Quantitative analysis of silicates using LA-ICP-MS with liquid calibration

For more than a decade liquid calibration has been proposed and selectively applied as a calibration strategy for laser-generated aerosols. However, matrix independent calibration is not a well-accepted technique for quantification in direct solid analysis using LA-ICP-MS. In this study three synthetic calibration solutions were used for the analysis of three silicate reference materials (BCR-2G, ATHO, and NIST 610). The calibration solutions were introduced into the ICP using an Aridus liquid sample introduction system with aerosol desolvation, while argon was used as the carrier gas. A 193 nm ArF excimer laser ablation system generated sample aerosols using helium as carrier gas. The argon carrier gas containing the solution nebulization aerosols was mixed, using a sheath gas adaptor in front of the ICP, with the laser aerosol carried in helium. Two different calibration strategies were applied for the multielement quantification of three geological reference materials. The first calibration technique used internal standardization with Ca as the internal standard. The second approach used synthetic calibration solutions containing all major, minor, and trace elements, in which the concentration ratios and concentrations of the elements were known. A normalization algorithm was used which calculated the sum of all of the determined element concentrations as oxides to 100%. The data shown for Ca indicate that both procedures are well suited for multi-element determinations. The 100% oxide normalization strategy allowed the calculation of the Ca concentration based on the total matrix used as internal standard. This Ca concentration was then used for the determination of the trace element composition of the sample. The advantage of this calibration is the possibility of element analysis in silicates without knowing the element concentration of at least one internal standard element prior to analysis. However, this study also shows that the composition of the solution used for the calibration can lead to losses of some elements during the desolvation process in the Aridus or during aerosol transfer to the ICP, which will be shown for Cu.