ICP-MS – determination of chemical elements in different types of cork stoppers

Cork is the bark of Quercus suber tree. This bark has an amazing number of possible uses, particularly for the production of cork stoppers. Metals in cork can come from different sources; it could be from the field or the different industrial process that the cork suffers before the transformation to the final product [1]. There are different types of corks such as natural cork that is a 100% natural product, agglomerated stoppers which can be manufactured by individual moulding or extrusion, and in both methods, the agglutinated substance used to connect the cork granules is approved for the use in food contact materials. These stoppers are entirely made from granulated cork from sub-products from the production of natural cork. In the present work, cork samples from different steps of the industry process were analysed. The following chemical elements were determined by Inductively Coupled Plasma Mass Spectrometry (ICP-MS): Vanadium (V), Chromium (Cr), Nickel (Ni), Arsenic (As), Cadmium (Cd), Selenium (Se), Lead (Pb), Cobalt (Co), Zinc (Zn), Copper (Cu), Manganese (Mn) and Strontium (Sr). The method for sample preparation of cork stoppers consisted on grinding and homogenizing samples, followed by an acid-assisted microwave digestion to destroy the organic matrix. For quality control purposes parameters such as repeatability, linearity of the calibration curve, blanks or recovery of spiked samples were monitored and complied with the acceptance criteria established by the laboratory. Several elements were present in the samples in amounts above the quantification limits (ppb or ppt level). However, and according to European legislation [2], the total amount of the elements found was always below the maximum limit. We may conclude that there’s no contamination of the chemical elements during the manufacturing process of agglomerated cork stoppers.