National Institute for Occupational Safety and Health

“ Analyze the working standards together with the blanks and samples (steps 15 and 16) . Prepare a calibration graph of absorbance vs. solution concentration (μg/mL) . Aspirate a standard for every 10 samples to check instrument drift. Check analytical recoveries with at least one spiked media blank per 10 samples. Use method of standard additions occasionally to check for interferences.
MEASUREMENT: 15.
16.
Set spectrophotometer as recommended by the manufacturer and to conditions on page 7024-1. NOTE: Air-acetylene flame may also be used. ”

“ A reducing air-C2H2 flame provides the best sensitivity, but the greatest susceptibility to interference [5] . Aspirate standards and samples. Record absorbance readings NOTE: If the absorbance values for the samples are above the linear range of the standards, dilute the solutions with 5% HNO3, reanalyze, and apply the appropriate dilution factor in the calculations.
CALCULATIONS: 17. 18.
Using the measured absorbances, calculate the corresponding solution concentrations (μg/mL) of chromium in the sample, Cs, and average media blank, Cb, from the calibration graph. ”

“ The working range is 0.05 to 2.5 mg/m3 for a 100-L air sample. This is an elemental analysis for total Cr, not compound specific. Some compounds of Cr may not be dissolved by this method. Aliquots can be analyzed separately for approximately four additional metals. ”