Page:NIOSH Manual of Analytical Methods - 7024.pdf/2

 CHROMIUM and compounds, as Cr: METHOD 7024, Issue 2, dated 15 August 1994 - Page 2 of 4 REAGENTS:

EQUIPMENT:

1. Nitric acid, conc. 2. Hydrochloric acid, conc. 3. Nitric acid, 5%. Add 50 mL conc. HNO3 to water; dilute to 1 L. 4. Calibration stock solution, 1000 µg/mL Cr. Dissolve 3.735 g K2CrO4 or 2.829 g K2Cr2O7 in distilled or deionized water to make 1 L solution. 5. Distilled or deionized water. 6. Nitrous oxide. 7. Acetylene.


 * See SPECIAL PRECAUTIONS.

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 a nitrous oxide-acetylene burner head and chromium hollow cathode lamp. 4. Regulators, two-stage, for nitrous oxide and acetylene. 5. Beakers, Phillips, 125-mL, or Griffin, 50-mL, with watchglass covers.* 6. Volumetric flasks, 100-mL.* 7. Graduated centrifuge tubes, 15-mL.* 8. Assorted volumetric pipets, as needed.* 9. Hotplate, surface temperature to 140 °C.

Clean all glassware with nitric acid 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 sampler in line. Sample at an accurately known flow rate between 1 and 3 L/min for a sample size of 10 to 1000 L. Do not exceed a filter loading of ca. 2 mg total dust.

SAMPLE PREPARATION:

3. 4.

5. 6. 7. 8.

NOTE: The following sample preparation gave quantitative recovery (see EVALUATION OF METHOD) [2,3]. 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 cassettes and filter holders and transfer the samples and blanks to clean beakers. Add 3 mL conc. HCl, cover with a watchglass, heat on hotplate (140 °C) until the volume is reduced to ca. 0.5 mL. Repeat two more times using 3 mL conc. HCl. NOTE: Start reagent blanks at this step. Add 3 mL conc. HNO3, cover with a watchglass, heat on hotplate (140 °C) until the volume is reduced to ca. 0.5 mL. Repeat two more times using 3 mL conc. HNO3. Cool solution and dissolve the residues in 1 mL conc. HNO3. Transfer the solution quantitatively to a 15-mL graduated centrifuge tube. Dilute to volume with distilled water.

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