Page:NIOSH Manual of Analytical Methods - 1001.pdf/3

 METHYL CHLORIDE: METHOD 1001, Issue 2, dated 15 August 1994 - Page 3 of 4 7.

Place, in order, the back and front sorbent sections of the back sampler tube into a second bottle, discarding the glass wool and foam plugs. Immediately cap and gently shake the bottle. Analyze within 6 h.

CALIBRATION AND QUALITY CONTROL: 8.

9.

Calibrate daily with at least six working standards. a. Pipet 3.0 mL CH 2Cl2 into each of a series of bottles. Cap the bottles. b. Using a gas-tight syringe, add known amounts of methyl chloride (0.005 to 0.5 mL; 0.01 to 1 mg at NTP) by bubbling the gas slowly through the CH 2Cl2. Gently shake the bottles. c. Analyze with samples and blanks (steps 10 and 11). d. Prepare calibration graph (peak area vs. mg methyl chloride). Determine desorption efficiency (DE) at least once for each lot of sorbent used for sampling in the range of interest. Prepare three tubes at each of five levels plus three media blanks. a. Using a gas-tight syringe, slowly inject a known amount of methyl chloride (0.005 to 0.5 mL) through the septum of the DE apparatus into a stream of nitrogen which carries the analyte into a large (400 mg/200 mg) sorbent tube. Allow the nitrogen to flow an additional 1 min. b. Cap the tube. Allow to stand overnight. c. Desorb (steps 5 through 7) and analyze with working standards (steps 10 and 11). d. Prepare a graph of DE vs. mg methyl chloride recovered.

MEASUREMENT: 10.

11.

Set gas chromatograph according to manufacturer's recommendations and to conditions given on page 1001-1. Inject sample aliquot manually using solvent flush technique or with autosampler. NOTE: If peak area is above the linear range of the working standards, dilute an aliquot of the desorbed liquid with CH 2Cl2, reanalyze and apply the appropriate dilution factor in calculations. Measure peak area. NOTE: Methyl chloride elutes before CH 2Cl2 under these conditions.

CALCULATIONS: 12.

13.

Determine the mass, mg (corrected for DE) of methyl chloride found in the sample front (W f) and back (W b) sorbent sections, and in the average media blank front (B f) and back (B b) sorbent sections. NOTE: If W b > W f/10, report breakthrough and possible sample loss. Calculate concentration, C, of methyl chloride in the air volume sample, V (L):

EVALUATION OF METHOD: Method S99 was issued on March 18, 1977 [3], and validated with generated atmospheres monitored by total hydrocarbon analyzer [1,8]. Average recovery was 105% with Sr = 0.05 for eighteen 1.5-L samples in the range 110 to 460 mg/m 3 and 101% with Sr = 0.05 for eighteen 0.5-L samples in the range 300 to 1200 mg/m 3. Breakthrough (effluent = 5% of test concentration) occurred after sampling for 135 min at 0.0235 L/min from an atmosphere containing 410 mg/m 3 methyl chloride in air at 80% RH, and at 24.4 NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94