Page:NIOSH Manual of Analytical Methods - 7027.pdf/2

 Cobalt and compounds, as Co: 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). Add 50 mL conc. HNO3 to water; dilute to 1 L. 5. Calibration stock solution, 1000 µg/mL Co. Commercially available or dissolve 1.000 g Co metal in minimum volume of aqua regia. Dilute to 1 L with 5% HNO3. 6. Distilled or deionized water. 7. Air, filtered. 8. Acetylene.

1. Sampler: cellulose ester membrane filter, 0.8-µm pore size, 37-mm diameter; in cassette filter holder. 2. Personal sampling pump, 1 to 3 L/min, with flexible connecting tubing. 3. Atomic absorption spectrophotometer with an air-acetylene burner head and cobalt hollow cathode lamp. 4. Regulators, two-stage, for air and acetylene. 5. Beakers, Phillips, 125-mL, or Griffin, 50-mL, with watchglass covers.* 6. Volumetric flasks, 10- and 100-mL.* 7. Micropipets, 5- to 60-µL.* 8. Hotplate, surface temperature 140 C.

Clean with conc. HNO3 and rinse thoroughly with distilled or deionized water before use.

SPECIAL PRECAUTIONS: Perform all acid digestions in a fume hood.

SAMPLING: 1. 2.

Calibrate each personal sampling pump with a representative filter in line. Sample at an accurately known flow rate between 1 and 3 L/min for a sample size of 30 to 1500 L. Do not exceed a filter loading of approximately 2 mg total dust.

SAMPLE PREPARATION: NOTE:

3. 4. 5. 6. 7. 8. 9. 10.

The following sample preparation gave quantitative recovery (see EVALUATION OF METHOD). 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. Remove watchglass and rinse into the beaker with 5% HNO 3. Dissolve the residues in 2 to 3 mL 5% HNO . 3 Transfer the solution quantitatively to a 10-mL volumetric flask. Dilute to volume with 5% HNO3.

CALIBRATION AND QUALITY CONTROL: 11.

12.

Calibrate daily with at least six working standards. 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