METHYL IODIDE: METHOD 1014, Issue 2, dated 15 August 1994 - Page 3 of 4 a. b.
10.
Remove and discard back sorbent section of a media blank sampler. Inject a known amount (1 to 20 µL) of calibration stock solution or a dilution thereof 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 methyl iodide recovered. Analyze three quality control blind spikes or three analyst spikes to ensure that the calibration graph and DE graph are in control.
MEASUREMENT: 11.
12.
Set gas chromatograph operating parameters according to manufacturer's recommendations and those given on page 1014-1. 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 toluene, reanalyze, and apply the appropriate dilution factor in calculations. Measure peak area.
CALCULATIONS: 13.
14.
Determine the mass, mg (corrected for DE) of analyte 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 the concentration, C, of analyte in the air volume sampled, V (L):
EVALUATION OF METHOD: Method S98 was issued on April 11, 1975 [3] and evaluated using atmospheres containing methyl iodide generated in dry air [1]. The samples were analyzed by gas chromatography along with spiked samplers to correct for desorption efficiency (DE) which was determined to be 0.85, 0.91 and 0.92 at 0.7, 1.4 and 2.8 mg methyl iodide, respectively, from 100 mg of SKC Lot 105 activated coconut shell charcoal. Long-term stability of methyl iodide on the charcoal has not been investigated. When an atmosphere containing 52 mg/m 3 methyl iodide in dry air was sampled at a rate of 1 L/min for 4 hrs, the concentration of methyl iodide in the effluent was 2% of that in the influent, indicating near breakthrough. Therefore, the adsorptive capacity of this lot of charcoal is approximately 12.5 mg methyl iodide, and the breakthrough volume is approximately 240 L under the conditions investigated.
REFERENCES: [1]
[2] [3] [4]
Documentation of the NIOSH Validation Tests, S98, 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. UBTL, Inc., NIOSH Sequence #3428-M (unpublished, April 21, 1982). NIOSH Manual of Analytical Methods, 2nd ed., Vol. 2, S98, U.S. Department of Health, Education, and Welfare, Publ. (NIOSH) 77-157-B (1977). NIOSH Current Intelligence Bulletin 43, Monohalomethanes, U.S. Department of Health and Human Services, Publ. (NIOSH) 84-117 (1984).
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94
