National Institute for Occupational Safety and Health

“ Normalizing to the reference specimen intensity compensates for long-term drift in X-ray tube intensity. If intensity measurements are stable, the reference specimen may be run less frequently and the net intensities should be normalized to the most recently measured reference intensity. Determine the net count, I Ag, of an interference-free silver peak on the sample filter following the same procedure. Use a short scan time for the silver peak (e.g., 5% of scan time for analyte peaks) throughout the method. Scan each field blank over the same 2- Θ range used for PbS and silver peaks. ”

“ R = sin ( ΘAg) /sin ( Θx) T = Î Ag/ (average Î Åg = transmittance of sample Î Ag = normalized silver peak intensity from sample average Î Ag = normalized silver peak intensity from media blanks (average of six values) NOTE: For a more detailed discussion of the absorption correction procedure, see references [4] and [5] .
EVALUATION OF METHOD: The measurement precision, Sr, initially determined with 30 samples in the range 30 to 2000 μg PbS per filter was 0.0047 [6] . ”

“ Correct Î ox for matrix absorption for standards containing more than 200 μg PbS (steps 11.f and 12) . g. Prepare a calibration graph by plotting Î ox vs. mass PbS (μg) . A weighted least squares (I/ σ2) fit is preferable. h. Determine the slope, m (counts/μg) , of the calibration graph. The intercept of the line should be zero ±5 μg. NIOSH Manual of Analytical Methods (NMAM) , Fourth Edition, 8/15/94 LEAD SULFIDE: METHOD 7505, Issue 2, dated 15 August 1994 - Page 4 of 7 MEASUREMENT: 10. ”