Page:NIOSH Manual of Analytical Methods - 7505.pdf/4

 LEAD SULFIDE: METHOD 7505, Issue 2, dated 15 August 1994 - Page 4 of 7 MEASUREMENT: 10.

Obtain a qualitative X-ray diffraction scan (e.g., 10 to 80° 2 Θ) of the settled dust sample or high-volume respirable sample to determine the presence of lead sulfide and any matrix interference (see APPENDIX). If quantitative analysis is to be performed on the field sample (percent PbS), wet-sieve it through a 10-µm sieve in order to match the particle size of the standards. The expected diffraction peaks are: Peak (2Θ Degrees) Primary Secondary Lead Sulfide Silver

11.

30.10° 38.12°

25.98° 44.28°

Mount the filter (sample, standard or blank) in the XRD instrument and: a. Determine the net intensity, I r, of the reference specimen before each filter is scanned. Select a convenient normalization scale factor, N, which is approximately equivalent to the net count for the reference specimen peak and use this value of N for all analyses. b. Measure the diffraction peak area of the most intense interference-free diffraction peak of PbS. Scan times must be long, e.g., 15 min. c. Measure the background on each side of the peak for one-half the time used for peak scanning. Add the counts from each side to obtain a total (average) background. Determine the position of the background for each sample. d. Calculate the net intensity, I x (the difference between the peak integrated count and the total background count). e. Calculate the normalized intensity, Î x, for the sample peak on each sample, field blank and standard:

f.

g.

NOTE: 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. These analyses serve only to verify that contamination of the filters has not occurred. The analyte peak should be absent. The normalized intensity of the silver peak should match that of the media blanks.

CALCULATIONS: 12.

Calculate the concentration of lead sulfide, C (mg/m

3

), in the air volume sampled, V (L):

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94