Determination of cadmium in rice by electrothermal atomic absorption spectrometry using aluminum as permanent modifier

Abstract

In this paper, the use of aluminum as a permanent modifier for the determination of cadmium in rice by electrothermal atomic absorption spectrometry (ETAAS) was investigated. The optimized experimental conditions, which employed a full two-level factorial design, pyrolysis and atomization curves, were as follows: aluminum mass of 400 μg, pyrolysis temperature of 400 °C, pyrolysis time of 20 s and 1,800 °C for atomization temperature. Under these conditions, cadmium concentrations could be determined in rice with limits of detection and quantification of 2 and 6 ng g⁻¹, respectively, as well as a characteristic mass of 1.3 pg. The precision, expressed as relative standard deviation (RSD%), was 1.67% for a rice sample with a cadmium concentration of 41.3 ng g⁻¹. The accuracy was confirmed by analysis of a certified reference material of rice flour that was provided by the National Institute for Environmental Studies, Japan. Experiments involving the analyte addition technique demonstrating that the external calibration technique using aqueous standards could be used for quantification of cadmium in rice. The proposed method was used to determine the cadmium content of thirty-four rice samples acquired in supermarkets from Bahia State, Brazil. The rice samples were digested using nitric acid and hydrogen peroxide in a closed system, using a digester block and cold finger. The cadmium concentrations varied from 11.6 to 44.9 ng g⁻¹, with an average content of 30.1 ng g⁻¹. A preliminary study demonstrated that the cadmium contamination in rice decreased after cooking using a microwave oven.