TUNGSTEN (soluble and insoluble): METHOD 7074, Issue 2, dated 15 August 1994 - Page 2 of 3 REAGENTS: 1. 2. 3. 4. 5. 6. 7.
8.
EQUIPMENT:
Nitric acid, conc.* Hydrofluoric acid, conc.* Hydrochloric acid, conc.* Hydrochloric acid, 1% (v/v). Add 26.5 mL conc. HCl to 500 mL water; dilute to 1 L. Sodium hydroxide, 0.5 M. Dissolve 20 g NaOH in 500 mL water; dilute to 1 L. Sodium sulfate, 20% (w/v). Dissolve 20 g Na 2SO 4 in 80 mL water; dilute to 100 mL. Calibration stock solution, 10 mg W/mL. Commercially available or dissolve 1.5985 g Na 2WO 4 (dried at 125 °C) in water; add 10 mL 0.5 M NaOH and dilute to 100 mL. Water, distilled, deionized.
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 4 L/min, with flexible connecting tubing. 3. Atomic absorption spectrophotometer with a nitrous oxide-acetylene burner head. 4. Tungsten hollow cathode lamp. 5. Two-stage regulators for N 2O and acetylene. 6. Beakers, PTFE, 100-mL (with covers).* 7. Volumetric flasks, 10-, 25- and 100-mL.* 8. Assorted volumetric pipets, as needed, with pipet bulb.* 9. Hotplate for use at 150 °C. 10. Steam bath or 100 °C hotplate. 11. Filtering apparatus (funnel, clamp, frit, holder) with 47-mm, 0.45-µm pore size cellulose ester membrane filter and collection vessel.
Clean all labware with conc. nitric acid and rinse thoroughly with distilled water before use.
SPECIAL PRECAUTIONS: Wear protective equipment (gloves, labcoats, and safety glasses) when working with HF. Do not use HF with glass labware. 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 4 L/min for a total sample size of 200 to 1000 L. Do not exceed 2 mg total dust loading on the filter.
SAMPLE PREPARATION: 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14.
Open the cassette and transfer the filter to the filtering apparatus on top of a 47-mm filter. Add 3 mL deionized water to the sample filter, allow it to stand 3 min, apply vacuum to transfer the extract to the holding vessel, and repeat with an additional 3 mL water. Transfer the extracts to a 10-mL volumetric flask, add 1.0 mL 20% Na 2SO 4, dilute to volume, and analyze for soluble tungsten (steps 17 through 19). Digest the filters and residue in a covered PTFE beaker with 5.0 mL conc. HNO 3 and 5.0 mL conc. HF at 150 °C. Remove the beaker cover and reduce the volume to 2 mL (150 °C). Take to dryness at 100 °C. Remove from heat, cool, add 10 mL 1% HCl, and agitate manually for 5 min. Filter through an additional 47-mm filter (the filtrate may be analyzed for cobalt). Digest the filter and residue in a PTFE beaker with 5.0 mL conc. HNO 3 and 5.0 mL conc. HF at 150 °C. Remove the beaker cover and reduce the volume to 1 mL (150 °C). If filter residue (dark, charred material) is visible, add additional HNO 3 and HF (2 mL each). Take to near-dryness at 100 °C. Dissolve residue in beaker with 2.5 mL 0.5 M NaOH and 2.5 mL 20% Na 2SO 4 at 100 °C (15 min). Transfer to a 25-mL volumetric flask and dilute to volume.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94
