Page:NIOSH Manual of Analytical Methods - 7600.pdf/2

 CHROMIUM, HEXAVALENT: METHOD 7600, Issue 2, dated 15 August 1994 - Page 2 of 4 EQUIPMENT:

REAGENTS: 1. 2.

Sulfuric acid, conc. (98% w/w). Sulfuric acid, 6 N. Add 167 mL conc. H 2SO 4 to water in a 1-L flask; dilute to the mark. 3. Sulfuric acid, 0.5 N. Add 14.0 mL conc. H2SO 4 to water in a 1-L flask; dilute to the mark. 4. Sodium carbonate, anhydrous. 5. Sodium hydroxide. 6. Potassium chromate. 7. Diphenylcarbazide solution. Dissolve 500 mg sym-diphenylcarbazide in 100 mL acetone and 100 mL water. 8. Cr(VI) standard, 1000 µg/mL. Dissolve 3.735 g K 2CrO 4 in deionized water to make 1 L, or use commercially available solution.* 9. Calibration stock solution, 10 µg/mL. Dilute 1000 µg/mL Cr(VI) standard 1:100 with deionized water. 10. Filter extraction solution, 2% NaOH-3% Na 2CO 3. Dissolve 20 g NaOH and 30 g Na 2CO 3 in deionized water to make 1 L of solution. 11. Nitrogen, purified.

1. Sampler: polyvinyl chloride (PVC) filter, 5.0-µm pore size, 37-mm diameter in polystyrene cassette filter holder (FWSB [MSA] or VM-1 [Gelman] or equivalent). NOTE: Some PVC filters promote reduction of Cr(VI). Check each lot of filters for recovery of Cr(VI) standard. 2. Personal sampling pump, 1 to 4 L/min, with flexible connecting tubing. 3. Vials, scintillation, 20-mL glass, PTFE-lined screw cap.** 4. Forceps, plastic. 5. Spectrophotometer, UV-visible (540 nm), with cuvettes, 5-cm path length. 6. Filtration apparatus, vacuum.** 7. Beakers, borosilicate, 50-mL.** 8. Watchglass.** 9. Volumetric flasks, 25-, 100- and 1000-mL.** 10. Hotplate, 120 to 400 °C. 11. Micropipettes, 10-µL to 1-mL. 12. Centrifuge tubes, 40-mL, graduated, with plastic stoppers.** 13. Buchner funnel.** 14. Pipettes, TD 5 mL.**

See SPECIAL PRECAUTIONS.

Clean all glassware with 1:1 HNO thoroughly before use.

3

and rinse

SPECIAL PRECAUTIONS: Insoluble chromates are suspected human carcinogens [4]. All sample preparation should be performed in a hood.

SAMPLING: 1. 2. 3.

Calibrate the sampling pump with a representative sampler in line. Sample at an accurately known flow rate in the range 1 to 4 L/min for a sample size of 8 to 400 L. Do not exceed 1 mg total dust loading on the filter. Remove the filter from the cassette within 1 h of completion of sampling and place it in a vial to be shipped to the laboratory. Handle the filter only with forceps. Discard the backup pad.

SAMPLE PREPARATION:

4.

NOTE: There are two sample preparation techniques outlined below. For soluble chromates or chromic acid, follow step 4; for insoluble chromate or Cr(VI) in the presence of Fe, Fe 2+ or other reducing agents, follow step 5. Sample preparation for soluble chromates and chromic acid. a. Remove the blank and sample filters from the vials, then fold and place them into centrifuge tubes. b. Add 6 to 7 mL 0.5 N H2SO 4 to each tube, cap, and shake to wash all surfaces of the filter. Allow filter to remain in tube 5 to 10 min [6]. c. Remove the filter from the tube with plastic forceps, carefully washing all surfaces with an NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94