A calculation mode for the correct GC/ECNI-MS-SIM determination of polychlorinated terphenyls in the presence of high excesses of polychlorinated biphenyls

Polychlorinated terphenyls (PCTs) are a class of persistent organic pollutants difficult to analyze by gas chromatography with mass spectrometry operated in the selected ion monitoring mode (GC/MS-SIM) in environmental samples due to the retention time and mass range overlap with polychlorinated biphenyls (PCBs). To overcome these drawbacks, we developed and evaluated a mathematical calculation algorithm which allows to detail the interference of PCT congeners in GC/electron capture negative ion (ECNI)-MS-SIM chromatograms by PCBs. The calculation takes advantage of the abundance and ratio of two suitable isotope peaks of the molecular ion of PCTs. With the help of this method, we detected at least 63 tetra- to nonachlorinated terphenyls in the blubber of a harbour porpoise (Phocoena phocoena) from the North Sea. The interference of these peaks by PCBs ranged from >100 to 0?%. The novel calculation method used in combination with GC/ECNI-MS-SIM is suitable to analyze PCTs in environmental and food samples. However, it can also be applied to GC/EI-MS measurements.