Fast method of elements determination in slim coffees by ICP OES

Six sample preparation procedures, i.e., the total decomposition in a HNO3 and H2O2 mixture by microwave-assisted or hot-plate heating, a partial decomposition by means of solubilisation in aqua regia or tetramethyl ammonium hydroxide and simple dissolution in diluted HNO3 or in H2O, for the determination of the total content of Ba, Ca, Cd, Cr, Cu, Fe, Mg, Mn, Ni, P, Pb, Sr and Zn in slim instant coffees using inductively coupled plasma optical emission spectrometry were compared. The performance of procedures was determined based on the precision and the accuracy of results and limits of detection of elements. It was found that the extraction with aqua regia provides the best results, i.e., limits of detection of elements within 0.11-108 ng mL−1, the precision of 0.6-5% and the accuracy better than 5%. Elements' concentrations agree with those after the wet digestion in the HNO3 and H2O2 mixture, therefore this procedure is a simple and fast alternative to complete sample decomposition procedures and can be easily applied for routine analyses. Six commercial slim coffee products were analysed with the proposed procedure.