Page:NIOSH Manual of Analytical Methods - 3704.pdf/3

 PERCHLOROETHYLENE (portable GC) in exhaled breath and air: METHOD 3704, Issue 1, dated 15 January 1998 - Page 3 of 5

concentration in those subsequent samples. Pump air sample into bag at a rate calculated to fill 80% of the bag capacity over the sampling period. NOTE: The flow rate must be constant throughout the sampling period. d. As soon as practical, but within 8 h after completion of sampling, introduce an aliquot of the sample into the GC (step 2). 4. Exhaled Breath Sample (adapted from Toutonghi [4]) a. Move subject to an area where ambient analyte concentrations are insignificant. b. Instruct subject to take 4 normal breaths followed by 1 deep inhalation. c. Hold the deep breath for 10 seconds. d. After 10 seconds, exhale the first half of the breath into the room and the last half through a tube filled with Dry-Rite into a sampling bag. f. Close the bag valve and queue the sample for analysis. 5. Obtain the perchloroethylene peak height or area of the injected sample (see Figure 1). c.

CALIBRATION AND QUALITY CONTROL: 6. Perform the following in the laboratorybefore field work begins: a. Establish a laboratory calibration graph with at least three replicate determinations of six or more working standards. Plot peak height or area vs. mass or concentration of perchloroethylene. b. Determine detector drift, averaged over the time period(s) expected to be used in the field. c. Determine the ability of the GC column to separate the perchloroethylene peak from other substances known or predicted to be present in the field samples. 7. Establish a daily field calibration graph (peak height vs. mass or concentration of perchloroethylene). a. Fill Tedlar bags with standards, preferably commercially prepared and certified, or inject known amounts of pure perchloroethylene into Tedlar bags containing a metered volume of pure air or nitrogen. (See APPENDIX) b. Analyze working standards in triplicate under the same conditions as samples. c. Alternate analyses of samples and working standards, if possible. CALCULATIONS: 8. Determine mass, W (ppm), of perchloroethylene by comparison of sample peak height with daily calibration graph (step 7). Calculate concentration, C, of perchloroethylene in the sample volume 3 injected, V (mL), applying the factor 6.8 to convert ppm to mg/m at NTP.

C

6.8 W, mg/m 3 V

NOTE 1: µg/mL mg/m3 NOTE 2: Some GCs will perform this calculation electronically if programmed appropriately during the calibration phase.

EVALUATION OF METHOD: This method was evaluatedover the range 0.1 to 100 ppm perchloroethylene in air using a Photovac 10S portable gas chromatograph(Photovac International, Deer Park, NY). Certified standard gas mixtures of 1.0 ppm perchloroethylene in air were obtained from Scott Specialty Gases, Inc., (Troy, MI) These were verified by comparison with standards prepared from liquid and were then used to establish the calibration graphs. Analytical precision was determined by calculating the variation of replicate analyses of calibration standards and samples. Oncecalibration graphs were established, bias was assessed by analyzing a bag sample containing an unknown concentration and comparing the concentration obtained with that obtained from analysis of replicate charcoal tubes samples taken from the same bag. Additionally, a field evaluation was subsequently conducted in which results obtained using this method averaged 6% higher than results NIOSH Manual of Analytical Methods (NMAM), Fourth Edition