Page:NIOSH Manual of Analytical Methods - 9000.pdf/4

 CHRYSOTILE ASBESTOS (BULK): METHOD 9000, Issue 2, dated 15 August 1994 - Page 4 of 6 NOTE: A large intercept indicates an error in determining the background, i.e., an incorrect baseline has been calculated or interference by another phase. Select six silver membrane filters as media blanks (for determination of sample self-absorption, step 13) randomly from the same box of filters to be used for depositing the samples. Mount each of the media blanks on the filtration apparatus and apply vacuum to draw 5 to 10 mL of 2-propanol through the filter. Remove, let dry and mount on sample holders. Determine the net

10.

normalized count for the silver peak, value for the six media blanks.

, for each media blank (step 12). Obtain an average

MEASUREMENT: 11.

Obtain a qualitative X-ray diffraction scan (e.g., 10 to 80 degrees 2-theta) of the sample to determine the presence of chrysotile and interferences. The expected diffraction peaks are as follows:

Mineral Chrysotile Silver 12.

Peak (2-Theta Degrees) Primary Secondary 12.08 38.12

24.38 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 a chrysotile peak that is free of interference. Scan times should 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. The sum of these two counts is the 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 and record the normalized intensity, Î x, for the sample peak on each sample 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; 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-theta range used for the analyte 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.

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