On-line dilution, steady-state concentrations by tandem injection and merging stream. Application to inductively coupled plasma atomic emission spectrometry sequential multi-element soil analysis

Abstract

Recently developed flow injection on-line dilution methods, i.e., the merging stream and tandem injection, which yield steady-state concentrations, have been applied to the analysis of reference soil sample digests by inductively coupled plasma atomic emission spectrometry. Direct or on-line dilution determinations were applied, with dilutions ranging from 1.8 to 15 for both dilution methods. Higher dilutions are not feasible, especially when trace elements are involved. A variable speed peristaltic pump was used to limit the total flow-rate by the merging-stream dilution method to 2 ml min^–1. This permitted the design of a flow module with one set of coils and a flow configuration suitable for all dilutions. Varying the dilution required only the variation of the peristaltic pump flow tube diameters. Selecting the required dilution for the tandem injection method was carried out with no manual operations and involved only pre-programming of the injection time and the injection cycle period. The results obtained exhibit comparable accuracy and precision for major and minor elements to those obtained by direct determination. By varying the dilution for the determination of trace elements, screening the optimum dilution(s) suitable for the determination of each trace element is possible.