1,1,2,2-TETRACHLOROETHANE: METHOD 1019, Issue 2, dated 15 August 1994 - Page 3 of 4 9.
10.
Determine desorption efficiency (DE) at least once for each lot of sorbent used for sampling in the range of interest. Prepare three tubes at each of five concentrations plus three media blanks. a. Remove and discard back sorbent section of a media blank sampler. b. Inject a known amount (2 to 20 µL) of DE stock solution, or a serial 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 with working standards (steps 11 and 12). e. Prepare a graph of DE vs. mg 1,1,2,2-tetrachloroethane 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 1019-1. 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 1,1,2,2-tetrachloroethane 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 1,1,2,2-tetrachloroethane in the air volume sampled, V (L):
EVALUATION OF METHOD: Method S124 was issued on May 9, 1975 [3], and validated with generated atmospheres which were calibrated by gas chromatography [1]. Average recovery was 106% at 5 ppm. Breakthrough did not occur after sampling 4 h at 0.185 L/min from an atmosphere containing 101 mg/m 3 in dry air. Desorption efficiency for SKC Lot 104 petroleum-based charcoal was 0.83, 0.87, and 0.88 at 0.16, 0.32, and 0.64 mg 1,1,2,2-tetrachloroethane per sample, respectively. Lower recoveries were observed for coconut shell charcoal (SKC Lot 105). In subsequent work, 1,1,2,2-tetrachloroethane was observed to degrade rapidly into trichloroethylene during storage on Pittsburgh activated carbon; 19% converted during one day and 63% converted during eight days at ambient conditions [7]. Therefore, the analyte is sensitive to the sorbent type; only the recommended sorbent should be used. Breakthrough at high relative humidity was not tested, nor was sample stability.
REFERENCES: [1] Documentation of the NIOSH Validation Tests, S124, U.S. Department of Health, Education, and Welfare, Publ. (NIOSH) 77-185 (1977), available as Stock No. PB 274-248 from NTIS, Springfield, VA 22161. [2] UBTL Report for Sequence 1977 (NIOSH, unpublished, September 7, 1979). NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94
