TETRAETHYL PYROPHOSPHATE: METHOD 2504, Issue 2, dated 15 August 1994 - Page 3 of 4 9.
10.
Determine desorption efficiency (DE) at least once for each batch of Chromosorb 102 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 calibration stock solution 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 TEPP 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 2504-1. 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 eluent, reanalyze and apply the appropriate dilution factor in calculations. Measure peak area. Divide the peak area of analyte by the peak area of internal standard on the same chromatogram.
CALCULATIONS: 13.
14.
Determine the mass, µg (corrected for DE) of TEPP 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 TEPP in the air volume sampled, V (L):
EVALUATION OF METHOD: Method P&CAM 336 [2] was evaluated over the range 0.025 to 0.102 mg/m 3 at 21.5 °C and 735.3 mm Hg using 48-L samples [1,4]. Overall precision, SˆrT, was 0.086 with an average recovery of 99.4%, representing a non-significant bias. The concentration of TEPP was independently verified by sampling the generator with toluene-filled bubblers and analysis by GC/FPD. Desorption efficiency averaged 0.994 in the range 1.1 µg to 4.8 µg per sample. After sampling an atmosphere containing 0.41 µg/m 3 at 0.18 L/min at 90% RH for 300 min, only 0.2% of the influent concentration was detected breaking through the sorbent bed.
REFERENCES: [1] [2] [3]
Backup Data Report S305, TEPP, prepared under NIOSH Contract No. 210-76-0123 (August, 1979). NIOSH Manual of Analytical Methods, 2nd ed., V. 6, P&CAM 336, U.S. Department of Health and Human Services, Publ. (NIOSH) 80-125 (1980). Criteria for a Recommended Standard...Occupational Exposure During the Manufacture and Formulation of Pesticides, U.S. Department of Health, Education, and Welfare, Publ. (NIOSH) 78-174 (1978). NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94
