An Improved Chemical Extraction Procedure for the Sr Isotope Analysis of Liquid Agrifood Samples Applied to...

We describe a new simplified sample preparation technique, based on dual chromatography for the analysis of ⁸⁷Sr/⁸⁶Sr in liquid agri-food samples. We applied this approach for authenticating the origin of maple syrup products in Quebec, characterizing the ⁸⁷Sr/⁸⁶Sr of soil profiles from geologically distinct maple groves, including maple tree components and maple syrup products.

In our simplified technique, 3 mL of the organic liquids was poured into a 15-mL centrifuge tube, diluted with 10 mL of Mill-Q H₂O, and manually shaken to produce a thin juice. The thin juice was subsequently loaded in two 7.5 mL aliquots onto 10-mL Bio-RadTM chromatography columns containing 4 mL of cleaned AG50-X8 resin (100-200 mesh in a 1-N HCl solution). Once the sample was absorbed by the resin, the organic fraction of the thin juice was eluted by adding 3 × 5 mL of 1-N HCl. The Sr and other cations were subsequently recovered by adding 2 × 5 mL of 6-N HCl.

The maple groves and the ⁸⁷Sr/⁸⁶Sr ratios for maple syrup from 39 different producing areas in Quebec indicated that no isotope fractionation occurs between the syrup, the maple trees, and the corresponding labile fraction of the soil they grew upon. This suggests that ⁸⁷Sr/⁸⁶Sr provides a reliable isotope fingerprint for the provenance of maple syrups. Gathering available agri-food ⁸⁷Sr/⁸⁶Sr data across the Quebec province, we constructed the first bioavailable ⁸⁷Sr/⁸⁶Sr map based on actual agri-food data.

This study reported an improved method for Sr separation for ⁸⁷Sr/⁸⁶Sr studies in liquids by combining two different cation-exchange chromatography steps. Data were used to develop a bioavailable ⁸⁷Sr/⁸⁶Sr map that can be used to predict the geographical origin of agrifood products from southern Quebec.