Development of a Chelex-100 based three-step chromatographic procedure for nickel isotope analysis in geological samples

Nickel isotopes have been employed to trace various processes such as the weathering of mafic and ultramafic rocks, mineral adsorption and co-precipitation, and the metabolism of methanogenic archaea. Nickel isotopes have displayed significant potential for application, regardless of whether the processes occur at high or low temperatures. However, the currently employed nickel isotope separation methods have certain limitations in terms of separation effectiveness, blank contribution, separation efficiency, and cost-effectiveness of the resin used. Therefore, in this study, we have devised a user-friendly three-step chromatographic procedure that relies on the Chelex-100 resin and other resins for the efficient isolation and purification of nickel from a wide array of geological samples. The three resins utilized in this procedure are Chelex-100, AGMP-1M, and AGMP-50. It is worth noting that Chelex-100 has exhibited exceptional performance in eliminating alkali metals, alkaline earth metals, and iron. Following chromatographic separation, the recovery of nickel surpassed 96%, with a procedural blank below 1.2 ng. To evaluate the procedure's effectiveness, we conducted nickel isotope measurements on nine geological reference materials (BCR-2, GSR-3, GSP-2, NOD-A-1, GSMC-1, SGR-1, SDO-1, GSD-5a, and GSD-23) using MC-ICP-MS. The obtained values were consistent with previously published data, confirming the reliability of our results. The findings of our study establish the applicability of the developed separation procedure for nickel isotope analysis in various geological samples. User-friendly chromatographic procedures using Chelex-100 achieve high recovery and minimize procedural blanks in nickel isotope analysis.