Publisher © Czech Geological Survey, ISSN: 2336-5757 (online), 0514-8057 (print)
Evaluation of SiO2, Na2O, MgO, K2O determinations in silicate samples by z-score obtained from nineteen interlaboratory tests
Abstract
The accuracy of determination of SiO2, Na2O, MgO and K2O in rocks was evaluated using z-score from interlaboratory test GeoPT. The target standard deviation used for calculating z-score value is Ha = 0.02 • c08495. The interlaboratory samples were processed by standard methods used in Central laboratory. The z-score for SiO2, Na2O were found in demanded interval -2 < z < 2 (SiO2 19/19, Na2O 18/17-1 outlier corresponds to 0.02 absolute % Na2O). With MgO, K2O analyses, the situation is different. z-score of these analytes to be found within -2 < z <2, the concentration interval should be wider by 0.04 %. The examples of USGS reference materials AGV-2, BCR-2 and BHVO-2 demonstrate that concentration intervals of Central laboratory of the Czech Geological Survey correspond better with the values given in certificates. The explanation is that standard deviation Ha = 0.02.c°'8495 was chosen for all elements of periodic table and does not reflect element complexity of chemical separations. Matrix, element and sensitivity corrections can be adjusted in evaluation by coefficient k only (usually k = 0.02 in Ha). Nevertheless, studied methods give good results with the absence of systematic errors.
