QUARTZ in coal mine dust: METHOD 7603, Issue 3, dated 15 March 2003 - Page 6 of 7 15.
16.
If correction for kaolinite is not required, use the absorbance at 800 cm ! 1 determined in step 12. Determine the weight of qu artz, W q (µg), from the quartz standard curve. Since the deposition area for samples and standards is the same, it is not necessary to correct for area. Ca lculate the percent quartz by dividing the weight of quartz, W q (µg), by the total sam ple weight, W s (µg).
EVALUATION OF METHOD: This method is based MSHA P-7 which was collaboratively tested [2,4]. The testing included a ruggedization step to test the effects of the use of muffle furnace or plasma asher, amount of calcite or kaolinite on the sample, ashing time, pH of solvent to remove calcite, shipment of samples and others. None of these factors was found to have an effect. Results obtained by this method are equivalent to those obtained by Method 7500. A collaborative study of the rugge dized m etho d wa s pe rform ed w ith 15 lab orato ries participa ting [2]. The total erro rs an d interlabora tory and intralabora tory errors were found to be dependent on the types of samples. For samples collected from laboratory-generated aerosols, using a set of matched-flow orifices, the lower and upper limits of the relative standard deviation over the range 60 to 150 µg quartz were:
Total error (RSD) Intralaboratory error Interlaboratory error
Lower
Upper
0.13 0.07 0.08
0.22 0.10 0.14
The lower limit applies to samples containing up to 1 mg coal mine dust with less than 2% kaolinite; the upper lim it was found for samples with 2 mg coal mine dust or a lower amount of coal mine dust with more than a few percent ka olinite. The total error increased to 0.36 to 0.40 (lower and upper range) when personal sampling pumps were used to collect the sam ples. The pum p error increased the interlaboratory error. Precision for pure quartz samples is ca. 0.05 in the 100 to 500 µg ra nge [4]. Precision fo r ac tua l sam ples is not as good and depends on sample size and ashing technique. This method is particle size dependent. The particle sizes of the standards and samples should be matched as closely as poss ible to prevent a bias in the res ults , wh ich is not c orrecta ble with this m etho d. A thorough study of the range of biases has not been done for IR methods.
REFERENCES: [1] [2]
[3]
[4]
Freedman RW , Toma SZ, Lang HW [19 74 ]. On -filter an alys is of q ua rtz in respirable coal dust by infrared absorption and X -ray diffraction. Am Ind H yg Assoc J 35:411. An de rso n C C [19 83 ]. Collaborative tests of two me thods for determining free silica in airborne du st. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Ce nters for Disease Con tro l, Na tiona l Institute for O ccu pa tiona l Sa fety a nd He alth, D H H S (NIOSH) Pub. No. 83-124. Key-Sch wartz RJ, Baron PA, Bartley DL, Rice FL, Schlecht PC [2003]. Chapter R, Determination of airborne crystalline silica. In: N IOS H M anu al of Analytical M etho ds, 4 th ed., 3 rd Suppl. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 2003-154. MSHA [1994]. Infrared dete rm ination of q uartz in res pirable coal mine dust: Method P-7. Pittsburgh, PA: U.S. Department of Labor, Mine Safety and Health Administration.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition
