Page:NIOSH Manual of Analytical Methods - 7901.pdf/3

 ARSENIC TRIOXIDE, as As: METHOD 7901, Issue 2, dated 15 August 1994 - Page 3 of 4 6. 7. 8.

Carefully rinse the material on the bottom of the watchglass, and the sides of the beaker into the sample solution with distilled water. Add 6 mL 30% H 2O 2. Evaporate just to dryness on the steambath. Cool beakers. Add 10.0 mL 1000 µg/mL Ni 2+ solution, cover, and mix for 30 min in an ultrasonic bath.

CALIBRATION AND QUALITY CONTROL: 9. 10.

11. 12.

Dilute the calibration stock solution 1:100 with 1000 µg/mL Ni ++ solution. This standard is 10.0 µg/mL As. Prepare fresh daily. Prepare six working standards covering the range 0 to 1.25 µg/mL As. a. Add aliquots of the 10.0 µg/mL As solution to 10-mL volumetric flasks and dilute to volume with 1000 µg/mL Ni 2+ solution. b. Analyze the working standards together with the samplers and blanks (steps 13 and 14). c. Prepare calibration graph (absorbance vs. solution concentration, µg/mL). Inject a standard for every other sample to check instrument drift. Check recoveries with at least two spiked media blanks per ten samples. Use method of additions occasionally to check for interferences.

MEASUREMENT: 13. 14.

Set spectrophotometer according to manufacturer's recommendations to conditions on page 7901-1. Inject standards and samples. Record absorbance (peak height) readings. NOTE: If the absorbance values for the samples are above the linear range of the standards, dilute the solutions with 1000 µg/mL Ni 2+ solution, reanalyze, and use the appropriate dilution factor in calculations.

CALCULATIONS: 15. 16. 17.

Record the actual solution volumes to which the sample, V s (mL), and media blanks, V b (mL) were diluted in step 8. Calculate the solution concentration of arsenic in the sample, C s (µg/mL), and average media blank, C b (µg/mL), from the calibration graph. Calculate the concentration of arsenic, C (mg/m 3), in the air volume sampled, V(L):

EVALUATION OF METHOD: Method S309 [4] was issued on September 26, 1975, and validated with aerosols generated from As 2O 3 solutions in dilute NaOH [2]. Method P&CAM 346 was developed in August, 1981, over the range 0.67 to 32.2 µg/m 3 for a 400-L air sample, corresponding to 0.268 to 12.8 µg As per sample [1]. Atmospheres were generated by passing air over heated As 2O 3. Collection efficiencies (CE) for As 2O 3 under these conditions were determined to be 0.42 and 0.67 for untreated 0.8-mm cellulose ester membrane filters, and cellulose backup pads, respectively. Under the same conditions, the Na 2CO 3-treated filter had CE = 0.93 [5]. This method was used in a lead-acid battery manufacturing plant in which vapor was found to be significant [10].

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