TETRAHYDROFURAN: METHOD 1609, Issue 2, dated 15 August 1994 - Page 3 of 3 a. b.
10.
Remove and discard back sorbent section of a media blank sampler. Inject a known amount (1 to 20 µL) of THF or a standard solution of THF 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. mg THF 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 1609-1. 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 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 THF 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 THF in the air volume sampled, V (L):
EVALUATION OF METHOD: Method S78 was issued on February 14, 1975 [3]. The precision and bias were determined by analyzing generated atmospheres of tetrahydrofuran in dry air containing 323, 636 and 1240 mg/m 3 at 22.5 °C and 763 mm Hg using 9-L samples [1]. The concentrations were determined by comparison with a "bag" standard using a hydrocarbon analyzer. Storage stability was not assessed. Breakthrough of the front section of the charcoal tube was observed after sampling 13.32 L of dry test atmosphere containing 1140 mg/m 3 for 72 min at 0.185 L/min. Desorption efficiencies for samples spiked with tetrahydrofuran were 0.91 to 0.95 in the range 3 to 11.8 mg tetrahydrofuran per sample. REFERENCES: [1]
[2] [3] [4]
Documentation of the NIOSH Validation Tests, S78, 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. User check, UBTL, Inc., NIOSH Sequence #4585-S (NIOSH, unpublished, March 21, 1985). NIOSH Manual of Analytical Methods, 2nd ed., Vol. 2, S78, U.S. Department of Health, Education, and Welfare, Publ. (NIOSH) 77-157-B (1977). NIOSH/OSHA Occupational Health Guidelines for Chemical Hazards, U.S. Department of Health, Education, and Welfare, Publ. (NIOSH) 81-123 (1981), available as GPO Stock
- 017-033-0037-8 from Superintendent of Documents, Washington, DC 20402.
METHOD REVISED BY: Julie R. Okenfuss, NIOSH/DPSE; S78 originally validated under NIOSH Contract CDC-99-74-45.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94
