It is well known that the emission intensities of different elements exhibit different spatial patterns in the ICP. Even for a single element, the ionic and atomic emission transitions exhibit different spatial patterns. Usually a single compromise viewing position is chosen for most determinations of concentration. The commercial availability of fast sequential monochromators has made sequential-element determinations an important analytical tool. In contrast to simultaneous multielement measurements, the fast sequential measurements offer the theoretical possibility of optimization of all parameters affecting emission. With proper computer control, parameters such as power level, argon flow rate, sample introduction rate, and observation region in the plasma can be optimized and the settings reproduced for each element prior to measurement. Several authors have utilized multivariate (simplex) techniques in optimization studies. This paper focuses on a single aspect of optimization, observation position, presents a simple method for obtaining emission profile data, and compares results of compromise viewing position vs. individual element optimized viewing position on signal-to-background ratios.
Thomas R. Fogg, "Simple ICP Spatial Profiles: Optimization of Observation Position," Appl. Spectrosc. 42, 170-172 (1988)