Direct determination of cadmium in rice by solid sampling electrothermal vaporization atmospheric pressure glow discharge atomic emission spectrometry using a tungsten coil trap

Abstract

In this paper, a fast, cost-effective and sensitive method for the direct determination of Cd in rice was developed based on miniaturized direct current atmospheric pressure glow discharge microplasma (4 mm × 10 mm) atomic emission spectrometry (APGD-AES) coupled with solid sampling electrothermal vaporization with a tungsten coil trap (ETV-TC). During the analysis, milligram (1–15 mg) rice samples firstly went through dehydration and pyrolysis with Cd being vaporized from the residue and trapped on a cold tungsten coil. Then the trapped Cd was released from the tungsten coil by heating and introduced into an APGD plasma for excitation via an Ar/H₂ stream. The whole process takes approximately 3 min. The operating parameters of the ETV-TC device and APGD were optimized and possible interference from coexisting ions and organic substances was also evaluated. Under the optimized conditions, the detection limit for Cd (228.8 nm) was calculated to be 2.6 pg, namely 0.26 μg kg⁻¹ using 10 mg of rice sample. The accuracy of the proposed method was validated by the analysis of a rice certified reference material (GBW(E)100360). In addition, it was also successfully applied to the analysis of 7 rice samples and compared with conventional microwave digestion ICP-MS methods. Very good agreement was obtained between the measured and certified values of Cd in the CRMs or values obtained using well-established ICP-MS methods, demonstrating its reliability for the determination of traces of Cd in rice. The proposed method provides a promising, simple and low-cost approach to develop a portable instrument for routine monitoring of Cd contamination in rice samples.