Multi-element optimization of the operating parameters for inductively coupled plasma atomic emission spectrometry with a charge-transfer device detection system: a study of the effects of different response functions

Abstract

A new response function for ICP-AES is proposed in which the resultant compromise plasma conditions are independent of the concentration of the analytes in the test solution. The response function is designed to be used in situations where the concentrations of the analytes in the sample are unknown, or, when many samples, of varying composition, are to be analysed. In addition, the use of the signal-to-root background ratio (SRBR) as the measurement of the analytical performance of an element for multi-element analysis by ICP-AES, with a charge-coupled device detector, is described. The use of the SRBR was found to give better detection limits than those obtained with the more commonly used signal-to-background ratio (SBR). For instance, the detection limit for Mn II at 257.610 nm is improved from 13 ng ml^–1 when using the SBR and the proposed response function, to 2.8 ng ml^–1 when using the SRBR. The compromise operating parameters, and hence detection limits for the analytes, were shown to be independent of the composition of the test solution for the new function. In comparison, the detection limit of Mn II varied between 2.9 and 40 ng ml^–1, depending on the test solution composition when optimizing with a previously reported response function. Furthermore, biasing the proposed function for a particular analyte by increasing a weighting parameter is demonstrated. For instance, the detection limit of Pb I at 280.199 nm improved from 54 to 41 ng ml^–1, by increasing the weighting parameter for Pb from 1 to 10.