Improvement of Determination of Trace Amounts of Arsenic and Selenium in Slim Coffee Products by HG-ICP-OES

Abstract

A method for the determination of total inorganic arsenic and selenium in slim instant coffees using hydride generation inductively coupled plasma optical emission spectrometry (HG-ICP-OES) was proposed. Various sample preparation procedures, including the traditional total decomposition by the hot-plate or microwave heating in a HNO3/H2O2 mixture and alternative procedures based on the solubilisation in aqua regia or tetramethyl ammonium hydroxide (TMAH) and the dilution only with water or a low concentrated HNO3 solution were examined and compared. Corresponding As and Se hydrides were generated in the reaction of an acidified sample solution with the NaBH4 reductant in the presence of antifoam A. A small sample preparation with aqua regia in an ultrasonic bath followed by the pre-reduction with KI–ascorbic acid in the HCl medium for total As and the boiling with HCl for total Se were found to be optimal. The external calibration using standards treated and measured as the same as samples were applied for the analysis. Limits of detection (LODs) of 0.96 and 0.55 ng ml−1 were assessed for As and Se, respectively. The precision (as the relative standard deviation [RSD]) was within 1.6–7.1 %. The accuracy of the method was confirmed by the recovery test and the analysis of a standard reference material (non-fat milk powder, SRM 1459). The developed procedure was applied for the analysis of six commercial instant slim coffee products available in the Polish market and it was found that these products contain traces of As (0.114–0.247 μg g−1) and Se (0.089–0.137 μg g−1).