Page:NIOSH Manual of Analytical Methods - 7904.pdf/2

 CYANIDES, aerosol and gas: METHOD 7904, Issue 2, dated 15 August 1994 - Page 2 of 4 EQUIPMENT:

REAGENTS: 1. 2. 3.

4.

5. 6. 7. 8.

Deionized water. Potassium cyanide.* Calibration stock solution, 1000 µg/mL CN -. Dissolve 0.250 g KCN in 0.1 N KOH to make 100 mL solution. Stable for at least 1 week in polyethylene bottle. Potassium hydroxide (KOH), 0.1 N. Dissolve 5.6 g KOH in deionized water; dilute to 1000 mL. Lead acetate paper. Cadmium carbonate (if sulfide present). Hydrogen peroxide, 30% (if sulfide present). Sodium sulfite, 1 M (if sulfide present).



See SPECIAL PRECAUTIONS.

1. Sampler: polyvinyl chloride membrane filter, 37-mm diameter, 0.8-µm pore size in 2-piece filter cassette holder, followed by a glass midget bubbler containing 15 mL 0.1 N KOH. 2. Personal sampling pump, 0.5 to 1 L/min, with splashover protection and flexible connecting tubing. 3. Vials, polyethylene, with screw caps, 20-mL, and plastic tape for sealing. 4. Cyanide ion electrode, (Orion 94-06 or equivalent). 5. Reference electrode. 6. pH meter, readable to 0.1 mV. 7. Magnetic stirrer and stirring bars. 8. Jars, ointment, 60-mL, squat-form with aluminum-lined screw caps. 9. Pipets, 0.05- to 2 and 25-mL, with pipet bulb. 10. Volumetric flasks, 25-mL. 11. Beakers, 50-mL. 12. Analytical balance, readable to 0.1 mg.

SPECIAL PRECAUTIONS: Hydrogen cyanide gas and the cyanide particulates may be fatal if swallowed, inhaled or absorbed through the skin. Work in a hood. Amyl nitrite is the antidote for cyanide poisoning [7].

SAMPLING: 1. 2.

3. 4.

Calibrate each personal sampling pump with a representative sampler in line. Sample at 0.5 to 1 L/min for a total sample size of 10 to 180 L. NOTE: Maintain bubblers in a vertical position during sampling. Do not allow the solution level to fall below 10 mL. Remove the bubbler stem and tap it gently against the inside wall of the bubbler. Rinse the bubbler stem with 1 to 2 mL of unused 0.1 N KOH. Add the rinse to the bubbler. Quantitatively transfer the contents of the bubbler to a 20-mL vial. Close cap tightly and wrap with plastic tape to avoid sample loss during transit. Label each vial.

SAMPLE PREPARATION: 5. 6. 7.

Transfer the filter from the cassette filter holder to a 60-mL ointment jar. Pipet 25.0 mL 0.1 N KOH into the jar. Cap and allow to stand for at least 30 min with occasional shaking to complete extraction. Analyze within 2 h after extraction. Empty the contents of the vial into a 25-mL volumetric flask using 0.1 N KOH to rinse the vial. Add rinse to the volumetric flask. Dilute to the mark with 0.1 N KOH. NOTE: Sulfide ion irreversibly poisons the cyanide ion specific electrode and must be removed if present. Check for the presence of sulfide ion by touching a drop of sample to a piece of lead acetate paper; the paper will discolor in the presence of sulfide ion. If this test is positive, remove sulfide by one of the following methods: a. Add 1 mL 1 M H2O 2 and 1 mL 1 M Na 2SO 3 to sample solutions prior to diluting to volume. NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94