Metrological traceability chain for PCBs: I.N.Ri.M. activity

Metrology in chemistry has its own features which distinguish it from classical metrology. In particular, the application of metrological concepts to the determination of organic pollutants in different matrices is a challenge. In fact, it deals with an enormous amount of different compounds, which are present at various concentrations, often at trace level, and can interact with the matrix constituents. For such kinds of measurements, the achievement of metrological traceability is a non trivial aspect and one of the tasks to be carried out is the evaluation of measurement uncertainty taking into consideration all relevant contributions. At I.N.Ri.M. a research activity dealing with organic analysis has started. The first analytes taken into account are polychlorinated biphenyls (PCBs). The choice is due to their relevance as environmental pollutants, a reason that led to their inclusion among the twelve classes of Persistent Organic Pollutants (POPs), selected by United Nations Environment Programme (UNEP) under the Stockholm Convention on POPs in 1997. Traceable PCBs standards of different congeners in iso-octane are prepared by accurate weighing by diluting certified reference materials. A correct uncertainty budget is developed taking into account all the possible uncertainty sources, deriving both from the reference materials and from the weighing process. The PCBs are determined by a gas-chromatograph coupled with a single quadrupole mass spectrometer (GC-MS). The interpretation of mass spectra obtained in scan mode allows the identification of the different congeners. GC-MS is calibrated using the traceable standard solutions prepared by weighing. The PCBs congeners amount in unknown samples is determined by comparing the ion current generated by each congener with respect to the calibration curve, assuring metrological traceability of results. At present, the aim is to verify the achievement of metrological traceability for PCBs determination on real matrices, and a method including all the preparation steps necessary in practical applications is under developmen