Page:NIOSH Manual of Analytical Methods - 2517.pdf/3

PENTACHLOROETHANE: METHOD 2517, Issue 2, dated 15 August 1994 - Page 3 of 4

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CALIBRATION AND QUALITY CONTROL:  

9. Calibrate daily with at least six working standards over the range 0.004 to 40 µg pentachloroethane per sample (0.002 to 20 µg/mL).
   1. Add known amounts of calibration stock solution, or serial dilutions thereof, to hexane in 10-mL volumetric flasks and dilute to the mark.
      NOTE: The working standards are stable indefinitely at room temperature if kept in airtight containers.
   2. Analyze together with samples and blanks (steps 12 and 13).
   3. Prepare calibration graph (peak area or height vs. µg pentachloroethane).
10. Determine desorption efficiency (DE) at least once for each lot of Porapak R used for sampling in the calibration range (step 9). Prepare three tubes at each of five levels plus three media blanks.
    1. Remove and discard back sorbent section of a media blank sampler.
    2. Inject a known amount (1 to 20 µL) of calibration stock solution, or serial dilutions thereof, directly onto front sorbent section with a microliter syringe.
    3. Cap the tube. Allow to stand overnight.
    4. Desorb (steps 6 through 8) and analyze together with working standards (steps 12 and 13).
    5. Prepare a graph of DE vs. µg pentachloroethane recovered.
11. Analyze three quality control blind spikes and three analyst spikes to ensure that the calibration graph and DE graph are in control.

MEASUREMENT:  

12. Set gas chromatograph according to manufacturer's recommendations and to conditions given on page 2517-1. Inject sample aliquot manually using solvent flush technique or with autosampler. t_r = 3.5 min at these conditions.
    NOTE: If peak area is above the linear range of the working standards, dilute with hexane, reanalyze, and apply the appropriate dilution factor in calculations.
13. Measure peak area or height.

CALCULATIONS:  

14. Determine the mass, µg (corrected for DE) of pentachloroethane 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.
15. Calculate concentration, C, of pentachloroethane in the air volume sampled, $V$ (L):

    $C={\frac {W_{f}+W_{b}-B_{f}-B_{b}}{C}}$, mg/m³

EVALUATION OF METHOD:  

P&CAM 335 was issued on August 29, 1980, and validated over the range 0.014 to 5.4 mg/m³ with samples from dynamically generated test atmospheres [1]. A gas chromatograph with gas sampling loop was used to monitor pentachloroethane concentration of the atmospheres. To study sample stability, four sets of six 3-L samples of 0.014 mg/m 3 pentachloroethane at 80% relative humidity were obtained. The samples were stored at room temperature for the first 7 days, and at 0 °C for the remainder of the period. These sets were analyzed at day 1, 7, 14, and 28. The mean recoveries were, respectively, 104, 105, 101.4, and 97.0%. The respective relative standard deviations were 7.4, 6.2, 9.0, and 16.7%. The breakthrough volume for the 70-mg bed of Porapak R was 14 L, when an atmosphere at 40 °C containing 126 mg/m³ pentachloroethane and >80% relative humidity was sampled at 0.2 L/min.

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