A reliable calibration method for accurate determination of major and trace elements in fluorapatite by LA-ICP-MS without an internal standard

Abstract

During in situ determination of major and trace element concentrations of minerals by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), an internal standard is needed. In this study, we present a new modified calibration strategy without using an internal standard but still able to achieve accurate major and trace element determination of fluorapatite by LA-ICP-MS. Reference materials and normalization to bulk metal-oxide components as 100% were used to correct absolute amount differences of materials and sensitivity drift during each ablation process. Because F and P have high first ionization energy with low sensitivity in ICP-MS and may not be accurately measured by quadrupole ICP-MS, we determined the concentrations of these elements based on the calculation of the mineral unit formula to remove the disturbance of F and P to total normalization. We used the calibration with reference standards plus the above modified calibration strategy to determine the compositions of the standard reference material Durango and two types (magmatic and hydrothermal) of fluorapatite samples. The data of major and trace element compositions obtained by our new method without an internal standard are identical to those of the previous traditional internal standard-dependent calibration method within 1%. Overall, our new calibration method can achieve the same accuracy but lower cost and less time compared to the previous method.