Extensive study on physicochemical properties of polychlorinated biphenyls in a commercial ion trap mass spectrometer, relevance in analytical and environmental chemistry

Polychlorinated biphenyls (PCBs) exist as 209 congeners, consisting of biphenyl molecules, where the number and substitution positions of halogen atoms are known to affect industrial uses, environmental transport mechanisms, distribution, fate, and toxicity. The complexity of the problem requires accurate physicochemical studies of an increasing number of congeners in order to understand the environmental and biological processes at play. This work presents a systematic study on the thermodynamic and kinetic properties of PCBs by quadrupole ion trap mass spectrometry. A clear relationship between structure and behaviour of PCBs in mass spectrometry experiments has been observed. Overall data demonstrate that di-ortho congeners show lower thermodynamic stability and higher fragmentation rate than non/mono-ortho. Congeners follow different fragmentation mechanisms according to the number of chlorine atoms in ortho position of the biphenyl system. Experimental kinetic curves of mono/non-ortho and di-ortho congeners show a strong similarity with classical first order kinetics curves; in particular di-ortho congeners follow a first order consecutive reaction while mono/non-ortho follow a first order parallel reaction. For each studied congener the kinetic constant of reaction (fragmentation) has been determined. Data support environmental levels and biochemical transformations described in literature. The general picture of the PCB behaviour inside a quadrupole ion trap provides the basis for the development of reliable and cost-effective analytical methods to the determination of ultra-low level trace of PCB congeners.