A multi-point calibration method for electron probe microanalysis (EPMA) of indium in sphalerite (ZnS)

This article presents a multi-point calibration approach for electron probe microanalysis (EPMA) for the trace element analysis of indium in sphalerite (ZnS). To define a multi-point calibration curve, indium and cadmium-doped ZnS crystals in a concentration range from 0 (blank) to ~ 1500 µg / g were used. The samples were measured with two different analytical settings (25 kV acceleration voltage and 100 nA beam current as well as 7 kV and 200 nA). The figures of merit including, beam stability, lower limit of detection and limit of quantification as well as the reproducibility and precision are assessed. Equally, the line overlap of Cd and chemical shift due to non-matrix matched standards is discussed. The multi-point calibration approach results in a 2-3 times improved analytical precision compared to the classical calibration approach using only one calibration sample, and detection limits down to about 20 µg / g were achieved.