Determination of Trace Elements in Polished Asian Rice Using XRF spectrometer Equipped with Polarization Optics and Its Application to Identification of Their Production Area

Abstract

The trace elemental analysis of polished rice was performed using X-ray fluorescence (XRF) analysis in order to characterize the geographical origins. Short, medium or long grains of samples collected from 5 origins (Japan, China, Malaysia, Bangladesh, and Myanmar) were powdered and prepared as pressure-molded tablets for analysis. The long-grain types with dry texture required a higher pressure (12 tonf/cm²) and a longer time (10 minutes) for molding. By using an energy-dispersive XRF spectrometer equipped with three-dimensional polarization optics and employing three secondary targets (Ti, Ge, and Zr), 10 elements (P, S, Cl, K, Ca, Mn, Fe, Cu, Zn, Rb) were detected in 15 minutes. The concentrations of P, Mn, Fe, Cu, Zn and Rb were quantified by using calibration curves of each element. Using the elemental concentrations and the stable isotope ratios (δ¹³C, δ¹⁵N, δ¹⁸O), the polished-rice samples were examined by principal-component analysis to classify the geographical origins. The geographical discrimination progressed by combining the elemental compositions and the isotope ratios and, consequently, the Asian rice samples were characterized according to the graphical origins by the complemental parameters.