DETERMINATION OF TRACE-ELEMENTS IN FOOD CONTACT POLYMERS BY SEMIQUANTITATIVE INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY - PERFORMANCE EVALUATION USING ALTERNATIVE MULTIELEMENT TECHNIQUES AND IN-HOUSE POLYMERREFERENCE MATERIALS

The determination of trace elements in a wide range of polymers intend ed for food contact use was carried out by inductively coupled plasma mass spectrometry (ICP-MS). Microwave digestion in concentrated nitric and sulfuric acids enabled rapid wet oxidation of all the polymers, t o give samples suitable for introduction into the plasma. Semiquantita tive multi-element screening of the polymer digests could then be carr ied out using a single indium internal standard. Limits of detection f or the polymers were generally in the order of 1 mg kg(-1). Owing to t he paucity of suitable standard reference polymer materials required f or validation of the procedures used, a series of in-house reference m aterials was prepared by incorporating a cocktail of metal stearates i nto a range of polymer materials via the melt. Levels of elements in t hese reference materials were established by two reference methods: di rect neutron activation analysis (NAA) and a quantitative ICP-MS metho d. Results fog the two reference methods were encouragingly close to n ominal added values and replicate analyses indicated that homogeneity was good. Further analysis of the materials using laser ablation ICP-M S confirmed that the distribution of elements within the polymer matri x was satisfactory. In addition, NAA was carried out On the great majo rity of the polymer samples as a further aid to validation of the semi -quantitative multi-element ICP-MS method.