Page:NIOSH Manual of Analytical Methods - 7900.pdf/3

 ARSENIC and compounds, as As: METHOD 7900, Issue 2, dated 15 August 1994 - Page 3 of 3 13. 14. 15. 16. 17.

Analyze working standards together with the blanks and samples (steps 18 through 25). Prepare calibration graph (absorbance vs. solution concentration, µg/mL). Analyze a standard for every 10 samples. Check analytical recoveries with at least one spiked media blank per 10 samples. Use method of standard additions occasionally to check for interferences.

ANALYTICAL PROCEDURE: 18. 19. 20. 21. 22. 23. 24. 25.

Set spectrophotometer according to manufacturer's recommendations and to conditions on page 7900-1. Set up arsine generator per manufacturer's instructions. Pipet 5 mL aliquot of the 25-mL sample into the arsine generation flask. Add 25 mL distilled or deionized water, 3 mL conc. HCl, and mix well. Connect the flask to the generation system. Introduce a single sodium borohydride pellet or sodium borohydride solution to the sample solution. Allow the gases to flush into the flame of the atomic absorption instrument. Record the absorbance readings. NOTE: If the absorbance values of the samples are above the linear range of the standards, dilute the solutions, or use a smaller aliquot, reanalyze, and use the appropriate dilution factor in calculations.

CALCULATIONS: 26. 27.

Using the measured absorbances, calculate the corresponding solution concentrations (µg/mL) of As in the sample, C s, and average media blank, C b, from the calibration graph. Using the solution volumes (mL) of the sample, V s, and media blanks, V b, calculate the concentration, C (mg/m 3), of As in the air volume sampled, V (L):

EVALUATION OF METHOD: This method was evaluated in July, 1976, over the range 0.02 to 3 mg per sample by laboratory testing with spiked filters. Precision and accuracy data are given on page 7900-1 [1].

REFERENCES: [1] [2]

NIOSH Manual of Analytical Methods, 2nd. ed., V. 1, P&CAM 139, U.S. Department of Health, Education, and Welfare, Publ. (NIOSH) 77-157-A (1977). Criteria for a Recommended Standard...Occupational Exposure to Inorganic Arsenic, U.S. Department of Health, Education, and Welfare, Publ. (NIOSH) 75-149 (1975).

METHOD WRITTEN BY: Mark Millson, NIOSH/DPSE.

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