Determination of strontium isotope ratio of brown rice for estimating its provenance

Abstract

The strontium isotope ratio (⁸⁷Sr / ⁸⁶Sr) of brown rice (Oryza sativa L.) was determined by multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS) in order to evaluate the values of ⁸⁷Sr / ⁸⁶Sr for use in the estimation of the area of rice production. Sample solutions were prepared from 5 g of rice samples using the acid (HNO₃-HClO₄-HF) digestion method. Removal of rubidium from the sample solutions was performed using ion-exchange resin (Dowex 50W X8). The Sr isotope ratios were determined with a precision of < 0.01% (RSD, repetitions = 60) by MC-ICP-MS. Typical analysis time for a single sample was about 15 min, reflecting the high sample throughput. The Sr isotope ratios of the Japanese rice samples ranged from 0.706 to 0.709. The Sr isotope ratios of the Chinese and Vietnamese rice samples (0.710 to 0.711) were slightly higher than those of almost all the Japanese samples. Australian rice showed the highest Sr isotope ratio (0.715 to 0.717) among all the rice samples examined. In contrast, the Sr isotope ratio of Californian rice (0.706) was lower than that of almost all the Japanese samples. The variation in the ⁸⁷Sr / ⁸⁶Sr ratios for the rice samples analyzed in this study clearly demonstrated that the Sr isotope ratios could provide a key information for the estimation of rice provenance.

Key Words:

• brown rice
• geographic origin
• ion-exchange method
• multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS)
• strontium isotope ratio