Preparation of cadmium‐containing brown rice grains as calibration standards for X‐ray fluorescence analysis of cadmium in rice grains

A preparation method for Cd‐containing brown rice grains as calibration standards was developed for X‐ray fluorescence (XRF) analysis of Cd in rice grains. Calibration standards were prepared by adding 10 g of base rice grains (from Japan) to 100 ml of methanol containing 5?100 µg of Cd. The mixture was heated, cooled, and stored in a silica gel desiccator. Seven grams of each calibration standard was packed into a polyethylene cup (32‐mm internal diameter and 23‐mm height) covered with a 6‐µm‐thick polypropylene film and then subjected to XRF analysis. The calibration curves of Cd in brown and white rice grains showed good linearity in 0.50?10 mg kg^?1. The detection limits of Cd in brown and white rice grains were 0.14 and 0.12 mg kg^?1, respectively. The slopes of the calibration curves for Cd in brown and white rice grains were slightly different owing to absorption effects. The absorption effects were corrected using the ratio of the intensity of Cd Kα to that of Rh Kα‐Compton scattering. After correction, the calibration curves of Cd in brown and white rice grains showed identical slopes. The spike test for 5 mg kg^?1 of Cd in white rice grains (from Thailand), using the corrected calibration curves, showed quantitative recoveries (92?97%). Copyright © 2013 John Wiley & Sons, Ltd.