Page:NIOSH Manual of Analytical Methods - 7105.pdf/3

 LEAD by GFAAS: METHOD 7105, Issue 2, dated 15 August 1994 - Page 3 of 4 11. Check recoveries with at least one spiked media blank per 10 samples. NOTE: Perform a matrix spike of a sample occasionally to check for matrix interferences. If an adequate recovery is not obtained (85 to 115%), an alternate method of analysis should be used, such as flame AAS or ICP. MEASUREMENT: 12. Set spectrophotometer as specified by the manufacturer and to conditions on page 7105-1. NOTE: An alternate wavelength is 217.0 nm [3]. Analyses at 217.0 nm have slightly greater sensitivity, but poorer signal-to-noise ratio compared to 283.3 nm. Also, non-atomic absorption is significantly greater at 217.0 nm, making the use of D 2 or H2 continuum, or Zeeman background correction mandatory at that wavelength. 13. Add matrix modifier to samples and standards in proper ratio of 2 to 1 (sample or standard to matrix modifier). 14. Analyze standards, samples, and blanks. Record absorbance readings. NOTE: If the absorbance value for the sample is above the linear range of the standards, dilute with 5% HNO3, reanalyze, and apply the appropriate dilution factor in the calculations. CALCULATIONS: 15. Using the measured absorbances, calculate the corresponding concentrations (µg/mL) of lead in the sample, Cs, and average media blank, Cb, from the calibration graph. 16. Using the solution volumes (mL) of the sample, V s, and media blanks, Vb, calculate the concentration, C (mg/m3), of lead in the air volume sampled, V (L):

C

CsVs

CbVb V

, mg/m 3.

EVALUATION OF METHOD: Method P&CAM 214 [2], issued on 1/29/76, was based on a method for metal pollutants in water [4]. Air sampling and digestion procedures followthose in Method 7082. The analytical procedure was evaluated by DataChem Laboratories in 1990 [1]. The LOD was determined at 0.02 µg per sample, with a LOQ of 0.05 µg per sample. The precision of the measurement procedure was 0.049. The overall precision, bias, and accuracy of the method were not determined. The reagents for digesting various lead species are given below: Species

Digestion Method

Pb metal Pb metal Pb PbS PbO2 PbO2 Pb in paint* Pb in paint*

HNO3 only HNO3 + H2O2 HNO3 only HNO3 only HNO3 only HNO3 + H2O2 HNO3 only HNO3 + H2O2

Institute of Standards and Technology.
 * Standard Reference Material #1579, U.S. National

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition