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Most universal in applicability. Widely accepted in chemical industry. Most common method. Method used by OSHA Compliance and Consultation Labs. Used by the MSHA Lab for analyzing crystalline silica in respirable metals and non-metal mine dust.

Federal Agency


Methods
 
Comments
 
OSHA ID-142 Can distinguish and analyze the three different crystalline forms (polymorphs), quartz, cristobalite, and tridymite. Similar to NIOSH 7500. Uses routine analysis on additional analytical lines to resolve interferences and provide both qualitative and quantitative confirmations. Does not require bulk sample, although such samples may be included in an OSHA inspection. Analysis of bulk samples can serve to evidence that quartz is indeed present, or to support HAZCOM citations, and in rare instances assist in chemical removal of an interference. ID-142 does not incorporate absorption corrections, but rather uses multivariate calibration. Instrument is calibrated for three to four diffraction peaks for each polymorph. Uses integrated peak areas rather than peak height to account for variation in particle-size distribution in respirable air samples. Calibration uses transformation of variables to harmonize variance across entire analytical range. Calibration curve indicated is non-linear to model analytical effects of integration, shadowing, and absorption due to analyte. Also calls for use of NIST-traceable Standard Reference Material (SRM).

NIOSH 7500
[155 KB PDF]
Can distinguish and analyze the three different crystalline forms (polymorphs), quartz, cristobalite, and tridymite. The bulk sample is analyzed first in order to determine whether interferences are present, and if so, which alternative analytical line is most appropriate Because the analysis is based on only one analytical peak and therefore requires collection of a settled dust or high volume bulk sample representative of the air samples taken. Such bulks may be difficult to obtain or difficult to match analytically in terms of particle size. Uses absorption corrections to account for low recoveries in some matrices. Absorption corrections can over- or under- compensate. Calls for use of NIST-traceable Standard Reference Material (SRM) to prepare quartz are cristobalite standards. (NIOSH provides tridymite SRM.) Uses peak height. Calibration curve indicated is linear model statistically weighted according to variance. Linear curve does not take into account reduced sensitivity at low analyte levels.

NIOSH P&CAM 259 An early method which does not have a requirement for traceable Standard Reference Material. This method is the precursor to NIOSH 7500, and has been replaced by that method.
 
NIOSH 7501
[167 KB PDF]
Is used to analyze samples for amorphous silica. The sample is first analyzed for crystalline silica. Amorphous silica in the sample is then converted to cristobalite by heating in a muffle furnace. The sample is then reanalyzed for crystalline silica and the amorphous silica is calculated by difference. Sample collection and analysis procedures are similar to NIOSH 7500.



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