Producing SI-traceable reference values for Cd, Cr and Pb amount contents in polyethylene samples from the Polymer Elemental Reference Material (PERM) project using isotope dilution mass spectrometry

The present paper describes the certification of the amount content of Cd, Cr and Pb in two different polyethylene materials within the third phase of the Polyethylene Elemental Reference Material (PERM) project. The analytic al procedure to establish the reference values for Cd, Cr and Pb amount con tents in these materials is based on isotope dilution mass spectrometry use d as a primary method of measurement. Cd and Pb were measured with inductiv ely coupled plasma-mass spectrometry and Cr with positive thermal ionizatio n-mass spectrometry. The decomposition of the polymer matrix was carried ou t using a high pressure asher, Reference values for amount content, traceab le to the SI-system, have been obtained for these three elements in both of the polyethylene samples of PERM. For each of the certified amount content values an uncertainty budget was calculated using the method of propagatio n of uncertainties according to ISO and EURACHEM guidelines. The measuremen t procedures, as well as the uncertainty calculations, are described for al l three elements. In order to keep the whole certification process as trans parent as possible, the preparations of various reagents and materials as w ell as the sample treatment and blending are described in detail. The mass spectrometry measurements and the data treatment are also explained careful ly. The various sources of uncertainty present in the procedure are display ed in the uncertainty budgets. The obtained combined uncertainties for the amount content values were less than 2% relative (k=1) for all investigated elements. The amount contents were in the mu mol/kg range, corresponding t o mg/kg levels.