[Characterization of matrix effects in microanalysis of sulfide minerals by laser ablation-inductively coupled plasma-mass spectrometry based on an element pair method].

Matrix effect between reference materials and samples is one of the major factors affecting the accuracy of analytical results by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). However, there is no method or calculation formula to quantify matrix effect between standards and samples up to date. In this paper, the linear correlation coefficient r of the Ii/I(is-Ci)/Cis graphs of element pairs were used to characterize the matrix effect, which took the ratios of concentrations (ci/ c(is)) and intensities (Ii/Iis) of the analytical element and internal standard element as x-axis and gamma-axis, respectively. Matrix effects of 6 element pairs in 13 glass reference materials, 2 sulfide reference materials and 2 sulfide minerals using Fe as internal standard was studied, with the linear correlation coefficient r of Fe-Cu, Fe-Zn element pairs both less than 0. 999 and trace Fe--Mn, Fe--Co, Fe--Ga, Fe--Pb element pairs all better than 0.999. Matrix effects of 3 major element pairs in 2 sulfide ref- erence materials and 6 sulfide minerals using S as internal standard was also studied, with the linear correlation coefficient r of S--Fe, S--Cu, S--Zn all less than 0.999. The great majority of relative errors of EMPA analytical results for major elements in sulfide minerals were greater than 10%, whether analyzed using Fe as internal standard with glass reference materials as external standard, or S as internal standard with sulfide reference materials MASS-1, IMER-1 as external standard, respectively. But the most analytical results for trace elements calibrated by glass reference materials using Fe as internal standard were well agreed with sulfide standard MASS-1, with the relative errors less than 15%. The results showed that matrix effects existed in glass reference materials, sulfide reference materials and sulfide minerals, and it also proved a certain rationality and practicability for quantification of matrix effect using the linear correlation coefficient r of the Ii/Iis-Ci/Cis graphs by this element pair method. This study also indicated that trace elements in sulfide minerals could be calibrated using Fe as internal standard with non-matrix matched glass reference materials as external standard, especially for NIST610 contained nearly all the trace elements in sulfide minerals and with relative high concentrations of each element, which obtained analytical results agreed well with sulfide standard MASS-1.