Current interest in analytical chemistry concerns the traceability of analytical measurements to the International System of Units (SI) and estimation of their uncertainties. Primary methods of measurement achieve traceability directly without intermediate reference standards or materials and without significant empirical correction factors. In this work, isotope dilution mass spectrometry was regarded as such a primary method and wastewater as a matrix of significant ecological and toxicological relevance. In that sense, a validation study was performed for total (dissolved + particulate) element determination (Cd, Cr, Fe, Ni, Pb and Zn) in acidified (pH < 2) wastewater samples by using on-line isotope dilution mass spectrometry with inductively coupled plasma (OID-ICP-MS) after acid extraction in a microwave system.Emphasis was placed on the OID-ICP-MS method and its validation by comparison against direct external calibration mass spectrometry with inductively coupled plasma analysis (ICP-MS), including differences in calibration strategies. Good agreement (trueness) between the two analysis methods was achieved for all trace metals involved. However, OID-ICP-MS offers more accurate and precise results with smaller measurement uncertainties, when properly applied, compared to external calibration. Thus, OID-ICP-MS proved to be an ideal solution for routine wastewater analysis, increasing the sample throughput without any previous sample handling and improving the quality and reliability of the analytical results.
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