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PARTICULATE FLUORIDES and HYDROFLUORIC ACID: METHOD 7906, Issue 2, dated 20 May 2014 - Page 2 of 6

OTHER METHODS: This method updates NIOSH 7906 [7] by providing full method accuracy information, and specifies the use of an impregnated filter instead of a treated cellulose pad. The procedure, which is consistent with ISO 21438-3 [6], replaces NIOSH 7903 [8] for the determination of particulate fluorides and gaseous HF in workplace air samples. The advantages of this method are that it can allow for the collection of the inhalable fraction of particulate fluorides by means of the pre-filter (housed within an optional inhalable sampler) and it can provide for lower limits of detection and quantitation for gaseous HF due to higher sampling flow rates. NIOSH 7902 [9] and ASTM D4765 [10] are alternative methods that are recommended for insoluble fluorides, which rely on detection of F- by ion-selective electrode. REAGENTS:

EQUIPMENT:

1. Water, deionized (DI), ≥18 MΩ-cm resistivity 2. Sodium carbonate (Na2CO3), anhydrous, American Chemical Society (ACS) analytical grade 3. Sodium hydrogen carbonate (NaHCO3), ACS analytical grade 4. Filter impregnation solution (0.75 M Na2CO3); Dissolve 7.95 g Na2CO3 in deionized water and swirl to mix. Then bring to 100 mL in a volumetric flask, stopper and mix thoroughly. 5. Eluent stock solution: 0.8 M Na2CO3 / 0.1 M NaHCO3; Dissolve 16.96 g Na2CO3 and 1.68 g NaHCO3 in deionized water and swirl to mix. Then bring to 200 mL in a volumetric flask, stopper and mix thoroughly. 6. Eluent solution: 8 mM Na2CO3 / 1 mM NaHCO3; Transfer 10 mL of 0.8 M Na2CO3 / 0.1 M NaHCO3stock solution to a 1 Liter volumetric flask, dilute to the mark with deionized water, stopper and mix thoroughly. Prepare fresh eluent solution weekly. 7. Fluoride (F-) standard solution, 1000 mg/L 8. Calibration stock solution, 100 mg/mL (as the anion): Place a 10 mL aliquot of fluoride standard solution into a 100 mL volumetric flask, dilute to the mark and mix thoroughly. The solution is stable for at least 4 weeks at room temperature. 9. To prepare the impregnated filter, evenly distribute 120 µL 0.75 M Na2CO3 over the surface of the filter and allow to dry at room temperature for several hours.

  • See Special Precautions

1. Sampler: 37-mm diameter cellulose nitrate pre-filter, 0.8 µm pore size, 37-mm impregnated cellulose nitrate filter. The untreated filter collects particulate fluorides, while the impregnated filter collects HF vapor. Arrange the filters serially (with the pre-filter upstream of the impregnated filter) in a 37-mm diameter 3-piece chemically inert cassette filter holder. 2. Personal sampling pump, 1 to 2 L/min, with flexible connecting tubing 3. Ion chromatograph (IC), with pre-column (50 mm by 4.0 mm), anion-exchange column (200 mm by 4.0 mm), suppressor column (4 mm) and conductivity detector; and connected to data processing unit 4. Ultrasonic bath 5. Vessels, 10-mL, inert plastic, with screw caps 6. Volumetric flasks, 25- to 1000 mL 7. Pipets, 50- to 10000 µL 8. Beakers, 25- to 100 mL 9. Filtration apparatus, with filter funnel 10. Disposable filters, cellulosic, 0.45 µm pore size 11. Styrene-based sulfonic acid resin cartridges 12. Water purification system, to prepare greater than or equal to 18 MΩ-cm resistivity deionized water 13. Bottles, polyethylene, 100 mL 14. Syringes, plastic, 5 mL and/or 10 mL 15. Syringe filter cartridges, with 0.8-µm pore size polytetrafluoroethylene (PTFE) membrane filters 16. Micro-syringes, 50 µL, with 60 mm x 0.6 mm needles 17. Auto-sampler vials, polypropylene, 0.75 mL capacity.

NIOSH Manual of Analytical Methods (NMAM), Fifth Edition

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