Page:NIOSH Manual of Analytical Methods - 7900.pdf/2

ARSENIC and compounds, as As: METHOD 7900, Issue 2, dated 15 August 1994 - Page 2 of 3 REAGENTS:  Nitric acid, conc. Hydrochloric acid, conc. Sulfuric acid, conc. Perchloric acid, conc.* Calibration stock solution, 1000 mg/mL.* Commercially available or dissolve 1.320 g primary standard As 2O3 in 25 mL 20% (w/v) KOH. Neutralize with 20% (v/v) HNO 3 to a phenolphthalein endpoint. Add 10 mL conc. HNO3 and dilute to 1 L with distilled or deionized water. Ashing acid, 3 volumes HNO 3, 1 volume H2SO4, and 1 volume HClO 4. Hydrogen. <li>Argon.</li> <li>Distilled or deionized water.</li> <li>Sodium borohydride, pellets.</li> <li>Air, compressed.</li> </ol>


 * See SPECIAL PRECAUTIONS.

EQUIPMENT: <li>Sampler: cellulose ester filter, 0.8-μm pore size, 37-mm diameter; in cassette filter holder.</li> <li>Personal sampling pump, 1 to 3 L/min, with flexible connecting tubing.</li> <li>Atomic absorption spectrophotometer with appropriate hydrogen burner head or quartz tube furnace, and arsenic hollow cathode lamp or EDL and arsine generation system.</li> <li>Regulators, two-stage, for air, hydrogen and argon.</li> <li>Beakers, Phillips, 125-mL, or Griffin, 50-mL, with watchglass covers.* <li>Volumetric flasks, 25- and 100-mL.*</li> <li>Pipets, volumetric, as needed.*</li> <li>Hotplate, surface temperature 140 °C.</li> </ol>


 * Clean all glassware with conc. nitric acid before use and rinse thoroughly with distilled or deionized water.

Arsenic is a recognized carcinogen. Handle appropriately [2]. Perform all perchloric acid digestions in a perchloric acid 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 3 L/min for a total sample size of 30 to 1000 L. Do not exceed ca. 2 mg total dust loading on the filter.</li> </ol>

SAMPLE PREPARATION: <li>Open the cassette filter holders and transfer the samples and blanks to clean beakers. NOTE: Analyze the backup pad separately if qualitative indication of As 2O3 vapor is desired. Use Method 7901 if quantitative collection of As 2O3 vapor is desired.</li> <li>Add 5 mL ashing acid and cover with a watchglass.</li> <li>Heat on hotplate (140 °C) until the solution is colorless.</li> <li>Add 1 mL conc. HNO 3 and/or 70% HClO 4 drop by drop as needed to complete the ashing.</li> <li>Remove the watchglass.</li> <li>Heat on 140 °C hotplate until dense SO 3 fumes appear.</li> <li>Allow the mixture to cool.</li> <li>Transfer the solution quantitatively to a 25-mL volumetric flask.</li> <li>Dilute to volume with distilled or deionized water.</li> </ol>

CALIBRATION AND QUALITY CONTROL: <li>Prepare working standards. Add known amounts, covering the range 0.2 to 8 μg As/100 mL (0.05 to 2 μg As per sample), of 1000 μg/mL As calibration stock solution to 100-mL volumetric flasks containing 4 mL conc. H 2SO4 and dilute to volume with distilled or deionized water.</li> </ol> NIOSH Manual of Analytical Methods (NMAM), Fourth Edition 8/15/94