ETHYL BROMIDE: METHOD 1011, Issue 2, dated 15 August 1994 - Page 3 of 4
9.
10.
b. Analyze together with samples and blanks (steps 11 and 12). c. Prepare calibration graph (peak area vs. mg ethyl bromide). Determine desorption efficiency (DE) at least once for each lot of charcoal used for sampling in the calibration range (step 8). Prepare three tubes at each of five levels plus three media blanks. a. Remove and discard back sorbent section of a media blank sampler. b. Inject a known amount (1 to 20 µL) of ethyl bromide or calibration stock solution directly onto front sorbent section with a microliter syringe. c. Cap the tube. Allow to stand overnight. d. Desorb (steps 5 through 7) and analyze together with working standards (steps 11 and 12). e. Prepare a graph of DE vs. mg ethyl bromide recovered. Analyze three quality control blind spikes and three analyst spikes to ensure that the calibration graph and DE graph are in control.
MEASUREMENT: 11.
12.
Set gas chromatograph according to manufacturer's recommendations and to conditions given on page 1011-1. 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 with 2-propanol, reanalyze, and apply the appropriate dilution factor in calculations. Measure peak area.
CALCULATIONS: 13.
14.
Determine the mass, mg (corrected for DE) of ethyl bromide 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 ethyl bromide in the air volume sampled, V (L):
EVALUATION OF METHOD: Method S106 was issued on April 11, 1975 [3], and validated over the range 550 to 2200 mg/m 3 using 4-L air samples [1]. The concentrations of ethyl bromide were independently determined by gas chromatographic analysis of the synthetic atmospheres using a 5-mL sampling loop. The average recovery of generated samples was 93.8% with a relative standard deviation of 6.3%. No storage stability study was done. The breakthrough volume was 6.4 L when dry air containing 2213 mg/m 3 of ethyl bromide was sampled at 0.2 L/min. Desorption efficiencies averaged 0.84 over the range 1.8 to 7.1 mg per sample. At 0.03 mg per sample, a desorption efficiency of 0.63 was found [2].
REFERENCES: [1] Documentation of the NIOSH Validation Tests, U.S. Department of Health, Education, and Welfare, Publ. (NIOSH) 77-185 (1977), available as GPO Stock #017-033-00231-2 from Superintendent of Documents, Washington, DC 20402. [2] User check, UBTL, Inc., NIOSH Sequence #4585-K (NIOSH, unpublished, October 31, 1984). [3] NIOSH Manual of Analytical Methods, 2nd ed., Vol. 2, S106, U.S. Department of Health, Education, and Welfare, Publ. (NIOSH) 77-157-B (1977). NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94
