Page:NIOSH Manual of Analytical Methods - 5514.pdf/3

DEMETON: METHOD 5514, Issue 2, dated 15 August 1994 - Page 3 of 4 CALIBRATION AND QUALITY CONTROL: 9.

10.

11.

Calibrate daily with at least six working standards over the range 0.1 to 100 µg Demeton per sample for each isomer. a. Add known amounts of calibration stock solution to toluene in 10-mL volumetric flasks and dilute to the mark. b. Analyze together with samples and blanks (steps 12 and 13). c. Prepare calibration graph (peak area vs. µg of each isomer). Determine desorption efficiency (DE) at least once for each lot of XAD-2 used for sampling in the calibration range (step 9). 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 (1 to 20 µL) of calibration 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 6 through 8) and analyze together with working standards (steps 12 and 13). e. Prepare a graph of DE vs. µg of each Demeton isomer recovered. Analyze three quality control blind spikes and three analyst spikes to ensure that the calibration graph and DE graph are in control.

MEASUREMENT: 12.

13.

Set gas chromatograph according to manufacturer's recommendations and to conditions given on page 5514-1. Inject sample aliquot manually using solvent flush technique or with autosampler. t r = 4 min for Demeton O and 7.5 min for Demeton S under these conditions. NOTE: If peak area is above the linear range of the working standards, dilute with toluene, reanalyze, and apply the appropriate dilution factor in calculations. Measure peak area.

CALCULATIONS: 14.

15.

Determine the mass, µg (corrected for DE) of Demeton (sum of Demeton O and Demeton S) found on the sample filter plus front sorbent section (W + W f), back (W b) sorbent section, and on the average media blank filter (B) and front (B f) and back (B b) media blank sorbent sections. Calculate concentration, C, of Demeton in the air volume sampled, V (L):

EVALUATION OF METHOD: Method S280 for Demeton was issued on August 3, 1979 [2], and validated in the range 0.03 to 0.19 mg/m 3 for 480-L samples [1,5]. The substance used to generate test atmospheres at 25 °C and 760 mm Hg in dry air was a 0.075% solution of Demeton (21% Demeton O, 74.5% Demeton S) in toluene [1,5]. The atmosphere was generated by the aspirator method. Collection efficiencies and recovery were 1.00 for the isomers in the range 5 to 270 mg per sample. Sample filters extracted in toluene immediately and stored one week at ambient conditions gave recoveries of 100%. Overall precision for sampling plus measurement, SˆrT, was 0.08. No significant bias was found for either substance. No breakthrough was observed after 12 hours of sampling at 1 L/min in atmospheres containing 0.14 mg/m Demeton O and 0.17 mg/m 3 Demeton S at 80% RH.

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94

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