Page:NIOSH Manual of Analytical Methods - 1024.pdf/4

1,3-BUTADIENE: METHOD 1024, Issue 2, dated 15 August 1994 - Page 4 of 8

e. Store at temperature below –4 °C overnight, then desorb (steps 5 through 8). f. Analyze media standards and blanks together with samples (steps 13 and 14). g. Convert gas volumes to masses, correcting for compressibility and water vapor (see APPENDIX B), and prepare a calibration graph (peak areas or heights vs. concentration of 1,3-butadiene taken in µg/mL). 11. Determine desorption efficiency (DE) at least once for each lot of charcoal used for sampling in calibration range (step 10). a. Dilute the stock solutions (step 9) with methylene chloride to extend the range of standards down to 0.1 µg/mL. Avoid including water in the portions diluted. b. Transfer solutions as in step 8 if using an autosampler, and analyze together with media standards (steps 13 and 14). c. Convert gas volumes to masses, correcting for compressibility and water vapor (see APPENDIX B), and prepare DE calibration graph of peak area or height vs. µg/mL 1,3-butadiene. d. Read the concentrations, µg/mL, in media standards and blanks from DE calibration graph and multiply by the desorption volume to calculate the masses recovered. e. Prepare a graph of DE vs. µg taken. DE = (mass found – blank mass)/(mass taken). 12. Analyze three quality control blind spikes to insure that calibration graph (step 10) is in control. MEASUREMENT: 13. Set gas chromatograph according to manufacturer’s recommendations and to conditions given on page 1024-1. Inject sample aliquot manually using solvent flush technique or with autosampler. NOTE: If detector response is above range of working standards, dilute with methylene chloride, reanalyze, and apply appropriate dilution factor in calculations. 14. Measure peak area or height. NOTE: Vinylidene chloride, an impurity in methylene chloride, elutes just after 1,3-butadiene and may be used as an internal standard. CALCULATIONS: 15. Determine the concentration, µg/mL, of 1,3-butadiene found in each sample front ( ) and back ( ) sorbent section from calibration graph (step 10), and multiply by desorption volume, , mL, and dilution factor, if any, to calculate the mass, µg, found. NOTE 1: This calibration method corrects for media blank and DE. Do not duplicate corrections. NOTE 2: For any sampler with >  /10, report breakthrough and possible sample loss. , mg/m³. EVALUATION OF METHOD: The detector responses determined for triplicate standard solutions at each of five levels were linear over the range 0.3 to 440 µg per sample. The pooled was 0.038. The estimated LOD was 0.02 µg/mL. The capacity of a 400-mg charcoal sorbent section was 31 L for a sample at 80% RH and approximately 56 ppm 1,3-butadiene. When exposed to 0.7 and 2.5 mL of pure 1,3-butadiene gas followed by 80% RH air, breakthrough occurred after 35 L and 28.5 L, respectively. The corresponding respective timeweighted average concentrations were 20 and 88 ppm. For the analysis of media standards at levels of 1.1, 4.4, 18, 125, and 480 µg per sample, the pooled was 0.025, and the desorption efficiencies were 67%, 68%, 75%, 102%, and 97%, respectively. Adding water to media standards just after spiking or during desorption had no significant effect on desorption efficiencies. NIOSH Manual of Analytical Methods (NMAM), Fourth Edition