discarded. The charcoal in the first (larger) section is transferred to a 2-mL vial. The separating section of foam is removed and discarded; the second section is transferred to another capped vial, these two sections are analyzed separately.
5.4.2. Desorption of samples. Prior to analysis, 1.0 mL of desorbing solution is pipetted into each sample container. The desorbing solution consists of 0.05 uL internal standard per mL of carbon disulfide. The sample vials are capped as soon as the solvent is added. Desorption should be done for 30 minutes with occasional shaking.
5.5.1. Importance of determination. The desorption efficiency of a particular compound can vary from one laboratory to another and from one lot of chemical to another. Thus, it is necessary to determine, at least once, the percentage of the specific compound that is removed in the desorption process, provided the same batch of charcoal is used.
5.5.2. Procedure for determining desorption efficiency. The reference portion of the charcoal tube is removed. To he remaining portion, amounts representing 0.5X, 1X, and 2X (X represents target concentration) and based on a 10 L air sample are injected into several tubes at each level. Dilutions of benzene with carbon disulfide are made to allow injection of measurable quantities. These tubes are then allowed to equilibrate at least overnight. Following equilibration they are analyzed following the same procedure as the samples. Desorption efficiency is determined by dividing the amount of benzene found by amount spiked on the tube.
mg/m3 = (A)(B)/(C)(D)
Where: A = ug/mL benzene, obtained from the calibration curve,
B = desorption volume (1 mL),
C = liters of air sampled, and
D = desorption efficiency.
The concentration in mg/m3 can be converted to ppm (at 25°C and 760 mm) with the following equation: ppm = (mg/m3)(24.46)/(78.11)
Where: 24.46 = molar volume of an ideal gas at 25°C and 760 mm, and 78.11 = molecular weight of benzene.
The detection limit for the analytical procedure is 1.28 ng with a coefficient of variation of 0.023 at this level. This would be equivalent to a concentration of 0.04 ppm for a 10 L air sample. This amount provided a chromatographic peak that could be identifiable in the presence of possible interferences. The detection limit data were obtained by making 1 uL injections of a 1.283 ug/mL standard.
Injection | Area Count |
1 | 655.4 | |||
2 | 617.5 | |||
3 | 662.0 | X = 640.2 | ||
4 | 641.1 | SD = 14.9 | ||
5 | 636.4 | CV = 0.023 | ||
6 | 629.2 |
8.2. Pooled coefficient of variation--Air Samples. The pooled coefficient of variation for the analytical procedure was determined by 1 uL replicate injections of analytical standards. The standards were 16.04, 32.08, and 64.16 ug/mL, which are equivalent to 0.5, 1.0, and 2.0 ppm for a 10 L air sample respectively.
Injection | Area Counts |
0.5 ppm | 1.0 ppm | 2.0 ppm |
1 | 3996.5 | 8130.2 | 16481 | ||
2 | 4059.4 | 8235.6 | 16493 | ||
3 | 4052.0 | 8307.9 | 16535 | ||
4 | 4027.2 | 8263.2 | 16609 | ||
5 | 4046.8 | 8291.1 | 16552 | ||
6 | 4137.9 | 8288.8 | 16618 | ||
1 | 3996.5 | 8130.2 | 16481 | ||
2 | 4059.4 | 8235.6 | 16493 | ||
3 | 4052.0 | 8307.9 | 16535 | ||
4 | 4027.2 | 8263.2 | 16609 | ||
5 | 4046.8 | 8291.1 | 16552 | ||
6 | 4137.9 | 8288.8 | 16618 |
X = | 4053.3 | 8254.0 | 16548.3 |
SD = | 47.2 | 62.5 | 57.1 |
CV = | 0.0116 | 0.0076 | 0.0034 |
CV = 0.008 |
Samples were generated at 1.03 ppm benzene at 80% relative humidity, 20°C, and 643mm. All samples were taken for 50 minutes at 0.2 L/min. Six samples were analyzed immediately and the rest of the samples were divided into two groups by fifteen samples each. One group was stored at refrigerated temperature of -25°C, and the other group was stored at ambient temperature (approximately 23°C). These samples were analyzed over a period of fifteen days. The results are tabulated below.
PERCENT RECOVERY |
Day Analyzed | Refrigerated | Ambient |
0 | 97.4 | 98.7 | 98.9 | 97.4 | 98.7 | 98.9 | ||
0 | 97.1 | 100.6 | 100.9 | 97.1 | 100.6 | 100.9 | ||
2 | 95.8 | 96.4 | 95.4 | 95.4 | 96.6 | 96.9 | ||
5 | 93.9 | 93.7 | 92.4 | 92.4 | 94.3 | 94.1 | ||
9 | 93.6 | 95.5 | 94.6 | 95.2 | 95.6 | 96.6 | ||
13 | 94.3 | 95.3 | 93.7 | 91.0 | 95.0 | 94.6 | ||
15 | 96.8 | 95.8 | 94.2 | 92.9 | 96.3 | 95.9 |
Samples were prepared by injecting liquid benzene onto the A section of charcoal tubes. Samples were prepared that would be equivalent to 0.5, 1.0, and 2.0 ppm for a 10 L air sample.
PERCENT RECOVERY |
Sample | 0.5 ppm | 1.0 ppm | 2.0 ppm |
1 | 99.4 | 98.8 | 99.5 | ||||
2 | 99.5 | 98.7 | 99.7 | ||||
3 | 99.2 | 98.6 | 99.8 | ||||
4 | 99.4 | 99.1 | 100.0 | ||||
5 | 99.2 | 99.0 | 99.7 | ||||
6 | 99.8 | 99.1 | 99.9 |
X = | 99.4 | 98.9 | 99.8 |
SD = | 0.22 | 0.21 | 0.18 |
CV = | 0.0022 | 0.0021 | 0.0018 |
X = 99.4 |
Carbon disulfide from a number of sources was analyzed for benzene contamination. The results are given in the following table. The benzene contaminant can be removed with the procedures given in section 4.1.
Analyte: Benzene.
Sample | ppm equivalent ug Benzene/ml | (for 10 L air sample) |
Aldrich Lot 83017 | 4.20 | 0.13 | ||
Baker Lot 720364 | 1.01 | 0.03 | ||
Baker Lot 822351 | 1.01 | 0.03 | ||
Mallinkrodt Lot WEMP | 1.74 | 0.05 | ||
Mallinkrodt Lot WDSJ | 5.65 | 0.18 | ||
Mallindrodt Lot WHGA | 2.90 | 0.09 |
Treated SC 2 |
Matrix: Bulk Samples.
Procedure: Bulk samples are analyzed directly by high performance liquid chromatography (HPLC).
Detection limits: 0.01% by volume.
The typical operating conditions for the high performance liquid chromatograph are:
Since the integrator is programmed to report results in % benzene by volume in an undiluted sample, the following equation is used:
% Benzene by Volume = A x B
Where: A = % by volume on report, and
B = Dilution factor
(B = 1 for undiluted sample).
The detection limit for the analytical procedure for bulk samples is 0.88 ug, with a coefficient of variation of 0.019 at this level. This amount provided a chromatographic peak that could be identifiable in the presence of possible interferences. The detection limit data were obtained by making 10 uL injections of a 0.10% by volume standard.
1 | 45386 | |
2 | 44214 | |
3 | 43822 | X = 44040.1 |
4 | 44062 | SD = 852.5 |
6 | 42724 | CV = 0.019 |
AREA COUNT (PERCENT) |
Injection | 0.01 | 0.02 | 0.04 | 0.10 | 1.0 | 2.0 |
1 | 45386 | 84737 | 166097 | 448497 | 4395380 | 9339150 | |
2 | 44241 | 84300 | 170832 | 441299 | 4590800 | 9484900 | |
3 | 43822 | 83835 | 164160 | 443719 | 4593200 | 9557580 | |
4 | 44062 | 84381 | 164445 | 444842 | 4642350 | 9677060 | |
5 | 44006 | 83012 | 168398 | 442564 | 4646430 | 9766240 | |
6 | 42724 | 81957 | 173002 | 443975 | 4646260 | .......... | |
X = | 44040.1 | 83703.6 | 167872 | 444149 | 4585767 | 9564986 | |
SD = | 852.5 | 1042.2 | 3589.8 | 2459.1 | 96839.3 | 166233 | |
CV = | 0.0194 | 0.0125 | 0.0213 | 0.0055 | 0.0211 | 0.0174 | |
CV = | 0.017 |
Credits
Note: Authority cited: Sections 142.3, 9020, 9030 and 9040, Labor Code. Reference: Sections 142.3, 9004(d), 9009, 9020, 9030, 9031 and 9040, Labor Code.
History
1. New section 5218 and Appendices A-E filed 4-20-90; operative 5-20-90 (Register 90, No. 23).
This database is current through 6/21/24 Register 2024, No. 25.
Cal. Admin. Code tit. 8, § 5218 App. D, 8 CA ADC § 5218 App. D
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