FLUORIDES, aerosol and gas by ISE F
MW: 18.998
CAS: (HF) 7664-39-3
METHOD: 7902, Issue 2
RTECS: (HF) MW7875000
EVALUATION: PARTIAL
OSHA : 2.5 mg/m 3 (fluorides); 3 ppm (HF) NIOSH: 2.5 mg/m 3 (fluorides); 3 ppm (HF); STEL 6 ppm (HF) ACGIH: 2.5 mg/m 3 (fluorides); C 3 ppm (HF) (1 ppm HF = 0.818 mg/m 3 @ NTP)
7902
PROPERTIES:
Issue 1: 15 February 1984 Issue 2: 15 August 1994
HF: liquid; BP 19.5 °C; fluoride salts liberate HF in presence of acids
SYNONYMS: sodium fluoride (CAS #7681-49-4); hydrogen fluoride; hydrofluoric acid; cryolite; sodium hexafluoroaluminate (CAS
- 13775-53-6).
SAMPLING SAMPLER:
MEASUREMENT
FILTER + TREATED PAD (0.8-µm cellulose ester membrane + Na 2CO 3-treated cellulose pad)
TECHNIQUE:
ION-SPECIFIC ELECTRODE
ANALYTE:
fluoride ion (F )
FLOW RATE:
1 to 2 L/min
FILTER (particulate F ):
VOL-MIN: -MAX:
12 L @ 2.5 mg/m 3 800 L
SHIPMENT:
routine
SAMPLE STABILITY:
stable
BLANKS:
2 to 10 field blanks per set
fuse in NaOH, dissolve in 50 mL water + TISAB
TREATED FILTER (gaseous F ):
extract in 50 mL water + TISAB
CALIBRATION:
standard F
RANGE:
0.03 to 1.2 mg F
ESTIMATED LOD:
3 µg F
PRECISION (Sr):
0.017 @ 55 to 220 µg per sample [2]
solutions in TISAB per sample
per sample [1]
ACCURACY RANGE STUDIED:
not studied
BIAS:
not determined
ˆ ): OVERALL PRECISION (S rT ACCURACY:
not determined not determined
APPLICABILITY: The working range is 0.12 to 8 mg/m 3 for a 250-L air sample. The method applies to mining samples, and samples from the aluminum reduction, ceramic, glass etching, electroplating, semi-conductor, and fluorochemical industri es. If other aerosols are present, gaseous fluoride may be underestimated owing to sorption on collected particles, with concur rent overestimation of particulate/gaseous fluoride ratio [3-8].
INTERFERENCES: In samples containing cryolite, aluminum is sufficiently concentrated to give erroneous fluoride concentrations [3]. Hydroxide ion greater than 1/10 of the fluoride level will interfere positively. Fe 3+ , Si4+ , and Al 3+ give a negative interference. Concentrations >8 µg/mL of these elements cannot be suppressed [9]. The TISAB suppresses up to 500 µg/mL Fe 3+ and up to 90 µg/mL Si 4+ .
OTHER METHODS: This revises method 7902 [10] which was withdrawn on 5/15/89. The method was originally based on a method by Elfers and Decker [11], and NIOSH method S176 for HF [2]. Method 7903 (Acids, Inorganic) is an alternative met hod for HF. Method 7906 (Fluorides by IC) employs the same sampling procedure, but uses ion chromatography for measurement.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94 FLUORIDES, aerosol and gas by ISE: METHOD 7902, Issue 2, dated 15 August 1994 - Page 2 of 4 REAGENTS: 1. 2. 3. 4. 5. 6. 7. 8. 9.
10.
11.
12.
EQUIPMENT:
Sodium carbonate (Na 2CO 3). Glycerol. Potassium chloride (KCl). Sodium acetate (NaC 2H3O 2·3H 2O). Cyclohexylene diamine tetraacetic acid (CDTA). Hydrochloric acid, 1:1 (v/v). Sodium fluoride (NaF).* Deionized water. Fixative solution. Dissolve 25 g Na 2CO 3 in deionized water. Add 20 mL glycerol. Dilute to 1 L. Total ionic strength activity buffer (TISAB), pH 5.5. Dissolve 37 g KCl, 68 g sodium acetate and 36 g CDTA in H 2O. Adjust to pH 5.5 ± 0.2 with 1:1 HCl. Dilute to 1 L. Calibration stock solution, 100 µg/mL: Dissolve 0.2211 g NaF (dried at 105 °C for 2 h) in deionized water; dilute to 1 L. Sodium hydroxide, 20% (w/v). Dissolve 200 g NaOH in deionized water to make 1 L solution.
See SPECIAL PRECAUTIONS.
SPECIAL PRECAUTIONS: Fluorides are extremely corrosive to skin, eyes and mucous membranes [12]. Perform all fusions in fume hood.
SAMPLING: 1. 2. 3.
1. Sampler: cellulose ester membrane filter, 37mm, 0.8-µm pore size, with porous plastic backup pad (Nuclepore #220800, or equivalent), treated cellulose pad (Moisten with 0.8 mL fixative solution and dry at 105 °C for 30 to 45 minutes. Discard if charred.) in a 3-piece cassette with a 1/2" extension. Assembly of sampler: Place treated pad in rear (outlet) piece of cassette, insert 1/2-inch extension, place porous plastic pad and membrane filter in upper part of extension, and insert top piece (inlet) of cassette. Press tightly together and seal with shrink band or tape. NOTE: Leak test with hand vacuum pump. 2. Personal sampling pump, 1 to 2 L/min, with flexible connecting tubing. 3. Crucibles, nickel, zirconium, or Inconel, 20- or 30-mL. 4. Bunsen or Meaker burner. 5. Tripod. 6. Triangle, ceramic-covered. 7. Volumetric flasks, 50- and 100-mL, and 1-L. 8. Pipets, appropriate sizes for standards. 9. Beakers, plastic, 100-mL or 150-mL. 10. Magnetic stirrer. 11. PTFE-coated stirring bars. 12. Fluoride ion selective electrode (ISE), NaF combination or with calomel-type reference electrode. 13. pH/ion meter with millivolt readout and pH electrode. 14. Hand vacuum pump.
Calibrate each personal sampling pump with a representative sampler in line. Sample at an accurately known flow rate between 1 and 2 L/min for a total sample size of 12 to 800 L. Do not exceed 2 mg total dust loading on the filter. Pack securely for shipment.
SAMPLE PREPARATION: 4.
Cellulose ester membrane filter (particulate fluoride). NOTE: Water-soluble particulate fluorides may be extracted by the procedure for gaseous fluorides. Insoluble particles require fusion. a. Transfer the membrane filter to a crucible containing 5 mL 20% NaOH. b. Evaporate to dryness. c. Heat residue to fusion temperature, 1 to 2 min, cool and dissolve in ca. 5 mL deionized water. NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94 FLUORIDES, aerosol and gas by ISE: METHOD 7902, Issue 2, dated 15 August 1994 - Page 3 of 4
5.
d. Transfer sample into 100-mL plastic beakers. e. Rinse crucible with 25 mL of TISAB then with a few drops of 1:1 HCl. f. Adjust to pH 5.5 ± 0.2 using 1:1 HCl. g. Transfer to 50 mL volumetric flask; dilute to volume with deionized water. Treated pad (gaseous fluoride). a. Transfer treated pads to 100-mL plastic beakers. b. Add 25 mL TISAB and 25 mL deionized water. c. Soak pad for 30 min with sufficient stirring to reduce it to pulp.
CALIBRATION AND QUALITY CONTROL: 6.
Calibrate daily with at least six working standards over the range 3 to 1200 µg F per sample. a. Add known amounts of calibration stock solution to 25 mL TISAB and 5 mL 20% NaOH (particulate fluoride) or 25 mL TISAB (gaseous fluoride) in 100-mL beakers. b. Adjust pH to 5.5 ± 0.2 with 1:1 HCl. c. Transfer to 50-mL volumetric flasks. Dilute to the mark with deionized water. NOTE: Working standards are stable at least one month in polyethylene bottles at 4 °C. d. Analyze together with samples and blanks (steps 7 through 10). e. Prepare separate calibration graphs (mV vs. log F concentration) for particulate and gaseous fluorides. NOTE: Calibration curve is not linear below 0.1 µg/mL or above 25 µg/mL.
MEASUREMENT: 7.
8. 9. 10.
Bring sample and standard solutions to room temperature. NOTE: Samples and standards must be at same temperature (within ± 2 °C) for accurate results. Pour ca. 20 mL of each solution into plastic beakers. Add magnetic stir bar, insert electrodes and gently stir on magnetic stirrer. Record potential (mV) after 2 min. NOTE: If measured concentration of F - is >25 µg/mL, dilute with appropriate matrix (step 6), reanalyze and apply dilution factor in calculations.
CALCULATIONS: 11.
12.
Using the proper calibration graph (particulate or gaseous), convert potential (mV) to solution fluoride concentration, C s (µg/mL), in the sample solution volume, V s (mL), and the average media blank, C b, in the blank solution volume, V b (mL). Calculate the concentration of fluoride, C (mg/m 3), in the air volume sampled, V (L):
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94 FLUORIDES, aerosol and gas by ISE: METHOD 7902, Issue 2, dated 15 August 1994 - Page 4 of 4 EVALUATION OF METHOD: Measurement precision, Sr, in the range 0.055 to 0.22 mg HF per sample averaged 0.017 with average recovery 100.0% [2]. Analytical results on field samples report detection limits of 3 µg per sample for both gaseous and particulate fluorides [1]. Reported collection ranges for gaseous fluoride and particulate fluorides were 4 to 61 µg per sample and 4 to 410 µg per sample, respectively [10].
REFERENCES: [1] UBTL Reports, NIOSH/DPSE Analytical Sequence Nos. #2454, 2703, 3117 and 3366. Measurement Research Support Branch, NIOSH (unpublished). [2] Documentation of the NIOSH Validation Tests, S176, U.S. Department of Health, Education, and Welfare, Publ. (NIOSH) 77-185 (1977). [3] Ibid, P&CAM 117. [4] Jahr, J. A New Dual Filter Method for Separate Determination of Hydrogen Fluoride and Dustlike Fluorides in the Air. Staub-Reinhalt. der Luft, 32(6) 17 (1972). [5] Israel, G.W. Evaluation and Comparison of Three Atmospheric Fluoride Monitors under Field Conditions. Atmos. Environment , 8, 159 (1974). [6] Pack, M.R., A.C. Hill, and G.M. Benedict. Sampling Atmospheric Fluorides with glass Fiber Filters. J. Air Pollution Control Assoc., 13 (8), 374 (1963). [7] Einfeld, W. Investigation of a Dual Filter Sampling Method for the Separate Estimation of Gaseous and Particulate Fluorides in Air. Thesis (M.S., Public Health), Univ. of Washington (1977). [8] Einfeld, W. and S.W. Hoestmann. Investigation of a Dual Filter Sampling Method for the Gaseous and Particulate Fluorides. Am. Ind. Hyg. Assoc. J. 40(7), 626 (1979). [9] Abell, M. T. Evaluation of Methods for Fluorides, Internal Technical Report, NIOSH, DPSE (1975). [10] NIOSH Manual of Analytical Methods, 3rd ed., Method No. 7902 (Fluorides, Aerosol and Gas), Vol. I (1984). [11] Elfers, L.A. and C.E.Decker. Determination of Fluoride in Air and Stack Gas Samples by Use of an Ion Specific Electrode. Anal. Chem. 40, 1658 (1968). [12] NIOSH/OSHA Occupational Health Guidelines for Chemical Hazards, U.S. Department of Health and Human Services Publ. (NIOSH) 81-123 (1981), available as GPO Stock #17-033-00337-8 from Superintendent of Documents, Washington, DC 20402.
METHOD REVISED BY: Charles Lorberau, NIOSH/DPSE.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94