Tandem Mass Spectrometry vs stability of pesticides

The intrinsic stability of a pure standard as well as when diluted in solution has always been a problem for laboratory focused to pesticides analysis. Standards could be very expensive, the official expiry date is too soon, and the time consuming preparation should not be ignored. From laboratory experience, it is well known that many pesticides are stable beyond the expiry date declared by suppliers as well as are the working standard solutions stored in a given solvent and at a given temperature. An useful contribution to define compound stability is recently given by the “Eurl data pool” that collects data from laboratories working in the field of pesticides analysis. The mass spectrometry approach, proposed in this work, was based on MS/MS experiments conducted on some pesticides using a triple quadrupole mass spectrometer (Xevo TQ mass spectrometer; Waters,Milford) and an electrospray as ion source. The measurement of the dissociation of gas phase molecules by collision induced dissociation (CID) tandem mass spectrometry has been an useful approach in the study of the thermodynamic properties of molecules such as bond dissociation energies or their stability. For this reason, some CID fragmentation experiments on molecular ions [M+H]+ of some pesticides have been performed at different collision energies values. These experiments allowed to study both the fragmentation profile and the role of the collision energy in defining the stability of the molecules.