Total uncertainty budget as method evaluation criterion for the determination of tracer (Cd-111) cadmium and indigenous cadmium in soil column effluents with ICP-MS

For the evaluation of different analytical methods the best achievable fina l uncertainty can be used as the criterion. Evaluation of an analytical met hod on this basis includes the magnitude and also the robustness of the unc ertainty budget. This evaluation was applied to laboratory-scale migration experiments on soil columns. These experiments were performed in order to e stimate soil transport parameters of heavy metal pollutants (cadmium). In t hese studies a tracer (stable Cd-111 isotope), having nearly the same physi co-chemical properties as the pollutant of concern, was added on top of a c ontaminated soil and the column effluents were fractionally collected at th e bottom. This paper presents three different calculation models, derived f rom the isotope dilution equation, for the simultaneous determination of th e concentration tracer cadmium, [Cd-t], and indigenous cadmium, [Cd-n], in soil column effluents with ICP-MS. The methods differ in the method of calc ulation but are, in principal, based on the same measurements. The uncertai nty budgets of the different methods were used in the evaluation. In additi on to the magnitude of the total uncertainty, the boundary conditions of so me parameters were investigated in detail. The influence of the following p arameters on the uncertainty budget was studied: the concentration level of cadmium, the isobaric interference of tin and the molar fraction of indige nous cadmium.