Page:NIOSH Manual of Analytical Methods - 7105.pdf/2

 LEAD by GFAAS: METHOD 7105, Issue 2, dated 15 August 1994 - Page 2 of 4 EQUIPMENT: REAGENTS: 1. Sampler: Cellulose ester membrane filter, 1. Nitric acid, conc.* 0.8-µm, 37-mm, in 2-piece cassette. 2. Nitric acid, 5% (v/v). Add 50 mL conc. HNO3 2. Personal sampling pump, 1 to 4 L/min, with to 500 mL water; dilute to 1 L. flexible connecting tubing. 3. Hydrogen peroxide, 30% H2O (w/w), reagent 3. Atomic absorption spectrophotometer with grade.* graphite furnace atomizer and background 4. Calibration stock solution, 1000 µg/mL Pb. correction. Commercial standard or dissolve 1.00 g Pb 4. Lead hollow cathode lamp or electrode metal in minimum volume of HNO3 and dilute dischargeless lamp. to 1 L with 1% (v/v) HNO3. Store in a 5. Regulators, two-stage, for Argon. polyethylene bottle. 6. Beakers, Phillips, 125-mL, or Griffin, 50-mL 5. Matrix Modifier. Place 0.2 g NH4H2PO4 and with watchglass covers.** 0.3 g Mg(NO3)2 in a 100-mL volumetric flask. 7. Volumetric flasks, 10- and 100-mL.** Add 2 mL conc. HNO3 and bring to volume 8. Assorted volumetric pipets as needed.** with distilled or deionized water. 9. Hotplate, surface temperature 140 C. 6. Argon, prepurified. 7. Distilled or deionized water. 10. Bottles, polyethylene, 100-mL.


 * See SPECIAL PRECAUTIONS.

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

SPECIAL PRECAUTIONS: Concentrated nitric acid is an irritant and may burn skin. Perform all acid digestions in a fume hood. Hydrogen peroxide is a strong oxidizing agent, a strong irritant, and corrosive to the skin. Wear gloves and eye protection.

SAMPLING: 1. Calibrate each personal sampling pump with a representative sampler in line. 2. Sample at an accurately known flow rate between 1 and 4 L/min for up to 8 h for a total sample size of 1 to 1500 L for TWA measurements. Do not exceed a filter loading of ca. 2 mg total dust. SAMPLE PREPARATION:

3. 4. 5. 6. 7. 8.

NOTE: Some matrices, especially bulk samples containing epoxy-based paint, may require a different digestion procedure for complete recovery of lead. See the Appendix of Method 7082 (Lead by Flame AAS) for a microwave digestion procedure which can be used for this purpose. Open the cassette filter holders and transfer the samples and blanks to clean beakers. Add 3 mL conc. HNO3, and 1 mL 30% H2O2 and cover with a watchglass. Start reagent blanks at this step. Heat on 140 C hotplate until volume is reduced to about 0.5 mL. Rinse the watchglass and walls of the beaker with 3 to 5 mL 5% HNO 3. Allow the solution to evaporate to 0.5 mL. Cool each beaker. Transfer the solution quantitatively to a 10-mL volumetric flask and dilute to volume with distilled water.

CALIBRATION AND QUALITY CONTROL: 9. Prepare a series of six working standards covering the range 0.002 to 0.1 µg/mL Pb (0.02 to 1.0 µg Pb per sample). a. Add aliquots of calibration stock solution to 100-mL volumetric flasks. Dilute to volume with 5% HNO3. Store the working standards in polyethylene bottles and prepare fresh weekly. b. Analyze the working standards together with the blanks and samples (steps 12 through 14). c. Prepare a calibration graph of absorbance vs. solution concentration (µg/mL). 10. Analyze a standard for every 10 samples to check for instrument drift. NIOSH Manual of Analytical Methods (NMAM), Fourth Edition