Developmeent of an ICP-IDMS method for accurate routine analyses of toxic heavy metalsin polyolefins and comparison with results by TI-IDMS

摘要

An inductively coupled plasma isotope dilution mass spectrometric (ICP-IDMS) method was developed as a suitable method -with respect to its sensitivity, pre- cision, accuracy, and time-consumption -for the analysis of toxic heavy metal traces (Pb, Cd, Cr, and Hg) in poly- olefins. Results for Pb, Cd, and Cr were compared with those obtained by thermal ionization isotope dilution mass spectrometry (TI-IDMS), which was used as a reference method. Because of its high first ionization potential and its high volatility mercury could not be determined by TI- IDMS. A multi-element spike solution, containing iso- topically enriched 206Pb, 116Cd, 53Cr, and 201Hg, was used for the isotope dilution step. Decomposition of the poly- olefin samples was carried out with concentrated HNO3 at temperatures of about 300°C in a high pressure asher (HPA). This procedure decomposes polyolefins com- pletely and allows isotopic equilibration between sample and spike isotopes. Detection limits of 16 ng/g, 5 ng/g, 164 ng/g, and 9 ng/g were obtained for Pb, Cd, Cr, and Hg by ICP-IDMS using only sample weights of 0.25 g. In different commercially available polyethylene samples heavy metal concentrations in the range of< 5 ng/g to 4 x 103 ng/g were analyzed. Both mass spectrometric methods were applied within the EU project "Polymeric Elemental Reference Material (PERM)" for the certification of two polyethylene reference materials. The ICP-IDMS results agreed very well with those of TI-IDMS which demon- strates the accuracy of the ICP-IDMS method also suit- able for routine analyses.