ONLINE ISOTOPE-DILUTION ANALYSIS WITH ICPMS USING REVERSE FLOW-INJECTION

A simple now injection manifold is described to perform the addition o f isotopic spikes to aqueous samples online with ICPMS, The analysis i nvolves one multielement spike injection in the sample carrier and ano ther injection of the spike solution in a standard carrier. This stand ard must contain one element which is not present in the spike solutio n, to allow the determination of the dispersion coefficient. The same standard also allows a reverse isotope dilution (ID) analysis, in addi tion to corrections for mass discrimination and any spectroscopic inte rference on one of the two isotopes used for the ID analysis, This now injection approach, therefore, requires only one isotope free of spec troscopic interference for elements whose isotopic distribution does n ot vary in nature (two isotopes are still needed for other elements si nce the ''natural'' ratio must then also be determined). No preliminar y analysis of the sample is required prior to the actual ID analysis. Furthermore, the concentration profile resulting from the flow injecti on allows the selection of the best isotopic ratio in terms of error p ropagation. This approach, therefore, makes ID analysis as simple as a n external calibration but with added accuracy and precision. It was s uccessfully applied to the analysis of a river water certified referen ce material and to saline water.