Page:NIOSH Manual of Analytical Methods - 7082.pdf/3

 LEAD by Flame AAS: Method 7082, Issue 2, dated 15 August 1994 - Page 3 of 7 NOTE:

If the concentration (M) of any of the following is expected to exceed the lead concentration (M) by 10-fold or more, add 1 mL 1 M Na 2EDTA to each flask before dilution to volume: CO23, PO34 , I , F , CH3COO. If Ca2+ or SO24 are present in 2+ 10-fold or greater excess, make all standards and samples 1% (w/w) in La [3].

CALIBRATION AND QUALITY CONTROL: 11. Prepare a series of working standards covering the range 0.25 to 20 µg/mL Pb (2.5 to 200 µg Pb per sample). a. Add aliquots of calibration stock solution to 100-mL volumetric flasks. Dilute to volume with 10% HNO3. Store the working standards in polyethylene bottles and prepare fresh weekly. b. Analyze the working standards together with the blanks and samples (steps 14 and 15). c. Prepare a calibration graph of absorbance vs. solution concentration (µg/mL). 12. Aspirate a standard for every 10 samples to check for instrument drift. 13. Check recoveries with at least one spiked media blank per 10 samples. Use method of standard additions occasionally to check for interferences.

MEASUREMENT: 14. Set spectrophotometer as specified by the manufacturer and to conditions on page 7082-1. NOTE: An alternate wavelength is 217.0 nm [8]. 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. 15. Aspirate standards, samples, and blanks. Record absorbance readings. NOTE: If the absorbance values for the samples are above the linear range of the standards, dilute with 10% HNO3, reanalyze, and apply the appropriate dilution factor in the calculations.

CALCULATIONS: 16. 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. 17. 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

NOTE:

µg/mL

CsVs

CbVb V

, mg/m 3.

mg/m

EVALUATION OF METHOD: 3 Method S341 [9] was issued on October 24, 1975, and validated over the range 0.13 to 0.4 mg/m for a 180-L air sample, using generated atmospheres of lead nitrate [1]. Recovery in the range 18 to 72 µg Pb per sample was 98%, and collection efficiency of 0.8-m mixed cellulose ester filters (Millipore TypeAA) was 100% for the aerosols. Subsequent studies on analytical recovery of 200 µg Pb per sample gave the following results [2,4]:

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition