Determination of minor and trace elements in obsidian rock samples and archaeological artifacts by laser ablation inductively coupled plasma mass spectrometry using synthetic obsidian standards

Accuracy and repeatability of analytical results obtained by laser ablation (LA) inductively coupled plasma mass spectrometry (ICP-MS) critically depe nds on the availability of calibration standards, which should ideally have a matrix composition very close to the samples being analyzed. The prepara tion of synthetic obsidian standards (SOS) is described in this work, their minor and trace element composition (> 40 elements), determined by solutio n nebulization [CP-MS and inductively coupled plasma optical emission spect rometry is presented and their performance in the quantitative and semiquan titative analysis of obsidians by LA-ICP-MS is discussed. Due to matrix mat ching of SOS and natural obsidians, internal standardization of the analyte intensities by Al-27 or Si-29 had no significant effect on the final resul ts. Good analytical curves (r(2) > 0.995) were obtained with the SOS series , permitting quantitative determination of a large number of trace elements in geological and archaeological samples with repeatabilities typically be tween 5 and 10% and adequate accuracies, as shown by the generally good agr eement between solution nebulization and laser ablation data for the same s amples. Results obtained in the fast semiquantitative mode of calibration w ere in most cases statistically not different from those obtained by the qu antitative mode. This, for the routine analysis of a large number of sample s attractive feature, was achieved by the use of 47 quantified elements in SOS for updating of the response factors. An example for the application of analytical methodologies introduced in this work is shown in provenance st udies of archaeological obsidian artifacts from Ecuador. (C) 2001 Elsevier Science B.V. All rights reserved.