Routine quantitative multi-element analysis of sulphide minerals by laser ablation ICP-MS: Standard development and consideration of matrix effects

Abstract

The paper describes a calibration standard for quantitative in-situ multi-element analysis of sulphide minerals by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Standard STDGL2b2 is a mixture of 25% Zn concentrate and 75% pyrrhotite doped with a number of additional trace elements and fused into an X-ray fluorescence (XRF) glass disk. The homogeneity of the disk has been tested for the 55 elements of interest. All elements except Se, Tl, Au and Pt are homogenous (< 5% variation). Accurate analysis for the above four elements requires averaging multiple analyses of the standard. Element concentrations in STDGL2b2 were quantified by XRF and standard solution ICP-MS using a Finnigan Element and an Agilent 4500 mass-spectrometers. For the analysis of pyrite, pyrrhotite, chalcopyrite, galena and sphalerite, analytical errors caused by matrix-dependent fractionation have been evaluated by analysing five pressed-powder pellets. The compositions of the powders have been analysed by XRF and solution ICP-MS. When Fe or Pb can be used as the internal standard, errors for most elements are < 15%, but reach up to 50% for W, Zn and Cd, requiring correction factors to be introduced. However, when Zn is used as the internal standard, significant correction factors are required for most elements. Comparison of the results obtained with two different laser microprobes, a solid state 213 nm and an excimer 193 nm, indicates that either is well suited for LA-ICP-MS analysis of sulphide minerals using STDGL2b2 as the calibration standard. Use of STDGL2b2 significantly improves accuracy of sulphide analysis by LA-ICP-MS compared to silicate reference materials, such as the NIST 600 series.