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ARSENIC and compounds, as As: METHOD 7900, Issue 2, dated 15 August 1994 - Page 3 of 3

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


ANALYTICAL PROCEDURE:  

  1. Set spectrophotometer according to manufacturer's recommendations and to conditions on page 7900-1.
  2. Set up arsine generator per manufacturer's instructions.
  3. Pipet 5 mL aliquot of the 25-mL sample into the arsine generation flask.
  4. Add 25 mL distilled or deionized water, 3 mL conc. HCl, and mix well.
  5. Connect the flask to the generation system.
  6. Introduce a single sodium borohydride pellet or sodium borohydride solution to the sample solution.
  7. Allow the gases to flush into the flame of the atomic absorption instrument.
  8. 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:  

  • Using the measured absorbances, calculate the corresponding solution concentrations (μg/mL) of As in the sample, C s, and average media blank, Cb, from the calibration graph.
  • Using the solution volumes (mL) of the sample, V s, and media blanks, V b, calculate the concentration, C (mg/m³), of As in the air volume sampled, V (L):

    , mg/m³

    • 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] 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).

    [2] 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

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