National Institute for Occupational Safety and Health

“ Steps 4 through 9 of Method 7300 or other quantitative ashing techniques may be necessary for some samples, especially if several metals are to be determined on a single filter. Open the cassette filter holders and transfer the samples and blanks to clean beakers. Add 3 mL aqua regia, cover with a watchglass, let stand at room temperature 30 min. Start reagent blanks at this point. Heat on hotplate (140 C) until most of the acid has evaporated (ca. 0.5 mL remains) . Repeat 2 more times using 3 mL conc. HNO3 each time. Leave about 1 mL solution after thelast digestion. Cool each beaker. ”

“ Add known amounts, covering the expected range of samples (0 to 60 μg Co per sample) , of calibration stock solution to 10-mL volumetric flasks and dilute to volume with 5% HNO3. Analyze the working standards together with the blanks and samples (steps 17 and 18) . NIOSH Manual of Analytical Methods (NMAM) , Fourth Edition Cobalt and compounds, as Co: Method 7027, Issue 2, dated 15 August 1994 - Page 3 of 3 13. 14. 15. 16.
Prepare a calibration graph of absorbance vs. solution concentration (μg/mL) . Aspirate a standard for every 10 samples to check instrument drift. ”

“ Method 7027, Issue 2, dated 15 August 1994 - Page 2 of 3 REAGENTS:
EQUIPMENT:
1. Nitric acid (HNO3, conc. 2. Hydrochloric acid (HCl) , conc. 3. Aqua regia: mix 3 volumes conc. HCl with 1 volume conc. HNO3. 4. Nitric acid, 5% (w/v) . ”