Page:NIOSH Manual of Analytical Methods - 2530.pdf/3

 DIPHENYL: METHOD 2530, Issue 2, dated 15 August 1994 - Page 3 of 4 CALIBRATION AND QUALITY CONTROL: 8.

9.

10.

Calibrate daily with at least six working standards over the range 0.1 to 120 µg diphenyl per sample. Use serial dilutions for the smallest concentrations. a. Add known amount of calibration stock solution to CCl 4 in 10-mL volumetric flask and dilute to the mark. b. Analyze with samples and blanks (steps 11 and 12). c. Prepare calibration graph (peak height or area vs. µg diphenyl per sample). 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 levels plus three media blanks. a. Remove and discard back sorbent section of a media blank sampler. b. Inject 2 to 10 µL of DE stock solution (or of a serially diluted solution in hexane) 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. µg diphenyl 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 2530-1. Inject sample aliquot manually using solvent flush technique or with autosampler. NOTE 1: If peak area is above the linear range of the working standards, dilute an aliquot of the desorbed liquid with CCl 4, reanalyze and apply the appropriate dilution factor in calculations. NOTE 2: Under these conditions, t r for diphenyl is approximately 6 min. Measure peak height or area.

CALCULATIONS: 13.

14.

Determine the mass, µg (corrected for DE) of diphenyl 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 diphenyl in the air volume sampled, V (L):

EVALUATION OF METHOD: Method S24 was issued on November 25, 1977 [2], and validated over the range 0.64 to 2.4 mg/m 3 using 32-L samples collected on Tenax GC, Lot 04901 (Applied Science Laboratories) [1]. The diphenyl concentration was independently determined by UV analysis of samples collected in methanol. Overall precision, SˆrT, was 0.068 with an average recovery of 92.7%. Desorption efficiency averaged 0.987 in the range 19 to 76 µg per sample. For samples collected at 2.5 mg/m 3, 25 °C, and >85% RH, breakthrough to the backup section averaged 3.9% between 31.5 and 48.6 L, and 9.4% between 48.6 and 64.2 L. Recovery from a set of samples stored one week under ambient conditions was 95.0% relative to a set analyzed immediately. Previous work showed desorption efficiency to be poor (<0.7) for diphenyl on SKC Lots 104 and 105 charcoals [1,3]. NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94