Methods Development Team
Industrial Hygiene Chemistry Division
OSHA Salt Lake Technical Center
Sandy UT 84070

1. General Discussion
   1. Background
      1. History

         Xylenes is a collective term for a mixture of m-, o-, and p- isomers of xylene. These isomers differ only in placement of two methyl groups on a benzene ring. Technical and commercial grades of xylenes often contain substantial amounts of ethylbenzene (10-50%), and perhaps minor amounts of other solvents as well. Mixtures of xylenes and ethylbenzene are occasionally termed mixed xylenes.^{1, 2}

         Most occupational exposure to xylenes also results in exposure to ethylbenzene because technical and commercial grades of xylenes are often used by industry. Therefore, test atmospheres used in this work were prepared with a commercial source of xylenes to simulate workplace environment. This source of xylenes contained 43% m-xylene, 20% o-xylene, 19% p-xylene, and 15% ethylbenzene. Xylenes target concentration in test atmospheres were approximately 100 ppm for the sum of the three isomers. These xylenes air concentrations resulted in approximately 17 ppm ethylbenzene because of its level in the commercial xylenes. Xylenes and ethylbenzene can be present in the workplace in any combination and level, and this method should be satisfactory to monitor exposures to xylenes, individual xylene isomers, and ethylbenzene. The method recommends charcoal tubes for active sampling, and SKC 575-002 Passive Samplers for diffusive sampling. Samples are extracted with carbon disulfide, and are analyzed by GC using a flame ionization detector.

         Determination of xylenes is well documented in the literature^{3, 4}, and one may question why this work was necessary. SLTC has begun to develop sampling and analytical methods which permit the use of diffusive, as well as, active sampling. One criterion for selection of chemicals for this evaluation program is the number of sample requests. Analysis of xylenes is one of the most requested solvent determinations performed at SLTC.

      2. Toxic effects (This section is for information only and should not be taken as the basis of OSHA policy.)

         Xylenes

         There is no appreciable difference in the toxicological effects of the individual xylene isomers and those of mixed isomers. Xylenes are eye, skin, and mucous membrane irritants. They can cause narcosis at high levels. Xylenes can cause liver and kidney damage. There is little (if any) evidence for the carcinogenicity of xylenes in experimental animals. The ACGIH TLV-TWA was set at 100 ppm, and the STEL at 150 ppm, for mixed xylene isomers and for individual isomers. It was anticipated that irritant effects would be minimal, and that neither narcosis nor chronic injury would result from exposures at these levels.⁵

         Ethylbenzene

         Ethylbenzene is a skin and mucous membrane irritant. It has acute and possibly chronic central nervous system effects that include vertigo, unconsciousness, tremors, and changes in respiration. Animal experiments suggest that ethylbenzene causes damage to the liver, kidneys, and testes. It was the opinion of the ACGIH TLV Committee that no systemic effects would be expected at concentrations which produce skin and eye irritation. The ACGIH TLV-TWA was set at 100 ppm and the STEL at 125 ppm to prevent such irritation.⁶ ACGIH published in the 1998 TLVs and BEIs booklet⁷ a "Notice of Intended Changes" to add the A3 notation to ethylbenzene. A3 is defined as "Confirmed Animal Carcinogen with Unknown Relevance to Humans".

      3. Workplace exposure

         The main source of mixed xylenes since World War II has been reformed petroleum fractions. Earlier, xylenes were produced from coal. Coal may again become an important source as the large coal reserves in the United States are developed for petrochemical uses.⁸ U.S. production of xylenes in 1995 was 9.4 billion pounds, and that for ethylbenzene was 13.7 billion pounds.⁹

         Most mixed xylenes are used to blend gasoline. Mixed xylenes are also used in the paint and coatings industry. m-Xylene is used to produce isophthalic acid, which is used in polyesters; o-xylene is used to produce phthalic anhyride, which is used in plasticizers; p-xylene is used to produce terephthalic acid and dimethyl terephtalate, both of which are used to produce polyesters. o-Xylene and p-xylene are used in vitamin and pharmaceutical synthesis, and to produce insecticides. Ethylbenzene is used to produce styrene.^{10, 11}

      4. Physical properties (¹² unless otherwise noted)

         	xylenes	m-xylene	o-xylene	p-xylene	ethylbenzene
         CAS number13	1330-20-714	108-38-3	95-47-6	106-42-3	100-41-4
         IMIS number15	2590				1080
         molecular weight16	106.17	106.17	106.17	106.17	106.17
         boiling point (°C)	137-145	138.8	144	138.5	136.19
         melting point (°C)		-47.4	-25	13.2	-95.0117
         density (°C)	about 0.86	0.868 (15)	0.880 (20/4)	0.861 (20)	0.867 (20)
         molecular formula	C8H10	C8H10	C8H10	C8H10	C8H10
         flash point (°F)	81-115	85	115	81	59
         vapor pressure     (kPa, (°C))18, 19		1.1 (25)	0.9 (25)	1.2 (25)	0.9 (20)

         Xylenes (dimethylbenzene, xylol) are soluble in alcohol and ether, but insoluble in water. Each of the mixed xylenes is a clear, colorless liquid at room temperature, however, p-xylene forms crystals at a relatively high temperature. The xylene isomers: m-xylene (1,3-dimethylbenzene), o-xylene (1,2-dimethylbenzene), and p-xylene (1,4-dimethylbenzene) are soluble in alcohol and ether; but they are insoluble in water. Ethylbenzene (phenylethane) is soluble in alcohol, benzene, carbon tetrachloride, and ether; it is but almost insoluble in water.²⁰

         Structural formulas:

         

         Structural formula of m-xylne

         

         Structural formula of o-xylne

         

         Structural formula of p-xylne

         

         Structural formula of ethyl benzene

         This method was evaluated according to OSHA SLTC "Evaluation Guidelines for Air Sampling Methods Utilizing Chromatographic Analysis²¹. The Guidelines define analytical parameters and specify required laboratory tests, statistical calculations and acceptance criteria. The analyte concentrations throughout this method are based on the recommended sampling and analytical parameters. Air concentrations in ppm and ppb are referenced to 25 °C and 101.3 kPa (760 mmHg).

   2. Limit defining parameters
      1. Detection limit of the analytical procedure

         Table 1.2.1
         DLAP (pg per sample)

         xylenes	m-xylene	o-xylene	p-xylene	ethylbenzene
         14.5	2.1	8.4	14.0	5.7

         The detection limits of the analytical procedure (DLAP) are shown in Table 1.2.1. These are the amounts of analyte that will give detector responses significantly different from the response of a reagent blank. (Section 4.1)

      
      
      
      2. Detection limit of the overall procedure

         Table 1.2.2.1
         DLOP for Charcoal Tubes

         analyte	ng	ppb	µg/m3
         xylenes m-xylene o-xylene p-xylene ethylbenzene	322 159 239 100 129	6.2 3.0 4.6 1.9 2.5	26.8 13.2 19.9 8.3 10.8

         Charcoal tubes

         The detection limits of the overall procedure (DLOP) are shown in Table 1.2.2.1. These are the amounts of analyte spiked on the samplers that will give detector responses significantly different from the response of a sampler blank. (Section 4.2)

          

          

          

         SKC 575-002 Passive Samplers

         Table 1.2.2.2
         DLOP for SKC 575-002
         Passive Samplers

         analyte	ng	ppb	µg/m3
         xylenes m-xylene o-xylene p-xylene ethylbenzene	847 448 325 437 315	58.2 31.1 21.9 30.1 21.9	252.8 134.9 95.0 130.8 94.9

         The detection limits of the overall procedure (DLOP) are shown in Table 1.2.2.2. These are the amounts of analyte spiked on the samplers that will give detector responses significantly different from the response of a sampler blank. (Section 4.2)

      
      
      
      
      
      
      
      
      
      3. Reliable quantitation limit

         Table 1.2.3.1
         RQL for Charcoal Tubes

         analyte	ng	ppb	µg/m3
         xylenes m-xylene o-xylene p-xylene ethylbenzene	1072 531 795 334 431	20.6 10.2 15.3 6.4 8.3	89.3 44.2 66.2 27.8 35.9

         Charcoal tubes

         The reliable quantitation limits (RQL) are shown in Table 1.2.3.1. These are the amounts of analyte that will give detector responses that are considered the lower limits for precise quantitative measurements. (Section 4.2)

          

          

          

         SKC 575-002 Passive Samplers

         Table 1.2.3.2
         RQL for SKC 575-002 Passive Samplers

         analyte	ng	ppb	µg/m3
         xylenes m-xylene o-xylene p-xylene ethylbenzene	2823 1495 1084 1456 1049	194.1 103.7 73.0 100.4 72.8	842.7 450.3 317.0 435.9 316.0

         The reliable quantitation limits (RQL) are shown in Table 1.2.3.2. These are the amounts of analyte that will give detector responses that are considered the lower limits for precise quantitative measurements. (Section 4.2)

      
      
      
      
      
      
      
      
      
      
      4. Instrument calibration

         Table 1.2.4
         Coefficients of Determination (r²)
         and Nondetermination (k²)

         analyte	charcoal tubes		SKC 575-002 Pass Samplers
         	r2	k2	r2	k2
         m-xylene	0.9994	6×10-4	0.9998	2×10-4
         o-xylene	0.9995	5×10-4	0.9998	2×10-4
         p-xylene	0.9994	6×10-4	0.9998	2×10-4
         ethylbenzene	0.9994	6×10-4	0.9998	2×10-4

         The coefficients of determination (r²) and of nondetermination (k²) for the calibration curves are shown in Table 1.2.4. The calibrated range was 0.5 to 2 times the OSHA PEL. (Section 4.3)

      
      
      
      
      
      
      
      
      
      
      
      
      5. Precision (overall procedure)

         Table 1.2.5.1
         Precision of the Overall Procedure for Charcoal Tubes

         analyte	precision (±%)
         xylenes m-xylene o-xylene p-xylene ethylbenzene	10.8 10.7 11.0 11.1 10.6

         Charcoal tubes

         The precision of the overall procedure at the 95% confidence interval for the ambient temperature 16-day storage test (at the target concentration) are shown in Table 1.2.5.1. Each precision includes an additional 5% for sampling pump variability. (Section 4.4)

         SKC 575-002 Passive Samplers

         The precision of the overall procedure at the 95% confidence interval for the ambient temperature 16-day storage tests (at the target concentration) are given in Table 1.2.5.2. They each include an additional 8.7% for sampling rate variability. There are different values given, depending on whether both, either, or neither temperature or atmospheric pressure are known at the sampling site. If the sampling-site temperature (T) is unknown, it is assumed to be 22.2 ± 15 °C (72 ± 27 °F) and a variability of ±7.7% is included. If the atmospheric pressure (P) is unknown, it is estimated from sampling-site elevation and a variability of ±3% is included. (Section 4.4)

         Table 1.2.5.2
         Precision of the Overall Procedure for SKC 575-002 Passive Samplers (±%)

         condition	xylenes	m-xylene	o-xylene	p-xylene	ethylbenzene
         both T and P known only T known only P known neither T nor P known	18.2 19.1 23.7 24.4	18.3 19.2 23.7 24.4	18.1 19.0 23.6 24.3	18.3 19.2 23.7 24.4	18.4 19.3 23.8 24.5

      6. Recovery

         Table 1.2.6
         Recovery (%)

         analyte	charcoal tubes	SKC 575-002 Passive Samlers
         xylenes m-xylene o-xylene p-xylene ethylbenzene	99.1 99.6 98.5 98.5 100.2	97.7 98.2 96.6 97.8 99.5

         The recoveries from samples used in 16-day ambient temperature storage tests remained above those shown in Table 1.2.6. (Section 4.5)

      7. Reproducibility

         Twelve samples (six active and six diffusive) collected from test atmospheres were submitted for analysis by SLTC. The samples were analyzed according to instructions presented in a draft copy of this method after 16 and 22 days of storage at ambient temperature for the active and diffusive samplers, respectively. No individual result deviated from its theoretical value by more than the precision reported in Section 1.2.5. (Section 4.6)

2. Sampling procedure

   All safety practices that apply to the work area being sampled should be followed. The sampling equipment should be attached to the worker in such a manner that it will not interfere with work performance or safety.

   1. Apparatus
      1. Charcoal tubes

         Samples are collected with a personal sampling pump calibrated, with the sampler attached, to within ±5% at 50 mL/min.

         Samples are collected with 7-cm × 4-mm i.d. × 6-mm o.d. flame sealed glass sampling tubes containing two sections of coconut shell charcoal. The front section contains 100 mg and the back section contains 50 mg of charcoal. The sections are held in place and separated with glass wool and polyurethane plugs. Commercially prepared sampling tubes were purchased from SKC for this evaluation (SKC Catalog no. 226-01, Lot 2000).

      2. SKC 575-002 Passive Samplers

         Samples are collected with SKC 575-002 Passive Samplers. These samplers contain 500 mg of Anasorb 747. Lot numbers 347, 764, and 872 were used in this evaluation.

         A thermometer and a barometer are needed to determine sampling site temperature and pressure.

   2. Reagents

      None required.

   3. Technique
      1. Charcoal tubes

         Immediately before sampling, break off both ends of the flame sealed sampling tube to provide openings approximately half the internal diameter of the tube. Wear eye protection when breaking tubes. Use sampling tube holders to shield the employee from the sharp, jagged ends of the sampling tubes. All sampling tubes should be from the same lot.

         Use the smaller charcoal section of the sampling tube as a back-up and position it nearest the sampling pump. Attach the sampling tube to the sampling pump so that the tube is in an approximately vertical position with the inlet down during sampling. Position the sampling tube so that it does not impede work performance or safety.

         Draw air to be sampled directly into the tube inlet. Sampled air is not to pass through any hose or tubing before entering the sampling tube.

         Remove the sampler and seal the tube with plastic end caps after sampling for the appropriate time. Seal each sample end-to-end with an OSHA-21 form as soon as possible.

         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.

         Record sample air volume in liters for each sample, and record any potential interference.

         Submit the samples to the laboratory for analysis as soon as possible after sampling. Store the samples at reduced temperature if delay is unavoidable. Ship any bulk samples separate from air samples.

      2. SKC 575-002 Passive Samplers (In general, follow the manufacturer's instructions)

         Remove the sampler from the clear package just before sampling. CAUTION - The monitor begins to sample as soon as it is removed from this package. Retain the O-ring, press-on cover, cover retainer, port plugs, and PTFE tube for later use.

         Record the start time on the sampler label, or on the Form OSHA-91A.

         Attach the sampler near the worker's breathing zone with the perforations in the sampler facing out. Assure that the area directly in front of the sampler is unobstructed throughout the sampling period.

         Remove the sampler from the worker immediately at the end of the sampling period. Attach the cover with the O-ring in place onto the sampler using the cover retainer. Inspect the O-ring to be sure it is forming a good seal around the entire circumference of the sampler. Record the stop time on the sampler label, or on the Form OSHA-91A.

         Prepare a blank sample by removing it from its clear package, and then immediately attaching a cover with the O-ring in place onto it.

         Seal each sample with an OSHA-21 form.

         Verify that sampling times are properly recorded on Form OSHA-91A for each sample. Identify blank samples on this form.

         Record sampling site temperature and atmospheric pressure (station pressure) on Form OSHA-91A.

         List any chemicals that could be considered potential interferences, especially solvents, that are in use in the sampling area.

         Submit the samples to the laboratory for analysis as soon as possible. Store the samples in a refrigerator if delay is unavoidable. Include the port plugs and PTFE tubes which will be used in the laboratory analysis.

         Ship any bulk samples separate from air samples.

   4. Sampler capacity
      1. Charcoal tubes

         The sampling capacity of SKC Lot 2000 charcoal tubes was tested by sampling from a dynamically generated test atmosphere of mixed xylenes (1027 mg/m³ or 237 ppm). Samples were collected at 50 mL/min and the relative humidity was about 78% at 21 °C. No breakthrough from the front to the back section was observed, even after sampling for ten hours. The 5% breakthrough sampling time was determined to be in excess of 600 min. (Section 4.7.1)

      2. SKC 575-002 Passive Samplers

         The sampling rate and capacity of SKC 575-002 Passive Samplers were determined by sampling from dynamically generated test atmospheres of mixed xylenes (1027 mg/m³ or 237 ppm, at 78% relative humidity and 21 °C) for increasing time intervals. Sampling rates of 13.82 mL/min for m-xylene, 14.24 mL/min for o-xylene, 13.94 mL/min for p-xylene, and 13.83 mL/min for ethylbenzene at 760 mmHg and 25 °C were obtained from these tests. Sampler capacity was never exceeded, even after sampling for ten hours. (Section 4.7.2)

   5. Extraction efficiency

      It is the responsibility of the analytical laboratory to occasionally determine or confirm extraction efficiency because the adsorbent material, reagents, or technique may be different from those presented in this method.

      1. Charcoal tubes

         Mean extraction efficiencies (EE) of the analytes from SKC Lot 2000 charcoal are presented in Table 2.5.1. The range studied was from the RQL to 2 times the 100 ppm OSHA PEL for each xylene isomer, and for ethylbenzene. The extraction efficiency was not affected by the presence of water. (Section 4.8.1)

         Table 2.5.1
         Extraction Efficiency from Charcoal (%)

         m-xylene	o-xylene	p-xylene	ethylbenzene
         96.3	93.8	96.1	97.2

      2. SKC 575-002 Passive Samplers

         Mean extraction efficiencies (EE) of the analytes from SKC Anasorb 747 (the adsorbent in SKC 575-002 Passive Samplers) are presented in Table 2.5.2. The range studied was from the RQL to 2 times the 100 ppm OSHA PEL for each xylene isomer, and for ethylbenzene. The extraction efficiency was not affected by the presence of water. (Section 4.8.2)

         Table 2.5.2
         Extraction Efficiency form Anasorb 747 (%)

         m-xylene	o-xylene	p-xylene	ethylbenzene
         96.1	89.4	95.3	99.1

   6. Recommended sampling time and sampling rate
      1. Charcoal tubes

         Sample for up to 4 hours at 50 mL/min when using SKC 226-01 charcoal tubes to collect long-term samples. Sample for more than 5 min at 50 mL/min to collect short-term samples.

      2. SKC 575-002 Passive Samplers

         Table 2.6.2
         Sampling Rates for SKC 575-002 Passive
         Samplers (mL/min) at 760 mmHg and 25 °C

         m-xylene	o-xylene	p-xylene	ethylbenzene
         13.82	14.24	13.94	13.83

         Sample for up to 4 hours when using SKC 575-002 Passive Samplers to collect long-term samples. Sample for more than 5 min to collect short-term samples.

      3. The air concentration equivalent to the reliable quantitation limit becomes larger when short-term samples are collected. For example, the reliable quantitation limit for xylenes is 733 ppb (3180 µg/m³) when 0.25 L of air is sampled using charcoal tubes.
   7. Sampling interferences (Section 4.9)
      1. Charcoal tubes

         Retention

         The ability of the sampler to retain the analytes following collection was tested. The retention efficiency of all analytes for all samples was above 100.8% when three charcoal tubes containing 3 mg of mixed xylenes were used to sample 9 L of contaminant-free air having a relative humidity of 80% at 20 °C.

         Low relative humidity

         The ability of the sampler to collect and retain the analytes at low relative humidity was tested. The collection efficiency of all analytes for all samples was above 99.2% when three charcoal tubes were used to sample 12 L of air containing two times the target concentration of mixed xylenes and having a relative humidity of 5% at 20 °C.

         Low concentration

         The ability of the sampler to collect and retain the analytes at low concentration was tested. The collection efficiency of all analytes for all samples was above 94.6% when three charcoal tubes were used to sample 12 L of air containing 0.1 times the target concentration of mixed xylenes and having a relative humidity of 80% at 22 °C.

         Interference

         The ability of the sampler to collect and retain the analytes in the presence of potential sampling interferences was tested. The collection efficiency of all analytes for all samples was above 101.2% when three charcoal tubes were used to sample 12 L of air containing one times the target concentration of mixed xylenes, 365 mg/m³ toluene, 372 mg/m³ butyl acetate, and a relative humidity of 81% at 21 °C.

      2. SKC 575-002 Passive Samplers

         Reverse diffusion

         The sampling method was tested for reverse diffusion. The retention efficiency of all analytes for all samples was above 99.6% when three SKC 575-002 Passive Samplers containing 0.9 mg of mixed xylenes were used to sample contaminant-free air having a relative humidity of 80% at 20 °C for three hours.

         Low relative humidity

         The sampling method was tested to determine if the sampling rates remained constant at low relative humidity. The sampling rate of all analytes for all samples was above 97.8% of the sampling rate reported in Section 2.6.2 when three SKC 575-002 Passive Samplers were used to sample air containing two times the target concentration of mixed xylenes and having a relative humidity of 5% at 20 °C for four hours. Low humidity did not affect the sampling rates.

         Low concentration

         The sampling method was tested to determine if the sampling rates remained constant at low concentration. The sampling rate of all analytes for all samples was above 95.0% of the sampling rate reported in Section 2.6.2 when three SKC 575-002 Passive Samplers were used to sample air containing 0.1 times the target concentration of mixed xylenes and having a relative humidity of 80% at 22 °C for four hours.

         Interference

         The sampling method was tested to determine if the sampling rates remained constant in the presence of sampling interferences. The sampling rate for all analytes for all samples was above 94.3% of the sampling rate reported in Section 2.6.2 when three SKC 575-002 Passive Samplers were used to sample air containing one times the target concentration of mixed xylenes, 365 mg/m³ toluene, 372 mg/m³ butyl acetate, and a relative humidity of 81% at 21 °C for four hours.

3. Analytical procedure

   Adhere to the rules set down in your Chemical Hygiene Plan (which is mandated by the OSHA Laboratory Standard). Avoid skin contact and inhalation of all chemicals.

   1. Apparatus
      1. A GC equipped with a flame ionization (FID) detector. A Hewlett-Packard Model 5890 Series II GC equipped with a ChemStation, an automatic sample injector, and an FID were used in this evaluation.
      2. A GC column capable of separating mixed xylenes from the extraction solvent, internal standards, and potential interferences. A J&W Scientific 60-m × 0.32-mm i.d. DB-Wax (0.5 µm df) capillary column was used in this evaluation.
      3. An electronic integrator or other suitable means of measuring GC detector response. A Waters Millennium Chromatography Manager system was used in this evaluation.
      4. Two and four-milliliter glass vials with PTFE-lined septum caps.
      5. One and two-milliliter volumetric pipets.
      6. A SKC Desorption Shaker with rack (226D-03K) was used to extract SKC 575-002 Passive Samplers in this evaluation.
   2. Reagents
      1. Xylenes, Isomers plus ethylbenzene, 98.5+%, A.C.S. reagent, Aldrich Chemical Co., Lot TR 02505LR, was used in this evaluation.
      2. m-xylene, 99+%, anhydrous, Aldrich Chemical Co., Lot 00249MQ, was used in this evaluation.
      3. o-Xylene, 98%, Spectrophotometric Grade, Aldrich Chemical Co., Lot 07946PN, was used in this evaluation.
      4. p-Xylene, 99+%, anhydrous, Aldrich Chemical Co., Lot TQ 25949MQ, was used in this evaluation.
      5. Ethylbenzene, 99.8%, anhydrous, Aldrich Chemical Co., Lot DR 03249JQ, was used in this evaluation.
      6. Carbon disulfide (CS₂), 99.9+%, low benzene content, Aldrich Chemical Co., Lot 07546PN, was used in this evaluation.
      7. 1-Phenylhexane (hexylbenzene), 97%, Aldrich Chemical Co., Lot 03006PZ, was used as an internal standard for SKC 575-002 Passive Samplers in this evaluation.
      8. p-Cymene, 99%, Aldrich Chemical Co., Lot 11703TR, was used as an internal standard for charcoal tube samples in this evaluation.
      9. The extraction solvent used for this evaluation consisted of 1 µL of the appropriate internal standard per milliter of CS₂. CAUTION: extraction efficiency of the internal standard from the sampling medium has an effect on sample results. This effect is especially significant for SKC 575-002 Passive Samplers. Do not substitute internal standards unless extraction efficiencies are confirmed. Both internal standards can be present in the same extraction solvent if the appropriate internal standard is used to calibrate the GC, and to calculate sample results.
      10. GC grade nitrogen, air, and hydrogen were used in this evaluation.
   3. Standard preparation
      1. Prepare stock mixed standards by weighing 1-mL aliquots of all four analytes into the same container. For example: a neat mixed standard was prepared that contained 212.7 mg/mL of m-xylene, 212.6 mg/mL of o-xylene, 213.4 mg/mL of p-xylene, and 215.3 mg/mL of ethylbenzene.
      2. Prepare working range standards for the analysis of charcoal tubes by injecting microliter quantities of the stock mixed standard into 1-mL aliquots of extraction solvent (containing 1 µL p-cymene internal standard per milliter of CS₂). For example, a working range standard was prepared by injecting 6.0 µL of the stock mixed standard into extraction solvent. This standard contained 1276 µg/mL of m-xylene, 1276 µg/mL of o-xylene, 1280 µg/mL of p-xylene, and 1292 µg/mL of ethylbenzene.
      3. Prepare working range standards for the analysis of SKC 575-002 Passive Samplers by first diluting the stock mixed standard (Section 3.4.1) 1 to 4 with CS₂, and then injecting microliter quantities of the diluted stock mixed standard into 2-mL aliquots of extraction solvent (containing 1 µL 1-phenylhexane internal standard per milliter of CS₂). For example, a working range standard was prepared by injecting 6.0 µL of the diluted stock mixed standard into extraction solvent. This standard contained 319.0 µg/mL of m-xylene, 318.9 µg/mL of o-xylene, 320.1 µg/mL of p-xylene, and 323.0 µg/mL of ethylbenzene.
      4. Prepare a sufficient number of standards so that sample results will likely be bracketed with standards. If sample results are outside the range of prepared standards, prepare and analyze additional standards, or dilute high samples with extraction solvent and then reanalyze the diluted samples.
   4. Sample preparation
      1. Charcoal tubes

         Remove the plastic end caps from the sampling tube and carefully transfer each section of the adsorbent into separate 2-mL glass vials. Check to be certain that no charcoal is trapped in the glass-wool plug. Discard the end caps, glass tube, glass wool plug, and foam plugs.

         Add 1.0 mL of extraction solvent to each vial and immediately seal each vial with a PTFE-lined septum cap.

         Shake the vials vigorously several times during the one-hour extraction time.

      2. SKC 575-002 Passive Samplers

         Cut off the ends of the two protruding tubes of each sampler with a razor blade or a sharp knife.

         Secure the sampler by clipping it to a rail of the detachable SKC Desorption Shaker rack. Carefully and slowly add 2.0 mL of extraction solvent through the protruding tube nearest the outside edge of the sampler using a volumetric pipet. The tip of the pipet should fit just inside the sampler tube. Immediately seal the sampler tubes with the plugs supplied by the manufacturer.

         Replace the rack onto the SKC Desorption Shaker and shake the samples for one hour.

         Do not allow the extracted sample to remain in the sampler. Transfer the extracted sample into 2-mL glass vials by removing the plugs from the protruding tubes, inserting the tapered end of the PTFE tube supplied by the manufacture into the protruding tube nearest the outside edge of the sampler, and carefully pouring the solution into a 2-mL glass vial. Immediately seal the vials with PTFE-lined septum caps.

   5. Analysis
      1. GC conditions

         zone temperatures:	column	40 °C, hold 1 min, program at 4 °C/min to 140 °C, and hold as necessary to clear column
         	injector	220 °C
         	detector	220 °C
         gas flows:	hydrogen (carrier)	4.4 mL/min (115 kPa head pressure)
         	nitrogen (makeup)	38 mL/min
         	hydrogen (FID)	35 mL/min
         	air (FID)	455 mL/min
         signal range:		3
         injection volume:		1 µL (20:1 split)
         column:		60 m × fused silica 0.32-mm i.d. DB Wax 0.5-µm df

         

         Figure 3.5.1 Chromatogram of a sample desorbed from charcoal. Concentration is approximately the 100-ppm PEL for each analyte. Key: (1) CS₂, (2) ethylbenzene, (3) p-xylene, (4) m-xylene, (5) o-xylene, (6) p-cymene, (7) 1-phenylhexane.

      2. Measure peak areas with an electronic integrator or other suitable means.
      3. An internal standard (ISTD) method is used to calibrate the instrument in terms of micrograms of analyte per sample. Prepare a calibration curve by analyzing standards, and constructing calibration curves by plotting ISTD-corrected detector response versus mass of analyte. Bracket sample results with standards.
         

         Figure 3.5.3.1 Calibration curve for m-xylene standards used to analyze charcoal tubes constrcted from the data in Table 4.3.1.

         

         Figure 3.5.3.2 Calibration curve for m-xylene standards used to analyze SKC 575-002 Passive Samplers constructed from the data in Table 4.3.5.

         

         Figure 3.5.3.3 Calibration curve for o-xylene standards used to analyze charcoal tubes constructed from the data in Table 4.3.2.

         

         Figure 3.5.3.4 Calibration curve for o-xylene standards used to analyze SKC 575-002 Passive Samplers constructed from the data in Table 4.3.6.

         

         Figure 3.5.3.5 Calibration curve for p-xylene standards used to analyze charcoal tubes constructed from the data in Table 4.3.3.

         

         Figure 3.5.3.6 Calibration curve for p-xylene standards used to analyze SKC 575-002 Passive Samplers constructed from the data in Table 4.3.7.

         

         Figure 3.5.3.7 Calibration curve for ethylbenzene standards used to analyze charcoal tubes constructed from the data in Table 4.3.4.

         

         Figure 3.5.3.8 Calibration curve for ethylbenzene standards used to analyze SKC 575-002 Passive Samplers constructed from the data in Table 4.3.8.

   6. Interferences (analytical)
      1. Any chemical that produces an FID response and has a similar retention time as any of the analytes or internal standard is a potential interference. Any reported potential interferences should be considered before samples are extracted. Generally, chromatographic conditions can be altered to separate an interference from an analyte or an internal standard.
      2. The identity or purity of an analyte peak can be confirmed with additional analytical data. (Section 4.10)
   7. Calculations
      1. Charcoal tubes

         Obtain separate amounts of each analyte (m-xylene, o-xylene, p-xylene, ethylbenzene) per sample from the appropriate calibration curve in terms of micrograms per sample. These amounts are uncorrected for extraction efficiency. Be certain that the correct internal standard was used to calculate results (See Section 3.2.9). The back section of the sampling tube is analyzed primarily to determine the extent of sampler saturation. If any analyte is found on the back section, it is added to the amount found on the front section. This amount is then corrected by subtracting the total amount (if any) found on the blank. The air concentrations are then calculated using the following formulas. Calculate xylenes exposure by summing the individual xylene isomer results.

         mg/m3   =

         micrograms of analyte per sample liters of air sampled × extraction efficiency

         ppm   =

         24.46 × mg/m3 106.17

         Where

         24.46 is the molar volume at 25 °C and 101.3 kPa (760 mmHg) 106.17 is the molecular weight of m-xylene, o-xylene, p-xylene, and ethylbenzene

      2. SKC 575-002 Passive Samplers

         Obtain separate amounts of each analyte (m-xylene, o-xylene, p-xylene, ethylbenzene) per sample from the appropriate calibration curve in terms of micrograms per sample. These amounts are uncorrected for extraction efficiency. Be certain that the correct internal standard was used to calculate results. This amount is then corrected by subtracting the amount (if any) found on the blank.

         Table 3.7.2
         Sampling Rates for SKC 573-002 Passive
         Samplers (mL/min) at 760 mmHg and 25 °C

         m-xylene	o-xylene	p-xylene	ethylbenzene
         13.82	14.24	13.94	13.83

         Sampling time, sampling site temperature (°C), and sampling site pressure (mmHg) is information given by the person submitting the samples. Sampling rates at 760 mmHg and 25 °C (SR_NTP) are given in Table 3.7.2. These sampling rates must be converted to their equivalent (SR_amb) at sampling site temperature (T) and sampling site pressure (P) by the following formula:

         SR amb

         =

         ( SRNTP)

         [

         T+273 298

         ]

         1.5

         [

         760 P

         ]

         Assume sampling site temperature is 22.2 °C if it is not given. If sampling site pressure is not given, it can be calculated by the following formula:

         P = ( 3.887 × 10^-7 ) E² - ( 2.7467 × 10^-2 ) E + 760

         Where

         P is the approximate sampling site barometric pressure. E is the sampling site elevation.

         E can be estimated from airports near the sampling site location using a web site such as AirNav.com

         Liters of air sampled is calculated by multiplying the appropriate SR_amb by sampling time and dividing that result by 1000.

         Air concentrations are then calculated using the following formulas. Calculate xylenes exposure by summing the individual xylene isomer results.

         mg/m3 =

         micrograms of analyte per sample liters of air sampled × extraction efficiency

         ppm =

         24.46 × mg/m3 106.17

         Where

         24.46 is the molar volume at 25 °C and 101.3 kPa (760 mmHg) 106.17 is the molecular weight of m-xylene, o-xylene, p-xylene, and ethylbenzene

4. Backup Data

   General background information about determination of detection limits and precision of the overall procedure is found in OSHA SLTC "Evaluation Guidelines for Air Sampling Methods Utilizing Chromatographic Analysis"²². The Guidelines define analytical parameters and specify required laboratory tests, statistical calculations and acceptance criteria.

   1. Detection limit of the analytical procedure (DLAP)

      The DLAP is measured as the mass of analyte introduced into the chromatographic column. Ten standards were prepared in equal descending increments of analyte, such that the highest standard produced a peak approximately 10 times the response of a reagent blank. These standards, and a reagent blank, were analyzed using the recommended analytical parameters (1-µL injection with a 20:1 split), and the data obtained were used to determine the required parameters (A and SEE_DL) for the calculation of the DLAP. Xylenes DLOP was calculated by summing masses and areas for individual xylene isomers. The extraction solvent contained a contaminant that eluted at the same time as p-xylene. The amount of this contaminant was small, but sufficient to cause a higher DLAP for p-xylene than for the other analytes.

      Table 4.1
      Detection Limit of the
      Analytical Procedure

      analyte	DLAP (pg)
      xylenes m-xylene o-xylene p-xylene ethylbenzene	14.5  2.1 8.4 14.0  5.7

      Table 4.1.1
      DLAP for Xylenes

      concn (ng/mL)	mass on column (pg)	area counts (µV-s)
      0 512 1026 1538 2052 2564 3076 3590 4102 4616 5128	0 25.6 51.3 76.9 102.6 128.2 153.8 179.5 205.1 230.8 256.4	150 196 284 369 395 482 566 636 697 769 853

      

      Figure 4.1.1 Plot of data used to determine DLAP for xylenes.

      Table 4.1.2
      DLAP for m-Xylene

      concn (ng/mL)	mass on column (pg)	area counts (µV-s)
      0 170 342 512 684 854 1024 1196 1366 1538 1708	0 8.5 17.1 25.6 34.2 42.7 51.2 59.8 68.3 76.9 85.4	8 32 52 80 102 123 145 168 196 215 240

      

      Figure 4.1.2 Plot of data used to determine DLAP for m-xylene.

      Table 4.1.3
      DLAP for o-Xylene

      concn (ng/mL)	mass on column (pg)	area counts (µV-s)
      0 172 342 514 684 856 1028 1198 1370 1540 1712	0 8.6 17.1 25.7 34.2 42.8 51.4 59.9 68.5 77.0 85.6	0 21 37 81 85 120 143 171 174 231 235

      

      Figure 4.1.3 Plot of data used to determine DLAP for o-xylene.

      Table 4.1.4
      DLAP for p-Xylene

      concn (ng/mL)	mass on column (pg)	area counts (µV-s)
      0 170 342 512 684 854 1024 1196 1366 1538 1708	0 8.5 17.1 25.6 34.2 42.7 51.2 59.8 68.3 76.9 85.4	142 143 195 208 208 239 278 297 327 323 368

      

      Figure 4.1.4 Plot of data used to determine DLAP for p-xylene.

      Table 4.1.5
      DLAP for Ethylbenzene

      concn (ng/mL)	mass on column (pg)	area counts (µV-s)
      0 174 346 520 692 866 1040 1212 1386 1558 1732	0 8.7 17.3 26.0 34.6 43.3 52.0 60.6 69.3 77.9 86.6	0 26 38 66 92 120 146 165 177 206 233

      

      Figure 4.1.5 Plot of data used to determine DLAP for ethylbenzene.

   2. Detection limit of the overall procedure (DLOP) and reliable quantitation limit (RQL)

      The DLOP is measured as mass per sample and expressed as equivalent air concentrations, based on the recommended sampling parameters. Ten 100-mg portions of SKC Lot 2000 charcoal, and ten 500-mg portions of SKC Anasorb 747, (representing SKC 575-002 Passive Samplers) were spiked with equal descending increments of analyte, such that the highest sampler loading would produce a peak approximately 10 times the response for a sample blank. These spiked samples, and sample blanks were analyzed with the recommended analytical parameters, and the data obtained used to calculate the required parameters (A and SEE_DL) for the calculation of DLOP and RQL. Xylenes DLOP and RQL were calculated by summing masses and areas for individual xylene isomers. Sample air volume and extraction efficiency for xylenes is the mean of those for individual xylene isomers. Table 4.2 is a summary of DLOP results and is presented for quick reference.

      Table 4.2
      Detection Limit of the Overall Procedure Summary

      analyte	charcoal tubes			SKC 575-002 Passive Samplers
      	ng	µg/m3	ppb	ng	µg/m3	ppb
      xylenes m-xylene o-xylene p-xylene ethylbenzene	322 159 239 100 129	26.8 13.2 19.9   8.3 10.8	6.2 3.0 4.6 1.9 2.5	847 448 325 437 315	252.8 134.9 95.0 130.8 94.9	58.2 31.1 21.9 30.1 21.9

      Table 4.2.1
      DLOP and RQL
      for Xylenes from Charcoal Tubes

      mass per sample (ng)	area counts (µV-s)
      0 513 1025 1538 2051 2563 3076 3590 4101 4614 5128	139 238 272 357 423 485 524 624 691 763 835

      

      Figure 4.2.1 Plot of data used to determine DLOP and RQL for xylenes.

      Table 4.2.2
      DLOP and RQL for Xylenes
      from SKC 575-002 Passive Samplers

      mass per sample (ng)	area counts (µV-s)
      0 1025 2051 3076 4101 5128 6152 7179 8204 9228 10255	136 247 278 334 452 497 588 615 696 769 844

      

      Figure 4.2.2 Plot of data used to determine DLOP and RQL for xylenes.

      Table 4.2.3
      DLOP and RQL
      for m-Xylene from Charcoal Tubes

      mass per sample (ng)	area counts (µV-s)
      0 171 341 512 683 853 1024 1195 1365 1536 1707	0 39 54 74 109 116 134 168 200 215 239

      

      Figure 4.2.3 Plot of data used to determine DLOP and RQL for m-xylene.

      Table 4.2.4
      DLOP and RQL for m-Xylene
      from SKC 575-002 Passive Samplers

      mass per sample (ng)	area counts (µV-s)
      0 341 683 1024 1365 1707 2048 2390 2731 3072 3414	0 46 56 61 110 116 158 175 194 226 237

      

      Figure 4.2.4 Plot of data used to determine DLOP and RQL for m-xylene.

      Table 4.2.5
      DLOP and RQL
      for o-Xylene from Charcoal Tubes

      mass per sample (ng)	area counts (µV-s)
      0 171 343 514 685 857 1028 1200 1371 1542 1714	0 31 39 70 85 121 115 161 168 210 239

      

      Figure 4.2.5 Plot of data used to determine DLOP and RQL for o-xylene.

      Table 4.2.6
      DLOP and RQL for o-Xylene from
      SKC 575-002 Passive Samplers

      mass per sample (ng)	area counts (µV-s)
      0 343 685 1028 1371 1714 2056 2399 2742 3084 3427	0 29 35 69 96 112 126 147 164 190 223

      

      Figure 4.2.6 Plot of data used to determine DLOP and RQL for o-xylene.

      Table 4.2.7
      DLOP and RQL
      for p-Xylene from Charcoal Tubes

      mass per sample (ng)	area counts (µV-s)
      0 171 341 512 683 853 1024 1195 1365 1536 1707	139 168 179 213 229 248 275 295 323 338 357

      

      Figure 4.2.7 Plot of data used to determine DLOP and RQL for p-xylene.

      Table 4.2.8
      DLOP and RQL for p-Xylene from
      SKC 575-002 Passive Samplers

      mass per sample (ng)	area counts (µV-s)
      0 341 683 1024 1365 1707 2048 2390 2731 3072 3414	136 172 187 204 246 269 304 293 338 353 384

      

      Figure 4.2.8 Plot of data used to determine DLOP and RQL for p-xylene.

      Table 4.2.9
      DLOP and RQL
      for Ethylbenzene from Charcoal Tubes

      mass per sample (ng)	area counts (µV-s)
      0 173 346 519 692 865 1038 1211 1384 1558 1731	0 35 44 76 88 118 136 153 182 198 231

      

      Figure 4.2.9 Plot of data used to determine DLOP and RQL for ethylbenzene.

      Table 4.2.10
      DLOP and RQL for Ethylbenzene from
      SKC 575-002 Passive Samplers

      mass per sample (ng)	area counts (µV-s)
      0 346 692 1038 1384 1731 2077 2423 2769 3115 3461	0 25 52 71 90 111 143 153 186 212 251

      

      Figure 4.2.10 Plot of data used to determine DLOP and RQL for ethylbenzene.

      The RQL is considered the lower limit for precise quantitative measurements. It is determined from the regression line parameters obtained for calculation of DLOP, providing the extraction efficiency (EE) is 100 ± 25% at the RQL.

      Table 4.2.11
      Reliable Quantitation Limits

      analyte	charcoal tubes				SKC 575-002 Passive Samplers
      	ng	µg/m3	ppb	EE(%)	ng	µg/m3	ppb	EE(%)
      xylenes m-xylenes o-xylenes p-xylenes ethylbenzene	1072 531 795 334 431	89.3 44.2 66.2 27.8 35.9	20.6 10.2 15.3 6.4 8.3	98.4 98.9 95.6 99.9 99.4	2823 1495 1084 1456 1049	842.7 450.3 317.0 435.9 316.0	194.1 103.7 73.0 100.4 72.8	93.6 96.4 84.9 95.6 97.6

      

      Figure 4.2.11 Chromatogram of a sample containing masses of analytes approximating the RQLs extracted from a charcoal tube. Key: (1) ethylbenzene, (2) p-xylene, (3) m-xylene, (4) o-xylene.

      

      Figure 4.2.12 Chromatogram of a sample containing masses of analytes approximating the RQLs extracted from a SKC 575-002 Passive Sampler. Key: (1) ethylbenzene, (2) p-xylene, (3) m-xylene, (4) o-xylene.

   3. Instrument calibration

      Table 4.3
      Coefficient of Determination (r²)
      and of Nondetermination (k²)

      analyte	charcoal tubes		SKC 575-002 Pass Sampers
      	r2	k2	r2	k2
      m-xylene	0.9994	6 × 10-4	0.9998	2 × 10-4
      o-xylene	0.9995	5 × 10-4	0.9998	2 × 10-4
      p-xylene	0.9994	6 × 10-4	0.9998	2 × 10-4
      ethylbenzene	0.9994	6 × 10-4	0.9998	2 × 10-4

      The instrument was calibrated for xylene isomers and ethylbenzene over a range of from 0.5 to 2 times the 100 ppm PEL for each analyte. Calibration was performed at concentrations appropriate for both active and diffusive samplers. Calibration curves were constructed from the tabulated data and are shown in Section 3.5.3. Coefficients of determination (r²) and of nondetermination (k²) are shown in Table 4.3.

       

       

       

       

       

      Table 4.3.1
      Instrument Response to
      m-Xylene for Charcoal Tubes

      × OSHA PEL (µg/sample)	0.5× 2568	0.75× 3852	1× 5136	1.5× 7704	2× 10272
      area (µV-s)	164794 164754 164983 164992 165047 165182	269791 269445 269434 269351 269191 268965	375905 375908 376753 376901 375901 375624	593689 592710 593187 592430 591644 593035	783759 784944 786776 784541 784130 783251

      Table 4.3.2
      Instrument Response to
      o-Xylene for Charcoal Tube

      × OSHA PEL (µg/sample)	0.5× 2590	0.75× 3884	1× 5179	1.5× 7769	2× 10358
      area (µV-s)	167753 167760 167934 167902 167961 168094	274897 274708 274660 274497 274406 274212	383480 383480 384309 384433 383472 383231	606183 605143 605576 605029 604460 605477	801612 802500 804231 802144 801744 800999

      Table 4.3.3
      Instrument Response to
      p-Xylene for Charcoal Tubes

      × OSHA PEL (µg/sample)	0.5× 2559	0.75× 3839	1× 5118	1.5× 7678	2× 10237
      area (µV-s)	164552 164539 164734 164768 164807 164923	268846 268538 268527 268449 268265 268051	374277 374271 375116 375271 374253 374021	590454 589602 590062 589284 588468 589848	779090 780366 782170 779941 779572 778654

      Table 4.3.4
      Instrument Response to
      Ethylbenzene for Charcoal Tubes

      × OSHA PEL (µg/sample)	0.5× 2608	0.75× 3912	1× 5216	1.5× 7824	2× 10432
      area (µV-s)	164275 164292 164473 164518 164581 164665	269560 269199 269224 269089 268885 268679	375888 375846 376676 376857 375780 375508	593883 593063 593502 592685 591749 593173	783759 785278 787146 784787 784405 783391

      Table 4.3.5
      Instrument Response to m-Xylene
      for SKC 575-002 Passive Samplers

      × OSHA PEL (µg/sample)	0.5× 749	0.75× 1177	1× 1455	1.5× 2140	2× 2889
      area (µV-s)	29838 29955 29857 29887 29836 29842	47626 47689 47832 47847 47796 47774	58960 59183 59046 59397 59004 59284	86200 86119 86097 85956 85933 85854	117788 117903 117765 118128 117561 117760

      Table 4.3.6
      Instrument Response to o-Xylene
      for SKC 575-002 Passive Samplers

      × OSHA PEL (µg/sample)	0.5× 755	0.75× 1187	1× 1467	1.5× 2158	2× 2913
      area (µV-s)	30464 30579 30508 30521 30486 30483	48643 48697 48848 48880 48780 48795	60209 60434 60309 60692 60248 60531	88024 87973 87915 87801 87757 87695	120324 120516 120317 120670 120081 120298

      Table 4.3.7
      Instrument Response to p-Xylene
      for SKC 575-002 Passive Samplers

      × OSHA PEL (µg/sample)	0.5× 746	0.75× 1173	1× 1450	1.5× 2133	2× 2879
      area (µV-s)	29754 29867 29774 29817 29771 29772	47433 47507 47680 47672 47625 47597	58707 58961 58809 59157 58765 59041	85808 85716 85692 85590 85545 85468	117229 117319 117199 117578 116981 117192

      Table 4.3.8
      Instrument Response to Ethylbenzene
      for SKC 575-002 Passive Samplers

      × OSHA PEL (µg/sample)	0.5× 761	0.75× 1195	1× 1478	1.5× 2173	2× 2934
      area (µV-s)	29797 29920 29824 29882 29834 29816	47592 47668 47822 47826 47764 47738	58904 59197 59043 59390 58958 59261	86193 86089 86057 85970 85917 85830	117774 117857 117737 118148 117530 117767

   4. Precision (overall procedure)
      1. Charcoal tubes

         Table 4.4.1
         SEEs and Precisions of the
         Overall Procedure for Charcoal Tubes

         analyte	SEE(%)	precision(±%)
         xylenes m-xylene o-xylene p-xylene ethylbenzene	5.50 5.45 5.59 5.67 5.41	10.8 10.7 11.0 11.1 10.6

         The precision at the 95% confidence level is obtained by multiplying the SEE by 1.96 (the z-statistic from the standard normal distribution at the 95% confidence level). In Section 4.5, 95% confidence intervals are drawn about their respective regression lines in the storage graph figures. The precisions of the overall procedure were obtained from the ambient temperature storage tests and are shown in Table 4.4.1.

      2. SKC 575-002 Passive Samplers

         The precision at the 95% confidence level is obtained by multiplying the SEE by 1.96 (the z-statistic from the standard normal distribution at the 95% confidence level). In Section 4.5, 95% confidence intervals are drawn about their respective regression lines in the storage graph figures. Each precision includes an additional 8.7% for sampling rate variability. There are different values given, depending on whether both, either, or neither temperature or atmospheric pressure are known at the sampling site. If the sampling-site temperature (T) is unknown, it is assumed to be 22.2 ± 15 °C (72 ± 27 °F) and a variability of ±7.7% is included. If the atmospheric pressure (P) is unknown, it is estimated from sampling-site elevation and a variability of ±3% is included. The precisions of the overall procedure are shown in Table 4.4.2.

         Table 4.4.2
         SEEs and Precisions of the Overall Procedure for SKC 575-002 Passive Samplers

         condition	xylenes		m-xylene		o-xylene		p-xylene		ethylbenzene
         	SEE (%)	precision (±%)	SEE (%)	precision (±%)	SEE (%)	precision (±%)	SEE (%)	precision (±%)	SEE (%)	precision (±%)
         both T and P known only T known only P known neither T nor P known	9.29 9.76 12.07 12.43	18.2 19.1 23.7 24.4	9.32 9.79 12.09 12.46	18.3 19.2 23.7 24.4	9.24 9.71 12.03 12.40	18.1 19.0 23.6 24.3	9.33 9.80 12.10 12.46	18.3 19.2 23.7 24.4	9.39 9.86 12.14 12.51	18.4 19.3 23.8 24.5

   5. Storage tests
      1. Charcoal tubes

         Storage stability samples were prepared by sampling (at 50 mL/min for four hours) dynamically generated test atmospheres of mixed xylenes with SKC 226-01 sampling tubes. These samples were collected simultaneously along with diffusive samples. The concentrations of the test atmospheres were 207 mg/m³ (48 ppm) for m-xylene, 96 mg/m³ (22 ppm) for o-xylene, 90 mg/m³ (21 ppm) for p-xylene, and 73 mg/m³ (17 ppm) for ethylbenzene at 83% relative humidity and 20 °C. Xylenes concentration was the sum of the individual isomers and was 393 mg/m³ (91 ppm). These air concentrations were approximately one times the target concentration for xylenes and were in the same proportions as were the analytes in the mixed xylenes used to generate the test atmospheres. Xylenes results were calculated from summed individual isomers results. Sample results are corrected for extraction efficiency.

         Table 4.5.1.1
         Storage Tests for Xylenes

         time (days)	ambient storage recovery (%)			refrigerated storage recovery (%)
         0 3 7 10 14 16	97.0 101.1 102.2 96.5 101.6 99.8	98.9 102.5 97.4 97.9 96.7 97.0	96.8 100.3 103.1 99.2 97.9 101.1	97.0 103.1 96.3 100.4 101.3 101.7	98.9 101.3 100.2 98.2 99.4 93.8	96.8 100.3 100.8 98.8 100.2 102.0

         Table 4.5.1.2
         Storage Tests for m-Xylene

         time (days)	ambient storage recovery (%)			refrigerated storage recovery (%)
         0 3 7 10 14 16	97.3 101.4 102.5 97.0 101.9 100.6	99.1 102.8 97.8 98.3 97.2 98.7	97.2 100.6 103.3 99.5 99.8 101.9	97.3 103.3 97.6 100.7 101.6 102.0	99.1 101.6 100.7 98.7 99.7 93.7	97.2 100.6 101.2 99.2 100.5 102.3

         Table 4.5.1.3
         Storage Tests for o-Xylene

         time (days)	ambient storage recovery (%)			refrigerated storage recovery (%)
         0 3 7 10 14 16	96.1 100.7 101.5 95.2 101.0 99.5	98.4 101.8 96.3 97.0 95.6 95.8	95.9 99.5 102.6 98.4 98.5 100.6	96.1 102.5 95.6 99.6 100.6 101.1	98.4 100.7 99.2 96.9 98.8 94.4	95.9 99.6 100.0 97.7 99.5 101.4

         Table 4.5.1.4
         Storage Tests for p-Xylene

         time (days)	ambient storage recovery (%)			refrigerated storage recovery (%)
         0 3 7 10 14 16	97.0 101.1 102.1 96.6 101.6 99.6	98.8 102.5 97.5 98.0 96.8 97.0	96.8 100.3 103.0 99.2 93.1 101.1	97.0 103.0 96.4 100.4 101.3 101.7	98.8 101.3 100.3 98.3 99.4 93.5	96.8 100.3 100.9 98.9 100.2 101.9

         Table 4.5.1.5
         Storage Tests for Ethylbenzene

         time (days)	ambient storage recovery (%)			refrigerated storage recovery (%)
         0 3 7 10 14 16	98.2 102.1 103.1 98.2 102.5 100.0	99.7 103.6 99.0 99.3 98.6 97.5	98.3 101.6 103.9 100.3 100.8 101.4	98.2 104.0 97.5 101.6 102.3 102.6	99.7 102.3 101.9 100.1 100.6 93.5	98.3 101.3 102.2 100.3 101.2 103.0

         

         Figure 4.5.1.1 Ambient storage test for xylenes collected on charcoal tubes.

         

         Figure 4.5.1.2 Regrigerated storage test for xylenes collected on charcoal tubes.

         

         Figure 4.5.1.3 Ambient storage test for m-xylene collected on charcoal tubes.

         

         Figure 4.5.1.4 Regrigerated storage test for m-xylene collected on charcoal tubes.

         

         Figure 4.5.1.5 Ambient storage test for o-xylene collected on charcoal tubes.

         

         Figure 4.5.1.6 Regrigerated storage test for o-xylene collected on charcoal tubes.

         

         Figure 4.5.1.7 Ambient storage test for p-xylene collected on charcoal tubes.

         

         Figure 4.5.1.8 Regrigerated storage test for p-xylene collected on charcoal tubes.

         

         Figure 4.5.1.9 Ambient storage test for ethylbenzene collected on charcoal tubes.

         

         Figure 4.5.1.10 Regrigerated storage test for ethylbenzene collected on charcoal tubes.

      2. SKC 575-002 Passive Samplers

         Storage stability samples were prepared by sampling dynamically generated test atmospheres of mixed xylenes with SKC 575-002 Passive Samplers. The face velocity of the test atmosphere was about 0.4m/s past the diffusive samplers. The samplers were orientated parallel to the flow direction. These samples were collected for four hours simultaneously along with active samples under conditions described in Section 4.5.1. Xylenes results were calculated from summed isomers results. Sample results are corrected for extraction efficiency.

         Table 4.5.2.1
         Storage Tests for Xylenes

         time (days)	ambient storage recovery (%)			refrigerated storage recovery (%)
         0 3 7 10 14 16	96.6 101.0 104.6 101.1 98.0 97.4	97.3 101.6 93.5 102.8 92.9 98.9	97.1 102.5 99.7 97.2 99.7 94.4	96.6 101.2 100.9 100.5 100.6 102.4	97.3 102.5 100.0 99.5 99.4 100.9	97.1 101.4 98.6 100.7 100.5 97.9

         Table 4.5.2.2
         Storage Tests for m-Xylene

         time (days)	ambient storage recovery (%)			refrigerated storage recovery (%)
         0 3 7 10 14 16	96.8 101.5 105.1 101.6 98.4 97.9	97.5 102.2 93.9 103.3 93.3 99.4	97.4 103.1 100.2 97.6 100.1 94.9	96.8 101.8 101.3 100.9 101.1 102.9	97.5 103.1 100.4 100.0 99.9 101.4	97.4 101.9 99.0 101.1 101.0 98.4

         Table 4.5.2.3
         Storage Tests for o-Xylene

         time (days)	ambient storage recovery (%)			refrigerated storage recovery (%)
         0 3 7 10 14 16	96.2 99.7 103.4 99.9 96.9 96.2	96.8 100.4 92.4 101.5 92.1 97.7	96.6 101.1 98.6 96.1 99.0 93.1	96.2 99.7 99.9 99.4 99.3 101.1	96.8 101.1 98.8 98.4 98.2 99.6	96.6 100.4 97.3 99.6 99.3 96.7

         Table 4.5.2.4
         Storage Tests for p-Xylene

         time (days)	ambient storage recovery (%)			refrigerated storage recovery (%)
         0 3 7 10 14 16	96.6 101.2 104.8 101.3 98.1 97.5	97.2 101.8 93.6 103.1 92.9 99.1	97.0 102.8 99.9 97.3 99.6 94.5	99.6 101.5 101.0 100.6 100.7 102.5	97.2 102.8 100.2 99.7 99.5 101.0	97.0 101.5 98.7 100.8 100.7 98.0

         Table 4.5.2.5
         Storage Tests for Ethylbenzene

         time (days)	ambient storage recovery (%)			refrigerated storage recovery (%)
         0 3 7 10 14 16	97.4 103.0 106.5 103.0 99.6 99.1	98.1 103.6 95.2 104.7 94.3 100.8	98.0 104.4 101.5 98.8 101.0 96.1	97.4 103.2 102.6 102.2 102.7 104.4	98.1 104.4 101.7 101.3 101.2 102.9	98.0 103.5 100.4 102.4 102.4 99.7

         

         Figure 4.5.2.1 Ambient storage test for xylenes collected on SKC 575-002 Passive Samplers.

         

         Figure 4.5.2.2 Regrigerated storage test for xylenes collected on SKC 575-002 Passive Samplers.

         

         Figure 4.5.2.3 Ambient storage test for m-xylene collected on SKC 575-002 Passive Samplers.

         

         Figure 4.5.2.4 Regrigerated storage test for m-xylene collected on SKC 575-002 Passive Samplers.

         

         Figure 4.5.2.5 Ambient storage test for o-xylene collected on SKC 575-002 Passive Samplers.

         

         Figure 4.5.2.6 Regrigerated storage test for o-xylene collected on SKC 575-002 Passive Samplers.

         

         Figure 4.5.2.7 Ambient storage test for p-xylene collected on SKC 575-002 Passive Samplers.

         

         Figure 4.5.2.8 Regrigerated storage test for p-xylene collected on SKC 575-002 Passive Samplers.

         

         Figure 4.5.2.9 Ambient storage test for ethylbenzene collected on SKC 575-002 Passive Samplers.

         

         Figure 4.5.2.10 Regrigerated storage test for ethylbenzene collected on SKC 575-002 Passive Samplers.

   6. Reproducibility

      Twelve samples (six charcoal tubes and six SKC 575-002 Passive Samplers) were collected from controlled test atmospheres similar to that used to collect storage stability samples. The samples were submitted to SLTC for analysis. The charcoal tube samples were analyzed after 16 days of storage at ambient temperature, and the SKC 575-002 Passive Samplers after 22 days of storage at ambient temperature. Sample results were corrected for extraction efficiency. No sample result had a deviation greater than the precision of the overall procedure reported in Section 4.4. Xylenes results were calculated by summing results for individual isomers.

      Table 4.6.1
      Reproducibility Data for Xylene Isomers on Charcoal Tubes

      m-xylene				o-xylene				p-xylene
      theo	reported	recovery	deviation	theo	reported	recovery	deviation	theo	reported	recovery	deviation
      µg/samp	µg/samp	(%)	(%)	µg/samp	µg/samp	(%)	(%)	µg/samp	µg/samp	(%)	(%)
      2555 2595 2623 2557 2564 2623	2552 2593 2427 2580 2593 2610	99.9 99.9 92.5 100.9 101.1 95.5	-0.1 -0.1 -7.5 0.9 1.1 -0.5	1189 1207 1221 1190 1193 1221	1245 1266 1158 1262 1263 1275	104.7 104.9 94.8 106.1 105.9 104.4	4.7 4.9 -5.2 6.1 5.9 4.4	1112 1129 1142 1129 1116 1142	1140 1158 1082 1152 1159 1166	102.5 102.6 94.7 102.0 103.9 102.1	2.5 2.6 -5.3 2.0 3.9 2.1

      Table 4.6.2
      Reproducibility Data for Xylenes and Ethylbenzene on Charcoal Tubes

      xylenes				| | |	ethylbenzene
      theo µg/samp	reported µg/samp	recovery (%)	deviation (%)		theo µg/samp	reported µg/samp	recovery (%)	deviation (%)
      4856 4931 4986 4876 4873 4986	4937 5017 4667 4994 5014 5051	101.7 101.7 93.6 102.4 102.9 101.3	1.7 1.7 -6.4  2.4 2.9 1.3	| | | | | |	904.8 918.9 929.0 905.6 911.8 929.0	929.4 944.2 895.4 939.1 945.6 944.3	102.7 102.8 96.4 103.7 103.7 101.6	2.7 2.8 -3.6  3.7 3.7 1.6

      Table 4.6.3
      Reproducibility Data for Xylene Isomers on SKC 575-002
      Passive Samplers

      m-xylene				o-xylene				p-xylene
      theo	reported	recovery	deviation	theo	reported	recovery	deviation	theo	reported	recovery	deviation
      µg/samp	µg/samp	(%)	(%)	µg/samp	µg/samp	(%)	(%)	µg/samp	µg/samp	(%)	(%)
      847.6 847.6 847.6 847.6 847.6 847.6	859.1 823.9 811.5 806.0 805.5 803.3	101.4 97.2 95.7 95.1 95.0 94.8	1.4 -2.8 -4.3 -4.9 -5.0 -5.2	401.3 401.3 401.3 401.3 401.3 401.3	430.8 417.1 408.8 399.0 406.3 398.9	107.4 103.9 101.9 99.4 101.2 99.4	7.4 3.9 1.9 -0.6 1.2 -0.6	372.8 372.8 372.8 372.8 372.8 372.8	404.9 389.1 383.0 381.0 380.2 380.4	108.6 104.4 102.7 102.2 102.0 102.0	8.6 4.4 2.7 2.2 2.0 2.0

      Table 4.6.4
      Reproducibility Data for Xylenes and Ethylbenzene on SKC 575-002 Passive Samplers

      xylenes				| | |	ethylbenzene
      theo µg/samp	reported µg/samp	recovery (%)	deviation (%)		theo µg/samp	reported µg/samp	recovery (%)	deviation (%)
      1622 1622 1622 1622 1622 1622	1695 1630 1603 1586 1592 1583	104.5 100.5 98.8 97.8 98.2 97.6	4.5 0.5 -1.2 -2.2 -1.8 -2.4	| | | | | |	302.3 302.3 302.3 302.3 302.3 302.3	312.2 298.3 293.9 295.0 291.7 293.7	103.3 98.7 97.2 97.6 96.5 97.2	3.3 -1.3 -2.8 -2.4 -3.5 -2.8

   7. Sampler capacity
      1. Charcoal tubes

         The sampling capacity of charcoal tubes was tested by sampling dynamically generated test atmospheres of mixed xylenes with SKC 226-01 (Lot 2000) sampling tubes. These samples were collected simultaneously along with diffusive samples. The sampling times were 5, 10, 15, and 30 min; and 1, 2, 3, 4, 6, 8, and 10 hours. Three active and three diffusive samples were collected for each time period. The mean concentrations of the test atmospheres were 456 mg/m³ (105 ppm) for m-xylene, 212 mg/m³ (49 ppm) for o-xylene, 198 mg/m³ (46 ppm) for p-xylene, and 161 mg/m³ (37 ppm) for ethylbenzene at 78% relative humidity and 21 °C. These air concentrations were approximately two times the target concentration for xylenes and were in the same proportions as were the analytes in the mixed xylenes used to generate the test atmospheres. No breakthrough from the front to the back section of the sampling tubes for any of the analytes was observed even when samples were collected for ten hours at 50 mL/min. Sampler capacity was never exceeded. Nearly 31 mg of mixed xylenes had been collected after ten hours. The recommended sampling time was set at four hours and the recommended sampling rate at 50 mL/min. These tests also showed that samples can be collected for as short a time as 5 min at 50 mL/min and still provide excellent results.

      2. SKC 575-002 Passive Samplers

         The sampling rate and sampler capacity of SKC 575-002 Passive Samplers were determined with samples collected at the increasing time intervals from the controlled test atmospheres described in Section 4.7.1. The face velocity of the test atmosphere was approximately 0.4 m/s, and the samplers were orientated parallel to the flow direction. Three samples were collected at each time interval. Sampler capacity has been defined to be exceeded when the "apparent" sampling rate decreases rapidly. The sampling rate only appears to decrease because the sampler can collect no additional analyte at the point when capacity is exceeded. Sampling rates are presented in mL/min at 760 mmHg and 25 °C.

         Table 4.7.2
         Determination of Sampling Rate and Recommended Sampling Time

         time	m-xylene		o-xylene		p-xylene		ethylbenzene
         (h)	mL/min	RSD	mL/min	RSD	mL/min	RSD	mL/min	RSD
         0.083	13.75	2.2	14.25	3.8	13.99	2.8	13.85	2.3
         0.167	13.53	1.4	13.97	1.3	13.71	1.8	13.68	1.5
         0.25	13.91	0.9	14.38	0.9	14.01	0.9	13.96	0.8
         0.5	13.94	1.6	14.39	2.4	14.07	1.7	13.93	1.2
         1	13.81	2.1	14.17	2.4	13.94	2.2	13.86	2.2
         2	13.55	1.7	13.79	1.8	13.59	1.7	13.50	2.0
         3	14.01	1.4	14.27	1.4	14.04	1.4	13.96	1.5
         4	13.60	0.6	14.93	0.9	13.67	0.7	13.59	0.6
         6	14.20	5.0	14.40	5.0	14.48	5.0	14.19	5.0
         8	13.60	0.2	13.70	0.1	13.70	0.2	13.59	0.2
         10	14.11	2.6	14.35	2.5	14.16	2.7	14.06	2.6
         mean	13.82		14.24		13.94		13.83
         RSD	1.7		2.4		1.9		1.6

         The preliminary sampling rate was determined by averaging the values for the 0.5, 1, and 2 hour samples. Horizontal lines were constructed 10% above and 10% below the preliminary sampling rate. All the sampling rates were included in the calculated mean sampling rates because all were between the two horizontal lines.

         

         Figure 4.7.2.1 Sampler capacity data for m-xylene.

         

         Figure 4.7.2.2 Sampler capacity data for o-xylene.

         

         Figure 4.7.2.3 Sampler capacity data for p-xylene.

         

         Figure 4.7.2.4 Sampler capacity data for ethylbenzene.

   8. Extraction efficiency and stability of extracted samples

      Each laboratory must determine and confirm extraction efficiency periodically. Other solvents can be used in conjunction with this method provided the new solvent is tested. The new solvent should be tested as described below and the extraction efficiency must be greater than 75%.

      A summary of the extraction efficiency results over the range of RQL to 2 times the target concentration is presented in Table 4.8 for quick reference.

      Table 4.8
      Extraction Efficiency (%) Summary

      analyte	charcoal tubes	SKC 575-002 Passive Samplers
      m-xylene	96.3	96.1
      o-xylene	93.8	89.4
      p-xylene	96.1	95.3
      ethylbenzene	97.2	99.1

      1. Charcoal tubes

         The extraction efficiencies (EEs) of the analytes were determined by liquid-spiking 100-mg portions of SKC Lot 2000 charcoal with the analytes at levels from the RQL to 2 times the OSHA PEL for each analyte. These samples were stored overnight at ambient temperature, and then extracted with 1mL of CS₂ (containing 1 µL of p-cymene per mL of CS₂) for 1 hour. The samples were vigorously shaken periodically over the extraction time. The EEs of the analytes at the target concentration were also determined from "wet" charcoal to confirm that EE remained constant. Wet charcoal was prepared by collecting samples from a humid (about 80% RH and 22 °C) atmosphere at 50 mL/min for 4 hours. Only the front section of these samples was used to prepare wet EE samples. The stability of extracted samples was investigated by reanalyzing the 1 × PEL samples a day after the original analysis. Three vials were immediately resealed with new septa caps and three vials retained their punctured septa following the original analysis.

         Table 4.8.1.1
         Extraction Efficiency of m-Xylene from SKC Lot 2000 Charcoal

         level		sample number
         × OSHA PEL	µg per sample	1	2	3	4	5	6	mean
         RQL	0.548	107.1	104.6	97.9	92.7	95.4	95.7	98.9
         0.05	256	96.9	96.1	95.3	94.7	94.6	95.8	95.6
         0.1	512	96.5	99.7	96.3	94.0	96.7	94.0	96.2
         0.2	1024	96.5	95.2	94.6	96.5	95.6	94.4	95.5
         0.5	2560	97.7	96.0	94.6	93.9	95.0	95.3	95.4
         1.0	5136	97.0	96.5	96.5	97.6	98.1	97.9	97.3
         2.0	10486	93.7	95.6	94.3	97.6	94.5	95.5	95.2
         wet (1.0)	5136	98.0	96.4	97.7	97.4	96.6	97.9	97.3
         The mean EE at concentrations from the RQL to 2 times the PEL (excepting the wet EE) is 96.3%.

         Table 4.8.1.2
         Extraction Efficiency of o-Xylene from SKC Lot 2000 Charcoal

         level		sample number
         × OSHA PEL	µg per sample	1	2	3	4	5	6	mean
         RQL	0.785	99.6	96.9	100.8	88.4	92.8	95.0	95.6
         0.05	257	93.8	93.0	92.4	91.6	91.6	92.7	92.5
         0.1	514	93.5	96.7	93.3	91.2	93.7	91.2	93.3
         0.2	1028	93.6	92.3	91.8	93.6	92.6	91.4	92.6
         0.5	2570	94.9	93.2	92.0	91.3	92.4	92.7	92.8
         1.0	5179	94.6	94.0	94.0	95.1	95.4	95.4	94.8
         2.0	10575	93.2	94.6	93.9	98.5	93.9	94.5	94.8
         wet (1.0)	5179	95.2	93.8	95.1	94.8	93.9	95.1	94.7
         The mean EE at concentrations from the RQL to 2 times the PEL (excepting the wet EE) is 93.8%.

         Table 4.8.1.4
         Extraction Efficiency of Ethylbenzene from SKC Lot 2000 Charcoal

         level		sample number
         × OSHA PEL	µg per sample	1	2	3	4	5	6	mean
         RQL	0.788	102.1	96.9	100.7	103.3	105.6	90.8	99.9
         0.05	256	96.5	95.7	95.0	94.3	94.2	95.3	95.2
         0.1	512	96.1	99.3	95.9	93.7	96.3	93.3	95.8
         0.2	1024	96.2	94.8	94.2	96.1	95.1	94.0	95.1
         0.5	2560	97.3	95.6	94.2	93.6	94.6	94.9	95.0
         1.0	5118	96.6	96.0	96.0	97.2	97.7	97.5	96.8
         2.0	10450	93.2	95.2	93.8	96.9	94.1	95.1	94.7
         wet (1.0)	5118	97.5	95.9	97.3	96.9	96.2	97.5	96.9
         The mean EE at concentrations from the RQL to 2 times the PEL (excepting the wet EE) is 96.1%.

         level		sample number
         × OSHA PEL	µg per sample	1	2	3	4	5	6	mean
         RQL	0.43	96.9	97.1	96.2	100.7	109.1	96.6	99.4
         0.05	260	98.3	97.4	96.6	95.9	95.9	97.1	96.9
         0.1	519	97.8	101.2	97.6	95.4	98.0	95.2	97.5
         0.2	1038	97.9	96.5	95.8	97.9	96.8	95.8	96.8
         0.5	2596	99.0	97.3	95.8	95.1	96.2	96.5	96.7
         1.0	5216	98.2	97.7	99.0	98.8	99.3	99.1	98.7
         2.0	10650	93.0	95.7	93.7	95.3	94.2	95.6	94.6
         wet (1.0)	5216	99.3	97.7	99.0	98.6	97.9	99.3	98.6
         The mean EE at concentrations from the RQL to 2 times the PEL (excepting the wet EE) is 97.2%.

         Table 4.8.1.5
         Stability of m-Xylene Extracted from SKC Lot 2000 Charcoal

         punctured septa replaced			punctured septa retained
         initial EE (%)	EE after one day (%)	difference (%)	initial EE (%)	EE after one day (%)	difference (%)
         97.0	97.4	0.4	97.6	96.1	-1.5
         96.5	97.1	0.6	98.1	96.7	-1.4
         96.5	98.2	1.7	97.9	95.9	-2.0
         >mean			mean
         96.7	97.6	0.9	97.9	96.2	-1.6

         Table 4.8.1.6
         Stability of o-Xylene Extracted from SKC Lot 2000 Charcoal

         punctured septa replaced			punctured septa retained
         initial EE (%)	EE after one day (%)	difference (%)	initial EE (%)	EE after one day (%)	difference (%)
         94.6	95.1	0.5	95.1	93.6	-1.5
         94.0	94.6	0.6	95.4	94.1	-1.3
         94.0	95.8	1.8	95.4	93.2	-2.2
         mean			mean
         94.2	95.2	1.0	95.3	93.6	-1.7

         Table 4.8.1.7
         Stability of p-Xylene Extracted from SKC Lot 2000 Charcoal

         punctured septa replaced			punctured septa retained
         initial EE (%)	EE after one day (%)	difference (%)	initial EE (%)	EE after one day (%)	difference (%)
         96.6	97.0	0.4	97.2	95.6	-1.6
         96.0	96.7	0.7	97.7	96.2	-1.5
         96.0	97.8	1.8	97.5	95.3	-2.2
         mean			mean
         96.2	97.2	1.0	97.5	95.7	-1.8

         Table 4.8.1.8
         Stability of Ethylbenzene Extracted from SKC Lot 2000 Charcoal

         punctured septa replaced			punctured septa retained
         initial EE (%)	EE after one day (%)	difference (%)	initial EE (%)	EE after one day (%)	difference (%)
         98.2	98.6	0.4	98.8	97.2	-1.6
         97.7	98.2	0.5	99.3	97.8	-1.5
         99.0	99.4	0.4	99.1	97.0	-2.1
         mean			mean
         98.3	98.7	0.4	99.1	97.3	-1.7

      2. SKC 575-002 Passive Samplers

         The extraction efficiencies (EE) of the analytes were determined by liquid-spiking 500-mg portions of SKC Anasorb 747 (the sorbent in SKC 575-002 Passive Samplers) with the analytes at levels from the RQL to 2 times the OSHA PEL for each analyte. These samples were stored overnight at ambient temperature, and then extracted with 2 mL of CS₂ (containing 1 µL of 1-phenylhexane per mL of CS₂) for 1 hour. The samples were vigorously shaken periodically over the extraction time. The EEs of the analytes at the target concentration were also determined from "wet" samplers to confirm that EE remained constant. Wet SKC 575-002 Passive Samplers were prepared by sampling from a humid (about 80% RH and 22 °C) atmosphere for 4 hours. These samples were extracted with 2 mL of CS₂ (containing 1 µL of 1-phenylhexane per mL of CS₂) for 1 hour on a SKC 226D-03K Desorption Shaker. The stability of extracted samples was investigated by reanalyzing the 1 × PEL samples a day after the original analysis. Three vials were immediately resealed with new septa caps and three vials retained their punctured septa following the original analysis.

         Table 4.8.2.1
         Extraction Efficiency of m-Xylene from SKC Anasorb 747

         level		sample number
         × OSHA PEL	µg per sample	1	2	3	4	5	6	mean
         RQL	1.422	93.0	90.1	99.0	89.9	105.4	100.9	96.4
         0.05	73	98.6	97.7	97.6	97.2	98.2	97.6	97.8
         0.1	145	95.9	95.9	93.7	95.0	95.8	95.3	95.3
         0.2	290	93.2	93.6	94.2	94.1	94.9	95.6	94.3
         0.5	725	94.1	95.1	95.6	96.3	94.7	97.1	95.5
         1.0	1451	97.2	96.1	101.1	95.8	96.0	97.0	97.2
         2.0	2902	99.3	95.3	96.0	95.8	96.4	95.8	96.4
         wet (1.0)	1498	96.6	96.7	93.8	98.0	96.7	95.3	96.2
         The mean EE at concentrations from the RQL to 2 times the PEL (excepting the wet EE) is 96.1%.

         Table 4.8.2.2
         Extraction Efficiency of o-Xylene from SKC Anasorb 747

         level		sample number
         × OSHA PEL	µg per sample	1	2	3	4	5	6	mean
         RQL	1.075	83.9	76.4	86.3	87.8	86.6	88.1	84.9
         0.05	73	92.3	90.9	91.0	90.4	91.8	91.5	91.3
         0.1	146	89.8	89.6	87.5	89.0	89.9	89.3	89.2
         0.2	292	87.7	88.0	88.4	88.4	89.0	89.8	88.6
         0.5	728	88.4	89.2	89.8	90.4	88.8	91.2	89.6
         1.0	1456	91.5	90.5	95.3	90.1	90.4	91.3	91.5
         2.0	2913	93.7	88.7	90.7	90.5	90.9	90.4	90.8
         wet (1.0)	1511	91.0	90.8	88.3	92.2	91.1	89.9	90.6
         The mean EE at concentrations from the RQL to 2 times the PEL (excepting the wet EE) is 89.4%.

         Table 4.8.2.3
         Extraction Efficiency of p-Xylene from SKC Anasorb 747

         level		sample number
         × OSHA PEL	µg per sample	1	2	3	4	5	6	mean
         RQL	1.542	98.2	95.7	92.2	90.9	97.3	99.3	95.6
         0.05	73	97.6	97.2	96.9	96.0	97.4	96.7	97.0
         0.1	145	95.0	94.8	93.0	94.3	95.1	94.7	94.5
         0.2	290	92.4	92.9	93.4	93.3	94.2	94.7	93.5
         0.5	725	93.3	94.3	94.8	95.4	93.9	96.2	94.7
         1.0	1451	96.3	95.2	100.2	94.9	95.1	96.1	96.3
         2.0	2902	99.7	94.5	95.2	95.0	95.6	94.9	95.8
         wet (1.0)	1493	95.7	95.7	92.9	97.0	95.8	94.4	95.3
         The mean EE at concentrations from the RQL to 2 times the PEL (excepting the wet EE) is 95.3%.

         Table 4.8.2.4
         Extraction Efficiency of Ethylbenzene from SKC Anasorb 747

         level		sample number
         × OSHA PEL	µg per sample	1	2	3	4	5	6	mean
         RQL	1.058	99.7	105.0	93.7	88.5	95.2	103.4	97.6
         0.05	74	102.2	101.2	101.1	100.2	101.2	100.8	101.1
         0.1	147	99.1	99.1	97.3	98.6	99.3	98.6	98.7
         0.2	294	96.3	96.8	97.5	97.2	98.4	98.8	97.5
         0.5	736	97.3	98.4	98.9	99.5	98.3	100.5	98.8
         1.0	1471	100.5	99.3	104.4	99.0	99.1	100.3	100.4
         2.0	2942	102.6	98.3	99.1	98.8	99.6	98.9	99.6
         wet (1.0)	1521	99.8	100.1	97.0	101.3	100.0	98.4	99.4
         The mean EE at concentrations from the RQL to 2 times the PEL (excepting the wet EE) is 99.1%.

         Table 4.8.2.5
         Stability of m-Xylene Extracted from SKC Anasorb 747

         punctured septa replaced			punctured septa retained
         initial EE (%)	EE after one day (%)	difference (%)	initial EE (%)	EE after one day (%)	difference (%)
         97.2	97.8	0.6	95.8	94.2	-1.6
         96.1	95.4	-0.7	96.0	94.0	-2.0
         101.1	100.0	-1.1	97.0	95.7	-1.3
         mean			mean
         98.1	97.7	-0.4	96.3	94.6	-1.6

         Table 4.8.2.6
         Stability of o-Xylene Extracted from SKC Anasorb 747

         punctured septa replaced			punctured septa retained
         initial EE (%)	EE after one day (%)	difference (%)	initial EE (%)	EE after one day (%)	difference (%)
         91.5	91.9	0.4	90.1	88.8	-1.3
         90.5	89.7	-0.8	90.4	88.7	-1.7
         95.3	94.2	-1.1	91.3	90.2	-1.1
         mean			mean
         92.4	91.9	-0.5	90.6	89.2	-1.4

         Table 4.8.2.7
         Stability of p-Xylene Extracted from SKC Anasorb 747

         punctured septa replaced			punctured septa retained
         initial EE (%)	EE after one day (%)	difference (%)	initial EE (%)	EE after one day (%)	difference (%)
         96.3	96.9	0.6	94.9	93.5	-1.4
         95.2	94.6	-0.6	95.1	93.3	-1.8
         100.2	99.3	-0.9	96.1	94.9	-1.2
         mean			mean
         97.2	96.9	-0.3	95.4	93.9	-1.5

         Table 4.8.2.8
         Stability of Ethylbenzene Extracted from SKC Anasorb 747

         punctured septa replaced			punctured septa retained
         initial EE (%)	EE after one day (%)	difference (%)	initial EE (%)	EE after one day (%)	difference (%)
         100.5	101.0	0.5	99.0	97.3	-1.7
         99.3	98.7	-0.6	99.1	97.1	-2.0
         104.4	103.4	-1.0	100.3	98.8	-1.5
         mean			mean
         101.4	101.0	-0.4	99.5	97.7	-1.7

   9. Interferences (sampling)
      1. Charcoal tubes

         Retention

         The ability of charcoal tubes to retain mixed xylenes after collection was tested by sampling a test atmosphere containing 454 mg/m³, 211 mg/m³, 198 mg/m³, and 161 mg/m³ m-xylene, o-xylene, p-xylene, and ethylbenzene, respectively (at 80% RH and 20 °C) with six samplers for one hour at 50 mL/min. Three samples were analyzed immediately and three were used to sample contaminant-free humid air for an additional three hours, and then analyzed. All the samples in the second set retained at least 101.0, 101.2, 100.8, 101.0% of the means of the first set for m-xylene, o-xylene, p-xylene, and ethylbenzene, respectively.

         Table 4.9.1
         Retention of Mixed Xylenes on Charcoal Tubes

         	m-xylene		o-xylene		p-xylene		ethylbenzene
         	(mg/m3)	(% mean)	(mg/m3)	(% mean)	(mg/m3)	(% mean)	(mg/m3)	(% mean)
         1st set 1 2 3 mean 2nd set 1 2 3	443.9 428.5 447.4 439.9   444.3 453.4 449.5	101.0 103.1 102.2	203.9 194.6 206.1 201.5   203.9 208.3 207.2	101.2 103.4 102.8	192.6 185.7 194.1 190.8   192.4 196.7 195.0	100.8 103.1 102.2	158.6 154.8 159.5 157.6   159.2 161.9 159.5	101.0 102.7 101.2

         Low relative humidity

         The ability of charcoal tubes to collect mixed xylenes at low humidity was tested by sampling a test atmosphere containing 468 mg/m³, 218 mg/m³, 204 mg/m³, 166 mg/m³ m-xylene, o-xylene, p-xylene, and ethylbenzene, respectively (at 5% RH and 20 °C) with three samplers for four hours at 50 mL/min. The samples were analyzed immediately. The sample results (when compared to theoretical concentrations) were 102.0, 100.4, and 99.8% for m-xylene; 101.4, 100.4, and 99.2% for o-xylene; 101.6, 100.1, and 99.6% for p-xylene; and 102.5, 100.8, and 100.4% for ethylbenzene.

         Low concentration

         The ability of charcoal tubes to collect mixed xylenes at low concentrations was tested by sampling a test atmosphere containing 22 mg/m³, 10 mg/m³, 10 mg/m³, 8 mg/m³ m-xylene, o-xylene, p-xylene, and ethylbenzene, respectively (at 80% RH and 22 °C) with three samplers for four hours at 50 mL/min. The samples were analyzed immediately. The sample results (when compared to theoretical concentrations) were 95.2, 97.6, and 102.2 for m-xylene; 94.6, 96.1, and 101.2% for o-xylene; 95.0, 97.2, and 101.8% for p-xylene; and 96.1, 98.6, and 102.5% for ethylbenzene.

         Interference

         The ability of charcoal tubes to collect mixed xylenes in the presence of sampling interferences was tested by sampling a test atmosphere containing 230 mg/m³, 107 mg/m³, 100 mg/m³, 82 mg/m³, 365 mg/m³, 372 mg/m³ m-xylene, o-xylene, p-xylene, ethylbenzene, toluene, and butyl acetate respectively (at 81% RH and 21 °C) with three samplers for four hours at 50 mL/min. The samples were analyzed immediately. The sample results (when compared to theoretical concentrations) were 103.3, 102.9, and 101.8 for m-xylene; 102.8, 102.5, and 101.2% for o-xylene; 103.2, 102.6, and 101.6% for p-xylene; and 104.1, 103.4, and 102.6% for ethylbenzene.

      2. SKC 575-002 Passive Samplers

         Reverse diffusion

         The ability of SKC 575-002 Passive Samplers to retain mixed xylenes after collection was tested by sampling a test atmosphere containing 454 mg/m³, 211 mg/m³, 198 mg/m³, and 161 mg/m³ m-xylene, o-xylene, p-xylene, and ethylbenzene, respectively (at 80% RH and 20 °C) with six samplers for one hour. Three samples were analyzed immediately and three were used to sample contaminant-free humid air for an additional three hours, and then analyzed. Sampling rates from Section 4.7 were converted to their equivalents under experimental temperature and pressure and used to calculate results in Table 4.9.2. All the samples in the second set retained at least 100.2, 99.6, 99.8, and 100.0% of the means of the first set for m-xylene, o-xylene, p-xylene, and ethylbenzene, respectively.

         Table 4.9.2
         Retention of Mixed Xylenes on SKC 575-002 Passive Samplers

         	m-xylene		o-xylene		p-xylene		ethylbenzene
         	(mg/m3)	(% mean)	(mg/m3)	(% mean)	(mg/m3)	(% mean)	(mg/m3)	(% mean)
         1st set 1 2 3 mean 2nd set 1 2 3	450.6 449.4 419.5 439.8   440.7 449.0 449.4	100.2 102.1 102.2	206.9 208.0 191.9 202.3   201.4 206.0 205.9	99.6 101.8 101.8	195.7 197.0 182.0 191.6   191.2 195.0 195.3	99.8 101.8 101.9	161.2 162.8 149.9 158.0   157.9 160.8 161.4	100.0 101.8 102.2

         Low relative humidity

         The ability of SKC 575-002 Passive Samplers to collect mixed xylenes at low humidity was tested by sampling a test atmosphere containing 468 mg/m³, 218 mg/m³, 204 mg/m³, 166 mg/m³ m-xylene, o-xylene, p-xylene, and ethylbenzene, respectively (at 5% RH and 20 °C) with three samplers for four hours. The samples were analyzed immediately. Sampling rates (760 mmHg and 25 °C) were 13.92, 13.63, and 13.94 mL/min for m-xylene; 14.23, 13.93, and 14.24 mL/min for o-xylene; 14.05, 13.77, and 14.08 mL/min for p-xylene; and 14.01, 13.73, and 14.02 mL/min for ethylbenzene.

         Low concentration

         The ability of SKC 575-002 Passive Samplers to collect mixed xylenes at low concentrations was tested by sampling a test atmosphere containing 22 mg/m³, 10 mg/m³, 10 mg/m³, 8 mg/m³ m-xylene, o-xylene, p-xylene, and ethylbenzene, respectively (at 80% RH and 22 °C) with three samplers for four hours. The samples were analyzed immediately. Sampling rates (760 mmHg and 25 °C) were 13.44, 13.68, and 13.16 mL/min for m-xylene; 13.90, 14.28, and 13.53 mL/min for o-xylene; 13.32, 13.69, and 13.36 mL/min for p-xylene; and 13.71, 13.76, and 13.37 mL/min for ethylbenzene.

         Interference

         The ability of SKC 575-002 Passive Samplers to collect mixed xylenes in the presence of sampling interferences was tested by sampling a test atmosphere containing 230 mg/m³, 107 mg/m³, 100 mg/m³, 82 mg/m³, 365 mg/m³, 372 mg/m³ m-xylene, o-xylene, p-xylene, ethylbenzene, toluene, and butyl acetate respectively (at 81% RH and 21 °C) with three samplers for four hours. The samples were analyzed immediately. Sampling rates (760 mmHg and 25 °C) were 13.73, 13.12, and13.77 mL/min for m-xylene; 14.06, 13.43, and 14.08 mL/min for o-xylene; 13.86, 13.25, and 13.90 mL/min for p-xylene; and 13.80, 13.18, and 13.86 mL/min for ethylbenzene.

   10. Qualitative analysis

       The identity of suspected mixed xylenes can be confirmed by GC/mass spectrometry. Mass spectra for the analytes are presented below.

       

       Figure 4.10.1 Mass spectrum for m-xylene.

       

       Figure 4.10.2 Mass spectrum for o-xylene.

       

       Figure 4.10.3 Mass spectrum for p-xylene.

       

       Figure 4.10.4 Mass spectrum for ethylbenzene.

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