Page:NIOSH Manual of Analytical Methods - 7701.pdf/3
LEAD by ULTRASONIC EXTRACTION/ASV: METHOD 7701, Issue 2, dated 15 March 2003 - Page 3 of 4 CALIBRATION AND QUALITY CONTRO L: 7. Prior to field work, prepare a series of working standards covering the range 0.25 to 20 :g/mL Pb. a. Add aliquots of calibration stock solution to 100-mL volumetric flasks, and dilute to volume with 10% HNO 3. Sto re and transport the working sta ndards in polyeth ylene bottle s, a nd pre pare fresh week ly. b. Analyze the working standard s together with the blanks and sam ples (steps 11 through 14). c. Prepare a calibration graph of instrumental response vs. lead concentration (:g/m L Pb). NOTE: Some portable instruments read concentration d irectly. Calibrate acco rding to manufacturer’s directions. 8. Analyze at least one stan dard for every 20 sam ples to check for instrumen t drift (steps 11 through 14). 9. Check recoveries with at least one spiked media blank per 20 samples (one per batch minimum ). Use certified reference materials to substantiate recoveries. Use method of standard additions to check for matrix effects or interferences. 10. Check for lead contamination by analyzing at least one reagent and one media blank per 20 samples (m inimum of one per ba tch)(steps 11 through 14).
MEASUREMENT: 11. Set instrument parameters as specified by the manufacturer, or use conditions specified on page 7701-1. NOTE: If renewable electrodes are used, clean the glassy carbo n electrode and de posit a fresh m ercury film prior to conducting analyses. 12. Transfer sample aliquot (1 to 5 mL) to analytical cell, and dilute with 10% HNO 3, if necessary. NOT E: High concentrations of lead may require analysis of diluted analyte solutions. 13. Add supporting electrolyte and oxygen scavenger to sample cell. Ensure final volume of the cell is 5 mL (disposable electrodes) or 10 m L (renewab le electrodes) by diluting with distilled or deionized water. 14. Me asu re lead co nten t of the sam ple aliqu ot (:g/sam ple or :g/m L), an d rec ord th e res ult. NOTE 1: For renewable electrodes, rinse and drain electrochemical sample cell at least three tim es w ith distilled or de ionized wate r betw een sam ple runs. For disposable electrodes, us e a fresh plastic sam ple cell container for each sample analyzed. NO TE 2: If the m eas ured value is abo ve the linear ra nge of the standard s, dilute w ith 10% HNO 3, reanalyze, and apply the appropriate dilution factor in the calculations.
CALCULATIONS: 15. Using measured lead contents, calculate the corresponding concentrations (:g/mL) of lead in the original extra cted sam ple, C s, and average m edia blank , C b, from the calibration graph. NOT E: Be sure to account for dilution factors. 16. Using solution volum es (m L) of the sam ples, V s, and m edia blank s, V b, calcu late the con cen tration, C (m g/m 3), of lead in the air volume sa m pled, V (L):
NO TE : :g/mL / m g/m 3
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition