Analytical factors to be considered for the application of enriched strontium spikes to monitor biological systems

Abstract

A full metrological protocol for data processing during isotope pattern deconvolution of an enriched Sr isotope double spike as an intrinsic marker in a biological system is described for the first time. The study is based on data gained during a transgenerational marking study, where the transfer of a Sr isotope double spike (⁸⁴Sr and ⁸⁶Sr) from female spawners of the common carp (Cyprinus carpio L.) to the centre of the otoliths of their offspring was studied by (LA)-MC-ICPMS. Special emphasis is made on evaluating different data processing strategies, whereat the following analytical key parameters are considered: the blank (Kr, Sr and Rb), variation of the natural Sr isotopic composition in the sample, mass bias, interferences (Rb) and total combined uncertainty. Compared to other systems, which have been used for spiking and subsequent deconvolution (e.g. Ba), isotope pattern deconvolution (IPD) of Sr (double) spikes using multiple linear regression analysis is limited by the number of degrees of freedom available (as a result of the number of natural isotopes). Therefore single parameters have to be evaluated comprehensively in order to develop a proper strategy for isotope pattern deconvolution along with uncertainty calculations. The developed correction strategies allow for isotope pattern deconvolution of a Sr double spike to sample batches marked at low spike amounts using enriched ⁸⁶Sr/⁸⁴Sr double spikes of relative differences of the ⁸⁶Sr/⁸⁴Sr ratio of >15%, with respect to the total combined uncertainties entailed. Furthermore, Sr isotope double spikes were successfully calculated in samples with natural Rb/Sr molar fraction ratios of up to ½, which bears great potential for applications of enriched Sr isotope tracers in biological systems that are being studied using LA-MC-ICPMS. Finally, recommendations for data evaluation of the enriched Sr isotope tracers in biological samples are given.