Page:NIOSH Manual of Analytical Methods - 6001.pdf/3

 ARSINE: METHOD 6001, Issue 2, dated 15 August 1994 - Page 3 of 4 7. 8.

Agitate for 30 min in an ultrasonic bath. Centrifuge each tube.

CALIBRATION AND QUALITY CONTROL: 9.

10.

11.

Calibrate daily with at least six working standards over the range 0.004 to 0.3 µg arsenic per sample. a. Add known amounts of calibration stock solution and 0.01 M HNO 3 for a 1.0-mL final solution volume to centrifuge tubes containing 100 mg activated charcoal from a media blank sampler. b. Analyze standards together with samples and blanks (steps 12 and 13). Analyze a working standard for every five samples to check for instrument drift. c. Prepare a calibration graph (absorbance vs. µg arsenic). Determine desorption efficiency (DE) at least once for each batch of charcoal used for sampling in the range 0.004 to 2 µg arsenic per sample. Prepare three tubes at each of five levels plus three media blanks. a. Remove and discard back sorbent section of a media blank sampler. b. Inject a known amount of pure arsine gas (or a certified gas mixture containing arsine) directly onto front sorbent section with a microliter syringe. c. Cap the tube. Allow to stand overnight. d. Desorb (steps 5 through 8) and analyze together with working standards (steps 12 and 13). e. Prepare a graph of DE vs. µg arsenic recovered. Analyze three quality control spikes to ensure that the calibration graph is in control.

MEASUREMENT: 12. 13.

Set the spectrophotometer and furnace to manufacturer's recommendations and to conditions given on page 6001-1. Inject a 50-µL aliquot of sample or standard followed by a 50-µL aliquot of nickel nitrate solution prior to initiating the analysis program. Measure peak area. NOTE 1: If sample absorbance is above the linear range of the standards, dilute with 0.01 M HNO 3, reanalyze and apply the appropriate dilution factor in calculations. NOTE 2: Monitor the reproducibility of peak area for a working standard throughout the measurements. If erratic results occur, reoptimize instrumental parameters and replace the graphite tube.

CALCULATIONS: 14.

15.

Determine the mass, µg, of arsine 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 by multiplying the mass of arsenic found for each of these sections by 1.040 (M.W. of arsine/M.W. of arsenic). NOTE: If W b > W f/10, report breakthrough and possible sample loss. Calculate concentration, C, of arsine in the air volume sampled, V (L):

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