Comparison of different numerical approaches for multiple spiking species-specific isotope dilution analysis exemplified by the determination of butyltin species in sediments

An examination and comparison of all the mathematical approaches for multiple spiking species-specific isotope dilution analysis published so far in the literature is presented in this work with the determination of TBT and DBT in sediments. The basis of four different numerical approaches -Calculation of Stable Isotope Concentrations, Speciated Isotope Dilution Analysis, Species-Specific Isotope Dilution Analysis and Isotope Pattern Deconvolution -are explained and compared in terms of complexity, analytical figures of merit and specific advantages. The four methodologies have been found to provide exactly the same degradation-corrected concentrations for DBT and TBT in all samples even when different degradation extents are taking place. However, slight differences in the degradation factors have been obtained between two pairs of methods, being in all cases lower than the corresponding instrumental uncertainty of the values. The capability of extending the methodologies to a higher number of analytes by the use of additional enriched species as well as the specific advantages of the different methods is discussed. In this sense, it has been demonstrated that Calculation of Stable Isotope Concentrations and Isotope Pattern Deconvolution provide additional advantages such as the qualitative information on any non-spiked species present in the samples. In addition, using Isotope Pattern Deconvolution the performance of a new internal procedure for mass bias correction without the additional measurement of reference isotope ratios is presented.