HYDROGEN SULFIDE: METHOD 6013, Issue 1, dated 15 August 1994 - Page 3 of 4 8. 9.
Dilute to 10 mL with 3 mL of deionized water. Cap and shake vigorously. Transfer sample to 10-mL plastic syringe fitted with in-line filter.
CALIBRATION AND QUALITY CONTROL: 10. Calibrate daily with at least six working standards over the range 0.1 to 20 µg sulfate ion per mL of sample (1 to 200 µg per 10 mL). a. Add known amounts of calibration stock solution to deionized water in 10- or 25-mL volumetric flasks and dilute to the mark. Prepare fresh working standards biweekly. b. Analyze together with samples and blanks (steps 14 and 15). c. Prepare calibration graph (peak height vs. µg SO 24- per sample). 11. Determine desorption efficiency (DE) at least once for each lot of charcoal used for sampling in the calibration range (step 10). Prepare four tubes at each of three levels plus three media blanks. a. Generate concentrations of H 2S from a calibration gas mixture or a permeation device. Mix with dilution air as necessary. b. Collect samples at a flow rate of 1 L/min for 30 min. c. Cap the tubes and allow to stand overnight. d. Desorb (steps 5 through 9) and analyze together with working standards (steps 14 and 15). e. Prepare a graph of DE vs. µg sulfate recovered. 12. Analyze three quality control blind spikes and three analyst spikes to insure that the calibration graph is in control.
MEASUREMENT: 13. Set ion chromatograph according to manufacturer's recommendations and to conditions given on page 6013-1. 14. Inject a 50-µL sample aliquot manually or with autosampler. 15. Measure peak height. NOTE: If peak height is above the linear range of the working standards, dilute with deionized water, reanalyze, and apply the appropriate dilution factor in calculations.
CALCULATIONS: 16. Determine the mass, µg (corrected for DE) of sulfate ion 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. 17. Calculate concentration, C, of hydrogen sulfide in the air volume sampled, V (L), applying the factor 0.3548 (MW H 2S/MW SO 24-) for the conversion of SO 24- to H 2S:
EVALUATION OF METHOD: The method was evaluated by sampling generated test atmospheres of H 2S in air [1]. Time-weighted average samples were taken at four concentration levels over a range of 1.4 to 22 mg/m 3 (1 to 16 ppm). For ceiling concentrations or short-term exposure limits, 15-L samples were collected at 1 L/min. Breakthrough was determined for coconut charcoal from a generated atmosphere at a concentration of 20 ppm (2 x PEL) and at both low (~20%) and high (~80%) relative humidity (RH). Breakthrough volumes for low and high RH were 21 L and 84 L, respectively, corresponding to capacities of 588 µg of H 2S (low RH) and 2352 µg of H 2S (high RH). At 1 x PEL, the equivalent breakthrough volume is 42 L (low RH) and 164 L (high RH). Large coconut charcoal tubes have sufficient capacity to collect a 4-h sample at the PEL of 10 ppm, as well as STEL samples (15 ppm for 15 min). H 2S samples are stable for at least NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94
