Page:NIOSH Manual of Analytical Methods - 1002.pdf/3

 β-CHLOROPRENE: METHOD 1002, 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 0.03 to 0.5 mg chloroprene per sample. a. Add known amounts of calibration stock solution below the surface of CS 2 in 10-mL volumetric flasks and dilute to the mark. b. Analyze together with samples and blanks (steps 11 and 12). c. Prepare calibration graph (peak area vs. mg chloroprene). Determine desorption efficiency (DE) at least once for each batch of charcoal used for sampling in the calibration range (step 8). 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 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. mg chloroprene 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 1002-1. Inject sample aliquot either with autosampler or manually using solvent flush technique. NOTE: If peak area is above the linear range of the working standards, dilute 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 chloroprene 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 chloroprene in the air volume sampled, V (L):

EVALUATION OF METHOD: Method S112 was issued on October 29, 1976, and validated over the range 44 to 175 mg/m 3 with eighteen 3-L samples from dynamically-generated test atmospheres, as well as a set of six samples at one times the OSHA standard concentration stored at room temperature for eight days to establish stability [2,5]. Eighteen more samples were spiked (six each at one-half, one and two times the OSHA standard, 0.14 to 0.54 mg) directly. The pooled precision ( Sr) for these three sets of analytical samples was 0.021. The average recovery for all three concentrations was 98.8%, representing a non-significant bias. The value for the taken concentration was obtained by monitoring during generation with a gas chromatograph with a 2-mL sampling loop. Bag standards were used to calibrate the gas chromatograph. The stored samples results were within 1% of samples analyzed after one day, indicating adequate storage stability for eight days. Six parallel breakthrough tubes were run at a time. The generated atmosphere was pulled through the charcoal tubes (critical orifices to control flow). NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94