Bulk analysis of columbite ores by LA-ICP-MS: development of reference materials and investigation into matrix effects

Determination of metal elements in columbite ores is of great importance in understanding the potential economic significance and the origin of deposits. LA-ICP-MS is recognized as a green and efficient method for the bulk analysis of trace elements in natural samples. However, a major issue is the lack of matrix-matched reference materials for columbite ores. In this study, we developed an advanced method to produce pressed ultrafine-powder pellets with appropriate concentrations by applying a wet-mill method. The optimized scheme achieves a typical grain size of d90 = 1.74 mu m, forming pressed powder pellets with great cohesion and homogeneity, suitable for LA-ICP-MS. The relative standard deviation (RSD) values obtained from repeated measurements are <10% for more than 50 elements, comparable to those of homogeneous reference glasses. A systematic investigation of glass reference materials, commercial iron ore pellets, and our synthetic columbite ore pellets revealed significant matrix effects in various materials when using nanosecond laser ablation. Although the use of a femtosecond laser ablation system can partially suppress the matrix effect that occurs during the laser ablation process, the matrix effect in the ICP caused by differences in chemical composition remains challenging to resolve. The use of a "wet" plasma mode enhanced the matrix effect. Our results highlight the importance of matrix-matched reference materials in quantitative analysis of columbite ores and other ore samples. Utilizing the matrix-matched calibration method, we successfully determined trace elements in pressed powder pellets of iron ore (MAKR-NP) and columbite ore (LSC), with discrepancies of less than 10% for most elements.