National Institute for Occupational Safety and Health

“ Use a diffraction peak of high intensity that can be rapidly but reproducibly (S r <0.01) measured. b. Mount the sam ple, work ing standard, or blank filter. Measure the diffraction peak area for each silica po lymo rph. Scan times m ust be long, e.g., 15 min (longer scan times will lower the limit of detection) . c. Mea sure 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. ”

“ If intensity measurem ents are stable, the reference specimen m ay be run less frequently and the net intensities should be normalized to the most recently-measured reference inten sity. f. Determine the norm alized coun t, ÎAg, 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. g. Fie ld blanks may be analyzed by scanning the 2-theta range used for the analyte and silver peaks to verify that contam ination of the filters has not occu rred. ”

“ A high level of analyst expertise is required to optimize instrument parameters and correct for matrix interferences either during the sample preparation phase or the data ana lysis and interpretation pha se [15] . The analyst should have som e training (university or short course) in mineralogy or crystallography in order to have a background in crystal structure, diffraction patterns and mineral trans form ation. ”

“ Select six silver mem brane filters as media blanks randomly from the same box of filters to be used for depositing the samples. These will be used to test for sample self-absorption. Mount each of the m edia blanks on the filtration a ppa ratus and app ly vacuu m to draw 5 to 10 m L 2-propan ol through the filter. Rem ove, let dry, and mount on XRD holders. Determine the net normalized count for the silver peak, îAg, for ea ch m edia blank (step 12.g) . Ob tain an average value for the six m edia blank s, Î Aog. ”

“ NIOSH Manual of Analytical Methods (NMAM) , Fourth Edition SILICA, CR YST ALLINE , by XRD: M ETH OD 7500, Issue 4, dated 1 5 Ma rch 2003 - Page 5 of 9 c.
10.
Mount a silver filter on the filtration apparatus. Place several m L of 2-propano l on the filter. Turn off the stirrer an d sh ake vigorous ly by hand . Imm ediately rem ove the stopper and withdraw an aliquot from the center at half-height of the 10 mg/L or 50 mg/L suspension. Do not adjust the volume in the pipet by expelling part of the suspension. ”

“ U.S. Departm ent of He alth and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for O ccu pation al Safety and Health, DHHS (NIOSH) Publication No. ”