Development of an ICP-IDMS method for accurate routine analyses of toxic heavy metals in polyolefins and comparison with results by TI-IDMS

An inductively coupled plasma isotope dilution mass spectrometric (ICP-IDMS ) method was developed as a suitable method - with respect to its sensitivi ty, precision, accuracy, and time-consumption - for the analysis of toxic h eavy metal traces (Pb, Cd, Cr, and Hg) in polyolefins. Results for Pb, Cd, and Cr were compared with those obtained by thermal ionization isotope dilu tion mass spectrometry (TI-IDMS), which was used as a reference method. Bec ause of its high first ionization potential and its high volatility mercury could not be determined by TI-IDMS. A multi-element spike solution, contai ning isotopically enriched (206)pb, Cd-116, Cr-53, and Hg-201, was used for the Isotope dilution step. Decomposition of the polyolefin samples was car ried out with concentrated HNO3 at temperatures of about 300 degrees C in a high pressure asher (HPA). This procedure decomposes polyolefins completel y and allows isotopic equilibration between sample and spike isotopes. Dete ction 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 differe nt commercially available polyethylene samples heavy metal concentrations i n the range of < 5 ng/g to 4 x 10(3) ng/g were analyzed. Both mass spectrom etric methods were applied within the EU project ''Polymeric Elemental Refe rence Material (PERM)" for the certification of two polyethylene reference materials. The ICP-IDMS results agreed very well with those of TI-IDMS whic h demonstrates the accuracy of the ICP-IDMS method also suitable for routin e analyses.