Effect of Sample Injection Volume on Non-Spectroscopic and Spectroscopic Interferences in Inductively Coupled Plasma Mass Spectrometry

Abstract

Non-spectroscopic (also called matrix effects) and spectroscopic interferences (in particular, from oxide and doubly-charged ions) may compromise the accuracy of inductively coupled plasma mass spectrometry measurements. Dilution is widely used to reduce the matrix effects that depend on the absolute quantity of matrix. However, dilution is a source of errors (especially when performed manually) and takes considerable time. An alternative method of reducing the absolute quantity of matrix is proposed in this article, through a reduction in sample injection volume. In this study, capillary-based mono-segmented flow analysis (MSFA) with sample injection as small as 1 µL was compared to the continuous nebulization of sample solutions and flow injection of 50-µL aliquots. The injection volume and oxide interference had a positive correlation, with 1-µL MSFA reducing the amount of CeO+/Ce+ by up to 69%. The concurrent increase in Ba++/Ba+ as the sample volume decreased suggests an increase in plasma temperature when smaller sample volumes are introduced. Signal suppression induced by the 400-mg L-1 Na matrix significantly decreased as the volume of the injected sample decreased and was virtually eliminated with 1-µL MSFA. This decrease translated into a negative correlation between the sample volume and accuracy when a drinking water-certified reference material was analyzed by external calibration without internal standardization or matrix matching. Only 1-µL MSFA yielded concentrations within the range of inclusion for all analytes.