Substrate standard absorption correction

Table I lists several XRD analytical methods recently developed in the NIOSH laboratories. For each analyte, the analytical range, detection limit and analytical precision are listed. The method numbers refer to the NIOSH Manual of Analytical Methods (2.). As indicated in the table, there are several NIOSH methods available for free silica analysis. Method No, P CAM 109 incorporates the internal standard approach as developed by Bumsted (3.), The other two methods S-315 and P CAM 259 are based on the substrate standard method. The major difference between the two is the direct sampling on silver membrane filters (S-315). This paper will address the various methods of quantitation, sample collection and procedures for matrix absorption corrections that have been used in this laboratory for the analysis of crystalline particulate contaminants in the workplace.

Proponents of the internal standard procedure have questioned the validity of the substrate standard method to adequately correct for matrix absorption, Leroux and coworkers JLA) have presented data which support the method in addition, several measurements were performed in this laboratory to verify the validity of the method ( ), Mixtures of chrysotile in talc (1-7%) were prepared and various quantities "spiked" on silver filters. Table III illustrates the results obtained after correcting for matrix absorption as compared with the uncorrected data. Overall, there is excellent agreement between the corrected weight and the "spiked" weight. 

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