Flagging matrix effects and system drift in organic-solvent-based analysis by axial-viewing inductively coupled plasma-atomic emission spectrometry

Spatial emission maps across an end-on-viewed inductively coupled plasma were used to flag matrix interferences and system drift for organic-solvent-based samples. This method is based on the fact that a matrix interference affects emission signals differently from one cross-sectional location in the plasma to another. The method is straightforward: a set of calibration curves made with standard solutions is obtained at several cross-sectional locations in the plasma; each unknown sample is then analyzed by means of those curves. If a matrix interference exists, the determined concentration in the sample will appear to change from spatial location to another. Fundamentally, this behavior arises because the plasma is spatially heterogeneous and is affected by a sample matrix in a spatially dependent way. Isopropanol was used as the solvent for the determination of ten analytes (As, Cd, Co, Cu, Cr, Fe, Mg, Mn, Ni, and Zn). Three types of matrix interference were examined: spectral, plasma-related and sample-introduction-related. It was found possible to flag errors as small as 2% caused by any of the three types of matrix interference, as well as system drift.