Studies into the interelement matrix effect in inductively coupled plasma spectrometry

Radially-resolved maps of calcium atom and ion emission and calcium atom and ion number densities have been obtained in the presence and absence of several concomitant elements. These concomitants include cesium, barium, lithium, aluminum, thallium, silver, magnesium and zinc. In addition, maps of electron concentration, electron temperature and gas-kinetic temperature are given for an analyte-only (Ca) plasma. The findings suggest the interelement interference effect to be the result of at least three major processes operating simultaneously: lateral-diffusion (i.e. particle-voratilization) changes, shifts in analyte-ionization equilibrium, and differences in collisional excitation efficiency. Expanded lateral diffusion caused by enhanced particle volatility explains the greater number of analyte species in the off-axis plasma zones when an interferent is added to the sample. The combined concomitant-induced effects of expanded lateral diffusion and shift in ionization equilibrium can be used to describe a drop in analyte ion concentration that occurs in the central channel but with little or no change in the Ca atom number density. Enhanced collisional excitation caused by small increases in the plasma electron number density and electron temperature result in elevated analyte emission intensities in some plasma zones. Also, a charge-transfer mechanism is described which might result in the direct production and excitation of Ca ions from molecular analyte species.