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Related Information: Chemical Sampling - 2-Nitropropane
Organic Methods Evaluation Branch
OSHA Analytical Laboratory
Salt Lake City, Utah
1. General Discussion
A number of early analytical procedures for nitro paraffins are reported in the literature (Ref. 5.1.). The only procedure found which is directed towards industrial hygiene application is a colorimetric procedure in which the samples are collected in concentrated sulfuric acid (Ref. 5.2.). The
The most common procedure for determining air concentrations of solvent vapors is collection of the vapors with charcoal adsorbent tubes and analysis by GC after desorption with carbon disulfide. When this procedure is used to determine
1.1.2. Toxic effects (This section is for information only and should not be taken as the basis of OSHA policy.)
Exposure to concentrations of
1.1.3. Work population
An estimated 100,000 workers are potentially exposed to
1.1.4. Use and operations where exposure occur
The following information is taken directly from Reference 5.8.
1.1.5. Physical properties (Refs. 5.9. and 5.10.)
1.2. Detection limit, precision, sensitivity and working range
1.2.2. The pooled coefficient of variation of the analytical procedure over the range of 3.95 to 395 µg per sample is 0.023. (Section 4.2.) This represents an air concentration range of 0.54 to 54 ppm based on the recommended sampling and analytical procedures.
1.2.3. The sensitivity of the analytical procedure over a concentration range representing 0.02 to 2 times the target concentration based on the recommended air volume is 916.6 area units per µg/mL. The sensitivity is determined by the slope of the calibration curve (Section 4.2.) The sensitivity will vary somewhat with the particular instrumentation used in the analysis.
1.2.4. The lower limit of the estimated working range, assuming adequate desorption efficiency, is 0.27 ppm. The upper limit of the working range is dependent on the capacity of the collection medium.
1.3.2. The recovery of analyte from the collection medium after storage must be 75% or greater.
1.3.3. The overall procedure has met the above validation criteria. (Section 4.3.)
1.4.2. The analytical procedure is quick, sensitive, and reproducible.
If other compounds are present, the GC run time must be lengthened so the late eluters will not interfere with the next sample.
2. Sampling Procedure
2.1.2. Chromosorb 106 tubes: Glass tube with both ends heat sealed, 7 cm × 6-mm o.d. × 4-mm i.d., containing 100-mg front and 50-mg backup sections of Chromosorb 106 (60/80 mesh). SKC tubes or equivalent.
2.1.3. The Chromosorb 106 tubes are conditioned prior to use by heating overnight in a GC oven at 120°C with a carrier gas of helium or nitrogen flowing through the tubes. Conditioning removes residual components from the Chromosorb 106 which may interfere with the analysis.
2.3. Sampling technique
2.3.2. Connect the Chromosorb 106 tube to the sampling pump with flexible tubing. The short section of the Chromosorb 106 tube is used as a backup and should be positioned nearer the sampling pump.
2.3.3. The tube should be placed in a vertical position during sampling to minimize channeling.
2.3.4. Air being sampled should not pass through any hose or tubing before entering the Chromosorb 106 tube.
2.3.5. Seal the Chromosorb 106 tube with plastic caps immediately after sampling. Also, seal each sample with OSHA sealing tape lengthwise.
2.3.6. With each batch of samples, submit at least one blank tube from the same lot used for samples. This tube should be subjected to exactly the same handling as the samples (open, seal, transport) except that no air is drawn through it.
2.3.7. Transport the samples (and corresponding paperwork) to the lab for analysis.
2.3.8. If bulk samples are submitted for analysis, they should be transported in glass containers with Teflon-lined caps. These samples must not be put in the same container used for the Chromosorb 106 tubes.
Breakthrough tests were performed with the primary section of Chromosorb 106 tubes using a controlled test atmosphere containing 52 ppm
2.5. Desorption efficiency
The desorption efficiency from liquid injections on Chromosorb 106 tubes averaged 99.3% for 99 to 395 µg per tube, which is 13.6 to 54 ppm for a 2-L air volume. (Section 4.4.)
2.6. Recommended air volume and sampling rate
2.6.2. The recommended sampling rate is 0.2 L/min.
2.6.3. If a longer sampling time is required, a sampling rate of 0.05 L/min to 0.1 L/min can be used.
2.7. Interferences (sampling)
2.7.2. Any compound which is suspected of interfering in the collection or analysis should be listed on the sampling data sheet.
2.8. Safety precautions
2.8.2. When working in environments containing flammable vapors, do not provide any spark source from equipment used or pumps.
2.8.3. Observe all safety practices for working in hazardous areas.
3. Analytical Procedure
3.1.2. A number of GC columns are available and adequate. The column used for this study was a 1/8-in. × 10-ft, stainless steel, 7% Tetracyanoethylated Pentaerythritol on 100/120 mesh Chromosorb P-AW.
3.1.3. An electronic integrator or other suitable method of measuring peak areas.
3.1.4. Two-milliliter vials with Teflon-lined caps.
3.1.5. Microliter syringes, 10-µL for preparing standards, 1-µL for sample injections.
3.1.6. Pipets for diluting standards. A 1.0-mL pipet for dispensing solvent for desorption, or a 1.0-mL repipet dispenser.
3.1.7. Volumetric flasks, convenient sizes for preparing standards.
3.2.3. Purified GC grade helium, hydrogen, and air.
3.3. Standard preparation
3.3.2. Five microliters of
3.4. Sample preparation
3.4.2. Each section is desorbed with 1.0 mL of ethyl acetate.
3.4.3. The vials are sealed immediately and allowed to desorb for 30 min with intermittent shaking.
A typical chromatogram of
3.5.3. Peak areas are measured by an electronic integrator or other suitable means.
3.5.4. An external standard procedure is used. The integrator is calibrated to report results in ppm for a 2-L air sample after correction for desorption efficiency.
3.6. Interferences (analytical)
3.6.2. GC parameters may be changed to circumvent most interferences.
3.6.3. Retention time on a single column is not considered proof of chemical identity. Samples should be confirmed by GC/MS or other suitable means.
Usually the integrator is programmed to report for a 2-L air sample. The following calculation is used:
3.8. Safety precautions
3.8.2. Avoid any skin contact with all of the solvents.
3.8.3. Safety glasses should be worn throughout the procedure.
4. Backup Data
A small amount of analyte (1.98 ng/injection) which produced a well defined peak was designated as the analytical detection limit. This was determined with an analytical standard which contained 0.002 µL of
Reproducibility of the peak produced by 1.98 ng was good. Eight injections resulted in a coefficient of variation of 5.5%.
A sample collected from 2 L of air which contained 1.98 ng/µL after desorption with 1 mL of ethyl acetate would represent an air concentration of 0.27 ppm.
4.2. Precision data
Multiple injections were made of the standards that were prepared over a range of 0.02 to 2.2 times the target concentration. A standard deviation and a coefficient of variation was determined at each concentration. The pooled coefficient of variation was determined for the range.
4.3. Storage data
Samples were collected on Chromosorb 106 from a generated atmosphere containing 25.3 ppm
4.4. Desorption efficiency
Liquid injections were made on the front section of conditioned Chromosorb 106 tubes at approximately 0.5, 1, and 2 times the target concentration. These were refrigerated overnight, desorbed and analyzed the following day. The overall desorption for the concentration studied is 99.3%.
Figure 3.5.2. Chromatogram of a standard of
Figure 4.2. Calibration curve of instrument response to
Figure 4.3.1. Ambient storage test of
Figure 4.3.2. Refrigerated storage test of
5.2. Jones, L. R., American Industrial Hygiene Association Journal, 24, 11-16, 1963.
5.3. Taylor, D. G. (Manual Coordinator) "NIOSH Manual of Analytical Methods". 2nd Edition, U.S. DHEW/PHS/CDC/NIOSH, Vol. 4, Method No. P&CAM 272, 1978.
5.4. Skinner, J. B., Ind. Med., 16, 441, 1974.
5.5. "Documentation of Threshold Limit Values", American Conference of Governmental Industrial Hygienists, 3rd Ed., p. 188-189, 1971.
5.6. Freon and Dutra Arch. Ind. Hyg. and Occ. Med., 5, 52, 1952.
5.7. Gaultier, M., et.al., Arch. I. Mal. Prof., 25, 425, 1964.
5.8. U.S. DHEW/PHS/CDC/NIOSH "Current Intelligence Bulletin 17" DHEW (NIOSH), April 25, 1977.
5.9. Patty, F. A. (Ed.) "Industrial Hygiene and Toxicology", 2nd ed., New York: John Wiley and Sons, Inc., p. 2073, 1963.
5.10. Standen, A. (Ed.), "Kirk-Othmer Encyclopedia of Chemical Technology". 2nd ed., New York: Interscience Publishers, Vol. 13, p. 866, 1964.