TRACE-ELEMENT ANALYSIS OF NATURAL GOLD BY LASER-ABLATION ICP-MS - A COMBINED EXTERNAL INTERNAL STANDARDIZATION APPROACH/

For the trace element analysis of gold by laser ablation ICP-MS, exter nal calibration samples of differing matrix composition have been used in previous studies. Data presented here suggest that even for calibr ation samples and unknowns with closely-matched matrices, discrepancie s arise due to variations in the coupling behaviour of the laser with the sample at different power deliveries, and can lead to erroneous tr ace element determinations. Internal standardisation for gold is compl icated because Au and Ag, the most common major elements, do not have minor isotopes that can be used as internal standards. This problem wa s overcome for natural gold samples by using an external calibration s ample only for the major elements Au and Ag, then defocussing the ion path and using Ag-107 in each sample as an internal standard against w hich mu g g(-1) levels of Te, Sb, Hg, Bi, and Cu were determined. The results suggest that trace elements can occupy lattice sites in gold r ather than occurring only as micro-inclusions of other phases. The ana lytical approach taken here may be used in trace element analysis wher e adequate external calibration samples are not readily available.