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
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Comments
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| OSHA ID-142
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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).
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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.
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| 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.
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NIOSH 7501
[167 KB PDF]
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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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