Imaging of Elements Distribution in Rice by Laser Ablation Inductively Coupled Plasma Mass Spectrometry

Rice is a food consumed worldwide and there is a grown concern about its nutritional value, as well as the concentration of contaminant elements. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was employed in the present work for determination and imaging of Mg, Mn, Cu, Co, Fe, Zn, As, Sr, Sb, Ba and Pb in grains of white, parboiled, and whole (brown) rice. The elements quantification was achieved by using external calibration whereas filter paper discs served as support for the reference solutions and matrix matching. Accuracy was ensured by analysing two certified reference materials (CRMs) pressed into pellets. Investigations were carried out to evaluate the distribution of the elements on the surface and external layers of the grains. For that purpose, the surface of rice grains fixed on a glass support was ablated line-by-line and the ablation repeated three times. The images generated from laser ablation revealed that the investigated elements were not homogeneously distributed in the analysed parts of the grains. Except for Pb, the investigated elements were detected in three layers of the rice grains, but it was observed that the elements concentrations decreased from the surface to more internal layers. Lead was detected only in the first layer of white and whole rice and in the first and second layers of parboiled rice.