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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

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