Development of pretreatment protocols for Sr isotope ratio measurements in rice flour: near-quantitative recovery of Sr due to H₃BO₃ treatment after HF digestion

Abstract

The radiogenic isotope ratio of strontium (⁸⁷Sr/⁸⁶Sr) is a possible tool for food authentication. In addition, Sr stable isotope ratios (⁸⁸Sr/⁸⁶Sr) have been focused on as an important tracer for understanding the global carbon cycle. Rice is the staple food for Japanese people and is a sample for which there is a high need for Sr isotope ratio measurements. However, a decrease in Sr recovery was observed in the Sr separation process prior to Sr isotope ratio measurement of rice samples, resulting in a concern that the isotopic fractionation that occurs during the separation process could compromise the accuracy of the measurements. As a possible cause of this, it was suggested that the hydrofluoric acid added to dissolve silicate during the acid digestion of rice samples formed a calcium fluoride colloid, and that Sr was coprecipitated and trapped in the colloid. In this study, we attempted to dissolve CaF₂ and recover Sr trapped in the colloid by boric acid treatment, and were able to improve the recovery rate to about 98 %.