Quantitative Determination of Impurities in Solids by Mass Spectrometry

Abstract

The reliability of quantitative impurity analysis of solids by spark-source mass spectrometry has been improved as a result of recent investigations. In the past, the technique has been highly successful for quantitative estimation of extremely low impurity levels and for direct comparison of impurity levels in two similar materials. However, improvements in reproducibility and the establishment of reliable relative-sensitivity factors were required for accurate determination of absolute concentrations. It has now been shown that the ion-accelerating voltage and the level of rf spark excitation can have marked effects on relative-sensitivity factors. It is, therefore, extremely important to maintain these parameters constant. The influence of sample inhomogeneity on reproducibility has also been investigated, and here the very low sample consumption of the rf spark can be a disadvantage. The alternative method of excitation by low-voltage dc arc can be less affected by inhomogeneity because a larger amount of sample is involved in an analysis. Following the improvements in reliability of relative-sensitivity measurements, more systematic determinations of these factors have been carried out. It is shown that, when these correction factors are applied, quantitative accuracy of the order of 10% is achieved.