Determination of PCBs in organic solutions: an example of traceability chain

Polychlorinated biphenyls (PCBs) are extremely persistent and widespread environmental pollutants. Because of their potential health impacts on a wide variety of biota, including human beings, they belong to the twelve classes of Persistent Organic Pollutants (POPs) selected by United Nations Environment Programme (UNEP) under the Stockholm Convention on POPs in 1997. For this reason, the European Community requires the development of measurement methods and standards in order to obtain comparable, consistent, reliable and high quality results for the measurements of these kinds of compounds. The present work deals with the establishment of a traceability chain for the analysis of various PCBs congeners in organic solutions. Traceability is the property of the result of a measurement or the value of a standard whereby it can be related to stated references, usually national or international standards, through an unbroken chain of comparison all having stated uncertainties. The unbroken chain of comparisons is called traceability chain. A correct traceability chain needs to be established in order to obtain high quality reliable results and to compare results of measurements carried out in different places and by different laboratories. Traceable PCBs standards in iso-octane were prepared by accurate weighings from certified reference materials; an uncertainty budget was made, which took into account all the possible uncertainty sources, as the uncertainty of the reference materials and the uncertainty in the mass measurements. Various PCBs congeners were determined via gas-chromatography coupled with mass-spectrometry. The identification of the PCBs congeners in different organic solutions was made by means of the interpretation of the mass spectra obtained in the scan mode. The gas chromatograph coupled with an ion trap mass spectrometer was calibrated using the traceable standards prepared by weighing. The PCBs congeners amount was determined comparing the ion current of proper mass chromatograms of specific fragment ions, selected on the basis of the mass spectra of each congener