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Less expensive alternative to XRD for certain matrices. More prone to interferences. Second-most common method. Method used by MSHA for analysis of respirable coal dust containing quartz.

Federal Agency


Methods
 
Comments
 
MSHA P-7 Applicable for the analysis of quartz in coal dust. Samples are ashed, mixed with KBr and pressed into a pellet for presentation in the instrument. Cristobalite, tridymite, amorphous silica, and many silicates in common minerals and glasses interfere in the IR analysis of quartz silica because they have common absorption bands. The clay silicate common to coal is accounted for and the effect of the interference is subtracted. Silicates are very common representing nearly 95% of the volume of the earth's crust. Applicability to non-coal matrices should be determined on a case-by-case basis. Muffle furnace ashing method may require acid pre-wash to remove CaCO3. Calls for use of NIST-traceable Standard Reference Material (SRM) or Min-U-Sil 5 (Pennsylvania Glass Sand Co., Berkley Springs, WV).
 
NIOSH 7602
[130 KB PDF]
Similar to MSHA P-7 and based on NIOSH P&CAM 110 with mixing of sample with KBr and pressing into a pellet for presentation in the instrument. Can be used to analyze quartz or cristobalite or tridymite or quartz-and-cristobalite. The latter mixture requires use of an alternate, less sensitive absorption band. Silicates can be removed using a phosphoric acid cleanup procedure. Calls for use of NIST-traceable Standard Reference Material (SRM).
 
NIOSH P&CAM 110 Similar to MSHA P-7. Earlier version of NIOSH 7602. Does not specify use of Standard Reference Material. Replaced by NIOSH 7602.
 
NIOSH 7603
[120 KB PDF]
Similar to MSHA P-7 with redeposit of the sample on a filter for presentation in the instrument. Calls for use of NIST-traceable Standard Reference Material (SRM). Infrared light scattering depends on the amount of respirable dust present (both crystalline silica and matrix) and may be stronger than when using a KBr pellet. Such scattering affects the baseline and may lead to non-linear response.



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