ISOPHORONE: METHOD 2508, Issue 2, dated 15 August 1994 - Page 3 of 3 9.
10.
Determine desorption efficiency (DE) at least once for each batch 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 of isophorone 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 isophorone 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 and to conditions given on page 2508-1. 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 CS 2, reanalyze and apply the appropriate dilution factor in calculations. Measure peak area.
CALCULATIONS: 13.
14.
Determine the mass, mg (corrected for DE) of isophorone 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 isophorone in the air volume sampled, V (L):
EVALUATION OF METHOD: Method S367 [2] was validated over the range 69 to 304 mg/m 3 using a 12-L sample [1]. Overall precision, SˆrT, was 0.059 with an average recovery of 104.9%, representing a non-significant bias. The concentration was independently verified by a direct hydrocarbon analyzer. Desorption efficiency was 0.860 in the range of 0.849 to 3.40 mg per sample. No breakthrough occurred when an atmosphere containing 283 mg/m 3 was sampled for 240 min at a rate of 0.19 L/min. At this time the breakthrough test was discontinued. Samples are stable for at least one week at room temperature.
REFERENCES: [1] Documentation of the NIOSH Validation Tests, S367-1 to S367-6, U.S. Department of Health and Human Services, Publ. (NIOSH) 77-185 (1977). [2] NIOSH Manual of Analytical Methods, 2nd. ed., V. 3, S367, U.S. Department of Health, Education, and Welfare, Publ. (NIOSH) 77-157-C (1977). [3] Criteria for a Recommended Standard...Occupational Exposure to Ketones, U.S. Department of Health, Education, and Welfare, Publ. (NIOSH) 78-173 (1978).
METHOD REVISED BY: Ardith Grote, NIOSH/DPSE; S367 originally validated under NIOSH Contract CDC-99-74-45. NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94
