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TOLUENE
Method number:
Matrix:
Target concentration: OSHA PEL: ACGIH TLV:
Procedure:
Recommended sampling parameters:
Adsorbent tubes Sampling rate: Sampling time: Diffusive samplers Exposure time:
Reliable quantitation limit: (240-min samples)
Standard error of estimate at: TWA: (240 min) Ceiling: (10 min) Peak: (1 min)
Air
TWA
200 ppm (753 mg/m^3 ) 200 ppm (753 mg/m^3 ) 50 ppm (188 mg/m^3 )
Ceiling (10 min) Peak 300 ppm (1130 mg/m^3 ) 500 ppm (1883 mg/m^3 ) 300 ppm (1130 mg/m^3 ) 500 ppm (1883 mg/m^3 ) none none
Adsorbent tube samples are collected by drawing workplace air through either coconut shell charcoal or Anasorb 747 tubes with personal sampling pumps. Diffusive samples are collected by exposing either 3M 3520 Organic Vapor Monitors (OVMs) or SKC 575-002 Passive Samplers to workplace air. Samples are desorbed with 60/40 (v/v) N,N -dimethylformamide/carbon disulfide (DMF/CS 2 ) and analyzed by gas chromatography using a flame ionization detector.
TWA Samples
50 mL/min <240 min
<240 min
Ceiling Samples
50 mL/min
10 min
10 min
Charcoal Tubes Anasorb 747 Tubes 3M 3520 OVMs
18.1 ppb 25.4 ppb 82 ppb
(68.3 μ g/m^3 ) (95.5 μ g/m^3 ) (309 μ g/m^3 )
Peak Samples
50 mL/min :1 min
Not Recommended
SKC 575-002 Samplers
224 ppb
(844 μ g/m^3 )
*For samples where sampling site atmospheric pressure and temperature are known. When either or both of these values are unknown, see Section 4.6 for applicable standard errors of estimate.
Status of method: Evaluated method. This method has been subjected to the established evaluation procedures of the Organic Methods Evaluation Branch.
Date: April 1998 Chemist: Carl J. Elskamp
Organic Methods Evaluation Branch OSHA Salt Lake Technical Center Salt Lake City, UT 84115-
- General Discussion
1.1 Background
1.1.1 History
The determination of toluene in air has consistently been one of the top analyses performed at the OSHA Salt Lake Technical Center (SLTC) for the last 25 years. It is based on a pioneering method developed by Otterson and Guy to determine airborne solvent vapors. (Ref. 5.1) Samples were collected by drawing air through glass tubes packed with 4 inches of 20/40 mesh activated charcoal, then desorbed with an appropriate solvent and analyzed by GC. Further developmental work was done to incorporate a flame-sealed tube containing two 1-inch sections of activated charcoal. (Ref. 5.2) Procedures for a multitude of solvents were subsequently evaluated through NIOSH based on a standardized “NIOSH charcoal tube” consisting of two sections of coconut shell activated charcoal contained in a 7-cm flame sealed glass tube. The front section contains 100 mg and the back section 50 mg of charcoal. There are at least three different methods for toluene using this sampling tube that utilize carbon disulfide (CS 2 ) as the desorption solvent. (Refs. 5.3-5.5)
In the work presented here, tests were done to validate procedures for charcoal tubes as well as Anasorb 747 tubes. Additional tests were done so the new method can also be used for determinations of peak and ceiling exposures to toluene. Also, the recommend sampling rate was reduced to 50 mL/min to allow samples to be taken for as long as 240 minutes, which makes it convenient to assess an all-day exposure to a worker by taking only two samples. The most significant change was in the solvent used to desorb the samples.
When air is drawn through activated charcoal tubes, a significant amount of water may be collected by adsorption along with the analytes of interest. (Ref. 5.6) The amount of water collected is dependent on the water content of the air and the volume of air sampled. Water is not very soluble in CS 2 , thus when samples containing excessive amounts of water are desorbed with this commonly used solvent, the desorbed water can form a separate layer. Only the CS 2 layer is analyzed by GC, so if an analyte of interest is appreciably soluble in water, it will partition into the aqueous layer and the concentration of the analyte may be grossly under determined. This problem does not occur for toluene because being fairly nonpolar, it is very soluble in CS 2 and only partially soluble in water. But toluene is frequently used with a mixture of solvents in workplaces, some of which may be very soluble in water. It is often desirable to analyze the mixture of solvents simultaneously from the same sample, so a solution to this problem was to use a desorption solvent that would result in a homogeneous solution that includes water after the samples are desorbed and one that would also desorb the analytes of interest with high efficiency.
A desorption solvent mixture consisting of 60/40 (v/v) N,N -dimethylformamide/carbon disulfide (DMF/CS 2 ) was successfully used in some recently validated SLTC methods for low molecular weight alcohols (Refs. 5.7-5.9) and was chosen for this present work. One milliliter of this solvent will assimilate up to 50 mg of water at room temperature and desorbs a wide variety of solvents with high efficiency.
It is imperative that an internal standard procedure be used in the analysis to compensate for the water that is desorbed and put into solution. For instance, if an external standard method is used and a sample that contains 45 mg of water is desorbed with 1.00 mL of 60/40 DMF/CS 2 , an uncorrectable error of approximately 4.5% is introduced. The amount of water (in this case 45 mg or 0.045 mL) that was adsorbed by the adsorbent is not determined in the analysis, so a correction for the dilution of the sample by the desorbed water can not be made. In this case, the final volume of the desorption solution is approximately 1.045 mL because of the desorbed water, not 1.00 mL. The necessary
conjugated with glycine in the liver to form hippuric acid. The hippuric acid is then excreted in the urine.
Repeated or prolonged skin exposure to toluene causes skin drying, fissuring, and dermatitis. Liquid splashed in the eyes of two workers caused transient corneal damage and conjunctival irritation with complete recovery within 48 hours.
Recent inhalation studies on rats exposed to levels of 600 to 1200 ppm and mice exposed to 120, 600, or 1200 ppm for two years found no evidence of carcinogenic activity.
1.1.3 Workplace exposure
Toluene is used in the manufacture of benzoic acid, benzaldehyde, explosives, dyes and many other organic compounds. It is also used as a solvent for paints, lacquers, gums, and resins and as a thinner for inks, perfumes, and dyes. It is used in the extraction of various principles from plants. It is a component in gasoline and is also used as a gasoline additive. (Ref. 5.13)
1.1.4 Physical properties (Ref. 5.13 unless otherwise noted)
CAS number: 108-88- molecular weight: 92. boiling point: 110.6°C melting point: –95°C appearance: colorless liquid density: 0.866 g/mL at 20°C molecular formula: C 7 H 8 vapor pressure: 2.92 kPa (21.9 mmHg) at 20°C (Ref. 5.14) flash point: 40 °F (4.4°C) (closed cup) odor: benzene-like explosive limits: 1.27-7% in air (Ref. 5.15) solubility: very slightly soluble in water [0.067% (w/w) in water at 23.5°C]; miscible with alcohol, chloroform, ether, acetone, glacial acetic acid, carbon disulfide. synonyms: methylbenzene; toluol; phenylmethane; Methacide. structural formula:
The analyte air concentrations throughout this method are based on the recommended sampling and analytical parameters. TWA target concentration samples are based on 240 minutes, ceiling samples on 10 minutes and peak samples on 1 minute of sampling/diffusive sampler exposure. Air concentrations listed in ppb and ppm are referenced to 25°C 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 2.60 pg. This is the amount of toluene that will give an instrument response that is significantly different from the background response of a reagent blank. (Sections 4.1 and 4.2)
1.2.2 Detection limit of the overall procedure
The detection limits of the overall procedure are 246 ng per sample (5.4 ppb or 20. μ g/m^3 ), 344 ng per sample (7.6 ppb or 28.7 μ g/m^3 ), 657 ng per sample (25 ppb or 93 μ g/m^3 ) and 904 ng per sample (67 ppb or 253 μ g/m^3 ) for charcoal tubes, Anasorb 747 tubes, 3M 3520 OVMs and SKC 575-002 samplers respectively. These are the amounts of toluene spiked on the respective samplers that will give instrument responses that are significantly different from the background responses of respective sampler blanks. (Sections 4.1 and 4.3)
1.2.3 Reliable quantitation limit
The reliable quantitation limits are 820 ng per sample (18.1 ppb or 68.3 μ g/m^3 ), 1146 ng per sample (25.4 ppb or 95.5 μ g/m^3 ), 2190 ng per sample (82 ppb or 309 μ g/m^3 ) and 3012 ng per sample (224 ppb or 844 μ g/m^3 ) for charcoal tubes, Anasorb 747 tubes, 3M 3520 OVMs and SKC 575-002 samplers respectively. These are the amounts of toluene spiked on the respective samplers that will give signals that are considered the lower limits for precise quantitative measurements. (Section 4.4)
1.2.4 Precision (analytical procedure)
The precisions of the analytical procedure, measured as the pooled relative standard deviations from standards over concentration ranges equivalent to 0.5 to 2 times the TWA target concentration, are 0.76%, 0.94% and 0.76% for the adsorbent tubes, 3M 3520 OVMs and SKC 575-002 samplers respectively. (Section 4.5)
1.2.5 Precision (overall procedure)
a) Adsorbent tubes samples
The precisions of the overall procedure at the 95% confidence level from the ambient temperature storage tests for TWA, ceiling and peak samples for charcoal tubes and Anasorb 747 tubes are given in Table 1.2.5.1. The TWA samples are 240-min samples taken from 200-ppm atmospheres, the ceiling samples are 10-min samples taken from 300-ppm atmospheres and the peak samples are 1-min samples taken from 500-ppm atmospheres. (Section 4.6)
Table 1.2.5. Precision of the Overall Procedure at the 95% Confidence Interval for Adsorbent Tubes Adsorbent TWA Samples Ceiling Samples Peak Samples Charcoal ±10.8% ±10.2% ±10.3%
Anasorb 747 ±10.1% ±10.1% ±10.5%
b) Diffusive samplers
The precisions of the overall procedure at the 95% confidence level from the ambient temperature storage tests for TWA and ceiling samples for 3M 3520 OVMs and SKC 575-002 samplers are given in Table 1.2.5.2. The TWA samples are 240-min samples taken from 200-ppm atmospheres and the ceiling samples are 10-min samples taken from 300-ppm atmospheres. There are different values given for each sampler for each of the levels, depending on whether the sampling site conditions are known. The possible cases would be when both, either, or neither temperature or atmospheric pressure are known. If the temperature is not known, the sampling site temperature is assumed to be 22.2±15°C (72±27°F) and a variability of ±7.7% is included. If the atmospheric pressure is not known, a variability ±3% is included. (Section 4.6)
plugs. The ends of the glass sampling tubes are heat sealed. Lot 120 charcoal and Lot 299 Anasorb 747 tubes were used for this evaluation.
2.1.2 Diffusive samplers
a) Samples are collected with either 3M (3M Occupational Health and Safety Products Division, St. Paul, MN) 3520 Organic Vapor Monitors (OVMs) or SKC 575-002 Passive Samplers (SKC, Inc., Fullerton, CA). The 3M 3520 OVMs are badges containing two activated charcoal disks. The secondary disk collects contaminant when the capacity of the primary disk has been exceeded. The SKC 575-002 Passive Samplers are badges that contain 500 mg of Anasorb 747 adsorbent. Lot 5163009 3M OVMs and Lot 263 SKC 575-002 Samplers were used in this evaluation.
b) A thermometer to determine the sampling site air temperature.
c) A barometer to determine the sampling site atmospheric pressure.
2.2 Reagents
None required
2.3 Technique
2.3.1 Adsorbent tubes
a) Immediately before sampling, break off the ends of the adsorbent tube. All tubes should be from the same lot.
b) Connect the sampling tube to the sampling pump with flexible, non-crimpable tubing. It is desirable to utilize a sampling tube holder that shields the employee from the sharp, jagged end of the sampling tube. Position the tube so that sampled air first passes through the larger adsorbent section.
c) Air being sampled should not pass through any hose or tubing before entering the sampling tube.
d) To avoid channeling, place the sampling tube vertically in the employee's breathing zone. Position the sampler so it does not impede work performance or safety.
e) After sampling for the appropriate time, immediately remove the sampling tube and seal it with plastic caps. Wrap each sample lengthwise with a Form OSHA-21 seal.
f) 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.
g) Record sample volumes (in liters of air), sampling times (minutes) and sampling rate (mL/min) for each sample on Form OSHA-91A.
h) Also list any compounds that could be considered potential interferences, especially solvents, that are being used in the sampling area.
i) Ship any bulk sample(s) in a container separate from the air samples.
2.3.2 3M OVMs (In general, follow the manufacturer’s instructions supplied with the samplers.)
a) The monitors 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 monitor. CAUTION- The monitor immediately begins to sample when the can is unsealed.
b) Keep the two closure caps with attached port plugs, cup and Teflon tubes in the can for later use. Close the can with the plastic lid.
c) Record the start time on the back of the monitor or on Form OSHA-91A.
d) Attach the monitor 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 monitor until the sampling period is terminated.
e) At the end of the sampling period, detach the monitor from the worker and remove the white film and retaining ring. Immediately snap a closure cap onto the primary (top) section of the monitor (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 5 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 monitor or on Form OSHA-91A.
f) The following steps should be performed in a low background area for a set of monitors as soon as possible after sampling.
g) Ready a blank by removing the white film and ring and attaching a closure cap onto an unused monitor.
h) For each monitor (one at a time), separate the primary (top) and secondary (bottom) sections of the monitor using the edge of a coin as a pry.
i) Securely snap a cup onto the bottom of the primary section.
j) Snap a closure cap onto the secondary section of the monitor and assure that the attached port plugs are placed firmly into the port holes.
k) Return the sampler sections with closure caps and cup in place to the metal can which contains the Teflon tubes (which will be used by the laboratory). Close the can with the plastic lid, and wrap it with a Form OSHA-21 seal.
l) Verify that the sampling times are properly recorded on Form OSHA-91A for each sample. Also identify blank samples on this form.
m) Record the room temperature and atmospheric pressure (station pressure) of the sampling site on Form OSHA-91A.
n) List any compounds that could be considered potential interferences, especially solvents, that are being used in the sampling area.
o) Submit the monitors (contained in the metal cans) to the laboratory for analysis as soon as possible.
p) Ship any bulk sample(s) in a container separate from the air samples.
2.3.3 SKC 575-002 Samplers (In general, follow the manufacturer’s instructions supplied with the samplers.)
2.4.2 Anasorb 747 tubes
The sampling capacity of the front section of Anasorb 747 sampling tubes was tested by sampling from a dynamically generated test atmosphere of toluene at 401.6 ppm ( mg/m^3 ). The samples were collected at a nominal flow rate of 50 mL/min and the relative humidity of the atmosphere was 73% at 29.1°C. The average 5% breakthrough volume was determined to be 20.6 L (31.1 mg or 412 min) from three determinations. (Section 4.9.2)
2.4.3 3M 3520 OVMs
The sampling rate and capacity of 3M 3520 OVMs were determined by taking samples from a dynamically generated test atmosphere of toluene (nominal concentration of 400 ppm or 1507 mg/m^3 ) for increasing time intervals. A sampling rate of 29.54 mL/min (at 760 mmHg, 25°C) and capacity of greater than 32 mg per sample (>21.2 L or >718 min) were obtained from this test. (Section 4.9.3)
2.4.4 SKC 575-002 Samplers
The sampling rate and capacity of SKC 575-002 Samplers were determined by taking samples from a dynamically generated test atmosphere of toluene (nominal concentration of 400 ppm or 1507 mg/m^3 ) for increasing time intervals. A sampling rate of 14.89 mL/min (at 760 mmHg, 25°C) and capacity of greater than 16 mg per sample (>10.6 L or > min) were obtained from this test. (Section 4.9.4)
2.5 Desorption efficiency
2.5.1 Charcoal tubes
a) The average desorption efficiency from charcoal tubes over the range of 0.5 to 2 times the TWA target concentration is 99.0%. (Section 4.10.1.a)
b) The desorption efficiency at 0.05, 0.1 and 0.2 times the target concentration was found to be 97.4, 98.2% and 98.4% respectively. (Section 4.10.1.a)
c) Desorbed samples remain stable for at least 24 h. (Section 4.10.1.b)
2.5.2 Anasorb 747 tubes
a) The average desorption efficiency from Anasorb 747 tubes over the range of 0.5 to 2 times the TWA target concentration is 99.1%. (Section 4.10.2.a)
b) The desorption efficiency at 0.05, 0.1 and 0.2 times the target concentration was found to be 97.3, 98.1% and 99.1% respectively. (Section 4.10.2.a)
c) Desorbed samples remain stable for at least 24 h. (Section 4.10.2.b)
2.5.3 3M OVMs
a) The average desorption efficiency from 3M OVMs over the range of 0.5 to 2 times the TWA target concentration is 98.1%. (Section 4.10.3.a)
b) The desorption efficiency at 0.05, 0.1 and 0.2 times the target concentration was found to be 98.4, 98.2% and 98.0% respectively. (Section 4.10.3.a)
c) Desorbed samples remain stable for at least 24 h. (Section 4.10.3.b)
2.5.4 SKC 575-002 Samplers
a) The average desorption efficiency from SKC 575-002 Samplers over the range of 0. to 2 times the TWA target concentration is 97.0%. (Section 4.10.4.a)
b) The desorption efficiency at 0.05, 0.1 and 0.2 times the target concentration was found to be 98.0, 98.1% and 97.6% respectively. (Section 4.10.4.a)
c) Desorbed samples remain stable for at least 24 h. (Section 4.10.4.b)
2.6 Recommended air volume and sampling rate
2.6.1 When using adsorbent tubes for TWA (long-term) samples, sample up to 12 L of air at 50 mL/min (up to 240 min). When using diffusive samplers, sample for as long as 240 minutes.
2.6.2 When using adsorbent tubes for ceiling samples, sample greater than 0.5 L of air at 50 mL/min (greater than 10 min). When using diffusive samplers, sample for greater than 10 minutes.
2.6.3 When using adsorbent tubes for peak samples, sample at least 0.05 L of air at 50 mL/min (at least 1 min). The use of diffusive samplers is not recommended for peak samples.
2.6.4 When short-term samples are collected, the air concentrations equivalent to the reliable quantitation limits becomes larger. For example, the reliable quantitation limits for charcoal tubes become 0.43 ppm (1.6 mg/m^3 ) for 10-min samples and 4.3 ppm (16 mg/m^3 ) for 1-min samples.
2.7 Interferences (sampling)
2.7.1 The presence of other contaminants in the sampled air can potentially reduce the capacity of all four samplers to collect toluene. Also, the sampling rates of diffusive samplers could possibly be altered. Interference studies were performed by sampling for 240 minutes from a test atmosphere (10% RH, 26°C, 654.8 mmHg) containing 396 ppm of toluene with 50 ppm of 2-butanone (MEK), 20 ppm of 4-methyl-2-pentanone (MIBK), 20 ppm of 1-butanol, 30 ppm of isobutyl acetate and 30 ppm of xylene. The presence of these compounds, which may represent typical substances that may be collected with toluene, did not have a significant effect on sample results using any of the samplers. (Section 4.11.1)
2.7.2 Short-term sampling interference studies were performed for all four samplers by sampling for 1 minute from a test atmosphere (10% RH, 25°C, 654.3 mmHg) containing 495 ppm of toluene with 50 ppm of 2-butanone (MEK), 20 ppm of 4-methyl-2-pentanone (MIBK), 20 ppm of 1-butanol, 30 ppm of isobutyl acetate and 30 ppm of xylene. The presence of these compounds, which may represent typical substances that may be collected with toluene, did not have a significant effect on sample results using any of the samplers.(Section 4.11.2)
2.7.3 A reverse diffusion study for the diffusive samplers and a stripping study for the adsorbent tubes was performed by sampling a 402 ppm atmosphere of toluene (78% RH, 23.5°C, 649.2 mmHg) for 120 minutes with six of each samplers. Three samplers from each set were additionally subjected to 120 minutes of the same atmosphere without the toluene present to determine if any of the collected toluene diffused off of the diffusive samplers and also whether it was stripped off of the adsorbent tubes. Upon analysis of the samples, the average recovery of the removed samplers versus the average recovery of the samplers that were additionally exposed to the atmosphere without toluene was within 90% for all samplers, indicating that reverse diffusion and stripping are not significant. (Section 4.11.3)
2.7.4 The effects of sampling from relatively dry atmospheres was investigated by sampling from a 403.2-ppm toluene atmosphere (9% RH, 25.3°C, 654.5 mmHg) for 240 minutes and by
3.2.5 The desorption solvent consists of 60/40 (v/v) DMF/CS 2 containing 1.0 milliliter of internal standard per liter of solution (1 μ L/mL).
3.2.6 GC grade nitrogen, air and hydrogen.
3.3 Standard preparation
3.3.1 Prepare standards by injecting microliter amounts of toluene into vials containing 1.0 mL (for adsorbent tubes) or 2.0 mL (for diffusive samplers) of desorption solvent delivered from the same dispenser used to desorb samples. For example, inject 6.00 μ L of toluene into a vial containing 1.0 mL of desorption solvent. Assuming the density of toluene is 0. g/mL (which is dependent on the temperature of the toluene), this standard contains 5196 μ g of toluene per sample for adsorbent tube samples.
3.3.2 Bracket sample concentrations with standard concentrations. If upon analysis, sample concentrations fall outside the range of prepared standards, prepare and analyze additional standards to ascertain the linearity of instrument response or dilute high samples with desorption solvent and reanalyze the diluted samples.
3.4 Sample preparation
3.4.1 Adsorbent tube samples
a) Transfer each section of adsorbent from the sampling tubes to separate labeled vials. Discard the glass tubes, urethane foam plugs and glass wool plugs.
b) Add 1.0 mL of desorption solvent to each vial using the same dispenser as used for preparation of standards.
c) Immediately cap the vials.
d) Allow the adsorbent sections to desorb for 30 minutes. Periodically apply gentle agitation to the vials during the desorption period.
3.4.2 3M 3520 OVMs (In general, follow the manufacturer’s instructions supplied with the samplers.)
a) Remove each sampler section from its individual metal can, along with the sections of Teflon®^ tubing. Assure that the closure caps are firmly snapped to the primary and secondary sections of all the samplers. Also assure that all cap plugs are firmly seated in the cap ports. Any deviations must be noted.
b) Prepare one section of sampler at time by temporarily removing the cap plugs from the ports and adding 2.0 mL of desorption solvent through the center port. This is most easily done by dispensing two 1.0-mL aliquots of desorption solvent using a dispenser. Immediately replace the plugs in the ports.
c) Allow the sampler sections to desorb for 30 minutes. Periodically apply gentle agitation to the sampler sections during the desorption period.
d) Transfer the solution from each sampler section by removing both plugs from the ports, inserting a decanting spout (a small section of Teflon tubing) into the rim port and pouring the liquid through the spout into a labeled autosampler vial. Immediately cap each vial.
3.4.3 SKC 575-002 Samplers (In general, follow the manufacturer’s instructions supplied with the samplers.)
a) Cut off the ends of the two protruding tubes of each sampler with a razor blade or sharp knife.
b) Slowly add 1.0 mL of desorption solvent through one of the protruding tubes (ports). After about 30 seconds, slowly add another 1.0 mL of desorption solvent.
c) Immediately insert plugs into the ports.
d) Mount the samplers in the sampler rack (SKC Cat. No. 226-04-5) of a specialized shaker (SKC Cat. No. 226D-03-1) and shake the samplers for 1 hour.
e) According to the manufacturer of the sampler, do not leave the desorbed sample in the sampler. Transfer each desorbed sample by removing the plugs from the sampler ports, firmly inserting the tapered end of a supplied Teflon tube into the outer port and carefully pouring the solution through the Teflon tube into a labeled autosampler vial.
3.5 Analysis
3.5.1 GC conditions
zone temperatures: column- 60 °C (isothermal) injector- 250 °C detector- 275 °C gas flows: hydrogen (carrier)- 2.5 mL/min (43 kPa head pressure) nitrogen (makeup)- 50 mL/min hydrogen (flame)- 38 mL/min air- 450 mL/min signal range: 0 injection volume: 1.0 μ L (with a 100:1 split) column: 30-m × 0.32-mm i.d. fused silica, XTI-5 1.0- μ m df retention times: toluene- 5.2 min ethylbenzene- 9.8 min (internal standard) (CS 2 - 1.7 min, DMF- 6.1 min)
Figure 3.5.1.1. Chromatogram of a standard near the TWA target concentration for the adsorbent tubes. Key: (1) CS 2 , (2) toluene, (3) DMF, (4) ethylbenzene.
Figure 3.5.1.2. Chromatogram of a standard near the TWA target concentration for 3M 3520 OVMs. Key: (1) CS 2 , (2) toluene, (3) DMF, (4) ethylbenzene.
Figure 3.5.1.7. Chromatogram of a standard near the peak target concentration for the adsorbent tubes. Key: (1) CS 2 , (2) toluene, (3) DMF, (4) ethylbenzene.
3.5.2 Peak areas are measured by an integrator or other suitable means.
3.5.3 An internal standard (ISTD) calibration method is used. A calibration curve is prepared by analyzing standards and plotting micrograms of toluene per sample versus ISTD-corrected area counts of the toluene peaks. Sample concentrations must be bracketed by standards.
Figure 3.5.3.1. Calibration curve for adsorbent tubes constructed from the data in Table 4.5. The equation of the line is Y = 150.7X-15400.
Figure 3.5.3.2. Calibration curve for 3M 3520 OVMs constructed from the data in Table 4.5.2. The equation of the line is Y = 74.93X+1609.
Figure 3.5.3.3. Calibration curve for SKC 575- samplers constructed from the data in Table 4.5.3. The equation of the line is Y = 75.57X-549.7.
3.6 Interferences (analytical)
3.6.1 Any compound that produces a response on a flame ionization detector and has the same general retention time of toluene or the internal standard is a potential interference. Possible interferences should be reported to the laboratory with submitted samples by the industrial hygienist. These interferences 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 The desorption efficiency from wet samplers was investigated by spiking samplers with amounts of toluene equivalent to the mass that would be collected for 240 minutes from atmospheres containing 200 ppm. Before being spiked with toluene, humid air (~80% RH, 25 °C) had been drawn through the adsorbent tubes at 50 mL/min for 240 minutes. Similarly, the diffusive samplers had been exposed to the humid atmosphere for 240 minutes. The desorption efficiencies were comparable to those reported in Section 2.5. (Section 4.12)
3.6.4 When necessary, the identity or purity of an analyte peak may be confirmed with additional analytical data. (Section 4.13)
3.7 Calculations
3.7.1 Adsorbent tube samples
The toluene concentration for samples is obtained from the appropriate calibration curve in terms of micrograms of toluene per sample, uncorrected for desorption efficiency. The air concentration is calculated using the following formulae. The back (50-mg) section is analyzed primarily to determine if there was any breakthrough from the front 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 on the blank.
mg/m³ = ( μ g of toluene per sample)/((L of air sampled)(desorption efficiency))
where: desorption efficiency = 0.990 for Charcoal and 0.991 for Anasorb 747 Tubes L of air sampled = [(sampling time, min)(sampling rate, mL/min)]/
ppm = (mg/m³)(24.46)/(molecular weight of analyte) = (mg/m³)(0.2655)
where: 24.46 is the molar volume at 25°C and 101.3 kPa (760 mmHg) and the molecular weight of toluene = 92.
3.7.2 3M 3520 OVMs and SKC 575-002 Samplers
The toluene concentration for samples is obtained from the appropriate calibration curve in terms of micrograms of toluene per sample, uncorrected for desorption efficiency. The air concentration is calculated using the following formulae. For the 3M OVMs, the back section is analyzed primarily to determine if there was any breakthrough from the front 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, the amount found is multiplied by 2.2 (as per manufacturer’s instructions) and then added to the amount found on the corresponding front section. This total amount is then corrected by subtracting the total amount (if any) found on the blank.
- Backup Data
4.1 Determination of detection limits
Detection limits (DL), in general, are defined as the amount (or concentration) of analyte that gives an instrument response (YDL) that is significantly different (three standard deviations (SDBR)) from the background response (YBR).
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 analytical standards or 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 equation. The following calculations derive a formula for DL:
Yobs = observed response Yest = estimated response from regression curve n = total no. of data points k = 2 for a linear regression curve
At point YDL on the regression curve
A = analytical sensitivity (slope)
therefore
Substituting 3(SEE) + YBR for YDL gives
4.2 Detection limit of the analytical procedure (DLAP)
The DLAP is measured as the mass of analyte introduced into the chromatographic column. Ten analytical standards were prepared in equal descending increments with the highest standard containing 4325 ng of toluene per mL. This standard produces a peak approximately 10 times the baseline noise of a reagent blank when a 1- μ L injection with a 1:100 split is made onto the GC column. Standards, plus a reagent blank, were analyzed and the data obtained were used to determine the required parameters (A and SEE) for the calculation of the DLAP. Values of 17. and 15.3 were obtained for A and SEE respectively. The DLAP was calculated to be 2.60 pg.
Table 4. DLAP for Toluene concentration mass on column peak area (ng/mL) (pg) ( μ V•s) 0.000 0.00 0 432.5 4.325 92. 865.0 8.650 167 1298 12.98 226 1730 17.30 338 2162 21.62 368 2595 25.95 456 3028 30.28 547 3460 34.60 641 3892 38.92 696 4325 43.25 761
Figure 4.2. Plot of data from Table 4.2 to determine the DLAP. The equation of the line is Y = 17.66X + 8.40.
4.3 Detection limit of the overall procedure (DLOP)
The DLOP is measured as mass per sample and expressed as equivalent air concentrations, based on the recommended sampling parameters. Ten samplers of each type were spiked with equal descending increments of toluene such that the highest sampler loadings were 4325 ng/sample for the adsorbent tubes and 8650 ng/sample for the 3M 3520 OVMs and SKC samplers. (The diffusive samplers were spiked with twice the amounts of toluene compared to adsorbent tubes because they are desorbed with 2 mL of solvent versus 1 mL for the adsorbent tubes.) These are the amounts, when spiked on the samplers, that would produce peaks approximately 10 times the baseline noise for sample blanks. These spiked samplers, plus blanks, 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 DLOPs. Values of 0.1768 and 14.5, 0.1745 and 20.0, 0.0831 and 18.2, and 0.0943 and 28.4 were obtained for A and SEE for charcoal tubes, Anasorb 747 tubes, 3M 3520 OVMs and SKC 575-002 samplers respectively. The DLOPs were calculated to be 246 ng per sample (5.4 ppb or 20.5 μ g/m^3 ), 344 ng per sample (7.6 ppb or 28.7 μ g/m^3 ), 657 ng per sample (25 ppb or 93 μ g/m^3 ) and 904 ng per sample (67 ppb or 253 μ g/m^3 ) for charcoal tubes, Anasorb 747 tubes, 3M 3520 OVMs and SKC 575-002 samplers respectively.
Table 4.3. Detection Limit of the Overall Procedure for Charcoal Tubes mass (ng) per peak area sample ( μ V•s) 0.0 0 432.5 90. 865.0 162 1298 244 1730 322 2162 386 2595 491 3028 518 3460 639 3892 686 4325 776 Figure 4.3.1. Plot of data from Table 4.3.1 to determine the DLOP/RQL for charcoal tubes. The equation of the line is Y = 0.1768X + 9.83.
