Analysis of Geochemical Samples by Microwave Plasma-AES

Accurate and reliable analytical techniques and methodologies possessing high sensitivity and selectivity, coupled with convenience and economy and applicable to real-world situations, are required for geochemical studies. Quantitative analysis of major, minor, and some trace elements were performed in several geochemical reference samples using a new microwave plasma-atomic emission spectrometry (MP-AES) technique. A range of rock, soil, sediment, and water reference materials were chosen to evaluate the performance of this technique. A set of sample decomposition/digestion methods, which included a closed digestion technique utilizing a multi-acid mixture in a closed vessel and a fusion digestion technique utilizing lithium meta-borate in a glassy carbon crucible, were used for the determination of all major and minor elements in addition to Si, and more than 15 trace elements in sample solutions at the ng/g and sub-ng/g levels. Matrix interference effects encountered from concomitant elements, acid type and concentration, calibration strategies adopted, detection limits, accuracy and precision obtained were discussed. The analytical wavelengths selected were based on sensitivity and interference effects from other concomitant elements present in different sample solutions. The detection limits for several elements were found to be in the 0.05 to 5 ng/g range, which approached those of an ICP-AES technique but were much superior to flame AAS. Precisions of <= 3% RSD were obtained for major and minor elements and <= 6% RSD for trace elements with comparable accuracies for most determinations. The results obtained in this study clearly indicate that MP-AES is a suitable atomic emission spectrometry technique for the accurate determination of major, minor, and selected trace elements required in geochemical studies.