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

REAGENTS:

1. Nitric acid, conc.
2. Hydrochloric acid, conc.
3. Sulfuric acid, conc.
4. Perchloric acid, conc.*
5. 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.
6. Ashing acid, 3 volumes HNO 3, 1 volume H2SO4, and 1 volume HClO 4.
7. Hydrogen.
8. Argon.
9. Distilled or deionized water.
10. Sodium borohydride, pellets.
11. Air, compressed.

• See SPECIAL PRECAUTIONS.

EQUIPMENT:

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

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

SAMPLING:

1. Calibrate each personal sampling pump with a representative sampler in line.
2. 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.

SAMPLE PREPARATION:

3. 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.
4. Add 5 mL ashing acid and cover with a watchglass.
5. Heat on hotplate (140 °C) until the solution is colorless.
6. Add 1 mL conc. HNO 3 and/or 70% HClO 4 drop by drop as needed to complete the ashing.
7. Remove the watchglass.
8. Heat on 140 °C hotplate until dense SO 3 fumes appear.
9. Allow the mixture to cool.
10. Transfer the solution quantitatively to a 25-mL volumetric flask.
11. Dilute to volume with distilled or deionized water.

CALIBRATION AND QUALITY CONTROL:

12. 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.