METHYL ACETATE: METHOD 1458, Issue 2, dated 15 August 1994 - Page 3 of 3 b.
10.
Inject a known amount of analyte or of a standard solution of analyte in CS 2 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. µg analyte recovered. Analyze three quality control blind spikes and three analyst spikes to insure that the calibration graph and DE graph are in control.
MEASUREMENT: 11.
12.
Set gas chromatograph according to manufacturer's recommendations to conditions given on page 1458-1. 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, reanalyze, and apply appropriate dilution factor in calculations. Measure peak area.
CALCULATIONS: 13.
14.
Determine the mass, µg (corrected for DE), of methyl acetate 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. Calculate concentration, C, of analyte in the air volume sampled, V (L):
EVALUATION OF METHOD: This method was validated over the range 343 to 1330 mg/m 3 at 24 °C and 761 mm Hg using 7-liter samples [1]. Breakthrough capacity was 14 mg when sampling dry air containing 1330 mg/m 3. Overall sampling and measurement precision, SˆrT, was 0.0547. Desorption efficiency (DE) of methyl acetate from charcoal tubes was 85.7% in the range of 87 to 342 µg per sample [2]. Sample storage stability was evaluated at 203 µg per sample [2]. Samples stored at ambient temperature in the dark had a 91.8% recovery after three days when compared to day 1 samples. Samples stored at 5 °C gave recoveries of 96.4% on day 6 and 90.4% on day 9. Therefore, methyl acetate is stable on charcoal for at least 6 days and up to 9 days, when refrigerated at 5 °C.
REFERENCES: [1] [2] [3] [4]
NIOSH Manual of Analytical Methods, 2nd ed., Vol. 2, S42, U.S. Dept. of Health, Education, and Welfare, Publ. (NIOSH) 77-157B (1977). Pendergrass, S.M., Methyl Acetate Method Development (Unpublished report), NIOSH/MRSB, 1990. Analysis of NIOSH Samples for Methyl Acetate, NIOSH/MRSB/MDS, Sequence #7034, Cincinnati, Ohio (unpublished, 1990). Beck, S, T. Stock, and L. Whitehead, Improved Efficiency of Desorption of Oxygenated Solvents from Activated Charcoal Using a New Polar Additive to Carbon Disulfide, Appl. Occup. Environ . Hyg. 5(3), 171-177, 1990.
METHOD REVISED BY: S.M. Pendergrass, NIOSH/DPSE NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94
