System for Automatic Selection of Operating Conditions for Inductively Coupled Plasma Atomic Emission Spectroscopy

Abstract

The design of a system for automatic parameter and methodology selection for inductively coupled plasma atomic emission spectroscopy (ICP-AES) is presented. The ICP is an excellent excitation source that suffers less from matrix effects than other sources but is not altogether problem-free. To compensate, a variety of methodologies and approaches can be used to minimize matrix-induced error present in an analysis. For example, one can prepare matrix-matched standards, use standard additions or select instrumental parameters (rf power, pump rate and viewing height) specifically for the analytes of interest. Ideally, an Autonomous Instrument, operating without human intervention, needs to have the ability to determine the analytical parameters and methodology to apply to a sample. A measure of expected analytical error for a sample to be used by an Autonomous Instrument, the total interference level (TIL), is introduced. The TIL applies the results from a semiquantitative scan to a ‘lookup’ table to determine what the approximate expected error will be. It relies on a ‘conservative’ approach and assumes the effect of interferences on a particular analyte are not only linear, but additive. This approach was applied to samples with high concentrations of interferents and works well, providing acceptable estimates in 90% of analyte–interferent combinations (at 10% error tolerance). The emphasis of the discussion is placed on how well this system deals with ‘problematic’ samples,i.e. those samples where matrix effects cause considerable analytical error.