Strategies for resin reuse in Sr/matrix separation prior to isotope analysis

• This study tested regenerated resin for Sr/matrix separation pre isotope analysis; • Tests were conducted using both reference material and real sample batches; • Different protocols were applied for the resin washing steps; • Resin reuse preserved Sr isotope ratios in isotopically uniform batches; • For unique or heterogeneous samples, resin reuse is not recommended. One of the key passages to achieve an accurate and precise Sr isotope ratio ( 87 Sr/ 86 Sr) measurement is the Sr/matrix separation. Traditionally this step is accomplished using a Sr-spec resin which allows the Sr recovery eliminating the main interferent species (namely Ca, Rb, Pb). While this application is consolidated, few details are available in literature regarding the possibility to reuse the resin for the consecutive separation of Sr from multiple samples. To deepen this aspect, in this study different tests were conducted both using certified and in-house reference materials, to check the performance of the separation in different working conditions and testing solutions of HNO 3 and HCl for the resin washing between consecutive use cycles. These tests confirmed that resin reuse guarantees average Sr recovery higher than 95%, with a negligible presence of interfering species in the final solution, and no effect on the Sr isotope ratios. However, since in no case a quantitative Sr recovery was achieved, the presence of Sr residues on the resin might limit this application if different samples are treated on the same resin. Tests with batches of real samples showed that using a mild washing with HNO 3 (0.05 M), although residual cross-contamination was present, no significant alteration of the sample 87 Sr/ 86 Sr ratios occurred, in case of homogeneous ratios. At increasing levels of heterogeneity, even the use of HCl in the resin washing might be not sufficient. This study demonstrated the feasibility of resin reuse, reducing its consumption, associated costs, and lab workload, without affecting the accuracy of the results when working with sample replicates or when a low-to-medium difference in the 87 Sr/ 86 Sr ratio of consecutive samples is expected.