Determining the heterogeneity of reference materials
LE3 .A278 2015
Bachelor of Science
Earth & Environmental Sciences
A Certified Reference Materials (CRMs) is a pulverized geological material used by geoscientists to assess analytical quality because it has accepted values for its element concentrations and its associated variabilities. The geoscientist can analyze these CRMs and compare the measured concentration to the accepted concentration and variance to determine the accuracy and precision of their analyses. Unfortunately, CRMs exhibit errors that depend on sample mass. As a result, CRMs provide only limited information about data quality from their measured and accepted concentrations. CRMs are commonly provided with a statistic that describes the variation in element concentration: the accepted standard deviations. These are calculated from the results of an inter-laboratory analysis of replicate samples. Unfortunately the accepted standard deviation does not describe only the heterogeneity of the sample. Rather, they describes the combined sampling error and analytical error. Furthermore, the sampling error is dependent on the sample mass, causing the measured error for some methods to differ substantially from the accepted error. These limitations are inescapable if the accepted standard deviation is used, as is the common practice. A method has been applied in this study to determine the heterogeneity of a representative suite of CRMs. This method can be applied by geoscientists to rectify some of the limitations of current practice resulting from the assumption that CRMs have no sampling error. This study measures the relative magnitudes of sampling and analytical error in CRMs, and recommends future research that will develop appropriate data quality assessment methods that accommodate the existence of CRM heterogeneity.
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