Page:NIOSH Manual of Analytical Methods - 7074.pdf/2

TUNGSTEN (soluble and insoluble): METHOD 7074, Issue 2, dated 15 August 1994 - Page 2 of 3 REAGENTS

 Nitric acid, conc.* Hydrofluoric acid, conc.* ydrochloric acid, conc.* Hydrochloric acid, 1% (v/v). Add 26.5 mLconc. 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 Na₂SO₄ in 80 mL water; dilute to 100 mL. Calibration stock solution, 10 mg W/mL. Commercially available or dissolve 1.5985 g Na₂WO₄(dried at 125 °C) in water; add 10 mL 0.5 M NaOH and dilute to 100 mL. <li>Water, distilled, deionized.</li> </ol>


 * See SPECIAL PRECAUTIONS.

EQUIPMENT:

<ol> <li>Sampler: cellulose ester membrane filter, 0.8-μm pore size, 37-mm diameter; in cassette filter holder.</li> <li>Personal sampling pump, 1 to 4 L/min, with flexible connecting tubing.</li> <li>Atomic absorption spectrophotometer with a nitrous oxide-acetylene burner head.</li> <li>Tungsten hollow cathode lamp.</li> <li>Two-stage regulators for N ₂ O and acetylene.</li> <li>Beakers, PTFE, 100-mL (with covers).*</li> <li>Volumetric flasks, 10-, 25- and 100-mL.*</li> <li>Assorted volumetric pipets, as needed, with pipet bulb.*</li> <li>Hotplate for use at 150 °C.</li> <li>Steam bath or 100 °C hotplate.</li> <li>Filtering apparatus (funnel, clamp, frit, holder) with 47-mm, 0.45-μm pore size cellulose ester membrane filter and collection vessel.</li> </ol>


 * 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 <ol> <li>Calibrate each personal sampling pump with a representative sampler in line.</li> <li>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.</li> </ol>

SAMPLE PREPARATION: <li>Open the cassette and transfer the filter to the filtering apparatus on top of a 47-mm filter.<li> <li>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.</li> <li>Transfer the extracts to a 10-mL volumetric flask, add 1.0 mL 20% Na ₂SO₄, dilute to volume, and analyze for soluble tungsten (steps 17 through 19). <li>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.</li> <li>Remove the beaker cover and reduce the volume to 2 mL (150 °C). Take to dryness at 100 °C.</li> <li>Remove from heat, cool, add 10 mL 1% HCl, and agitate manually for 5 min.</li> <li>Filter through an additional 47-mm filter (the filtrate may be analyzed for cobalt).</li> <li>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.</li> <li>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).</li> <li>Take to near-dryness at 100 °C.</li> <li>Dissolve residue in beaker with 2.5 mL 0.5 M NaOH and 2.5 mL 20% Na₂SO₄ at 100 °C (15 min).</li> <li>Transfer to a 25-mL volumetric flask and dilute to volume</li> </ol> NIOSH Manual of Analytical Methods (NMAM), Fourth Edition