Uncertainty calculations for amount of chemical substance measurements performed by means of isotope dilution mass spectrometry as part of the PERM project Original Research Article

DSM Research was a partner in the certification round of a project, organized under the auspices of the European Commission’s Fourth Framework Standards Measurement and Testing Programme, to produce two polyethylene reference materials. The project, entitled Polymer Elemental Reference Material (PERM SMT4-CT95 3024) required the determination of the concentrations of Cr, Cd, Hg and Pb in two polyethylene materials which were identified as PERM T3 high and PERM T3 low. Analysis was accomplished by means of an in-house developed ‘on-line’ isotope dilution mass spectrometry (IDMS) method using quadrupole ICPMS. This paper focuses on calculating the uncertainty of these IDMS measurements. Since all analytical measurement results have an uncertainty associated with them, it is considered best practice, within metrological circles, to state an uncertainty, as an integral part of any measurement result. We used a Monte Carlo simulation to estimate the uncertainties associated with the measured concentrations of Cr, Cd, Hg and Pb in the PERM T3 (high and low) materials. By participating in an interlaboratory exercise we have been able to compare our results with those of other laboratories that used both classical IDMS and other techniques. Our results agreed with the overall mean of all participating laboratories, within stated uncertainties. Furthermore our uncertainties derived from Monte Carlo simulation were of the same magnitude as those obtained for the classical IDMS approach.