THE BETA-DISTONIC ION FROM THE REACTION OF PYRIDINE RADICAL-CATION AND ETHENE - A DEMONSTRATION OF HIGH-PRESSURE TRAPPING IN FOURIER-TRANSFORM MASS-SPECTROMETRY

The adduct ion formed in the reaction of pyridine radical cation and e thene exhibits different chemical reactivities and fragmentation behav ior than the isomeric ethylpyridine radical cations. The most characte ristic features of the adduct ion are the collisionally activated loss of C2H4 to give back the pyridine radical cation and the second ioniz ation to produce a doubly charged ion. A characteristic reaction is wi th dioxygen to form a new adduct, which may have the structure of a di stonic peroxy radical cation. The reactive site for attachment Of C2H4 is the nitrogen atom of the pyridine, giving rise to the beta-distoni c ion adduct, C5H5N+-CH2C.H-2, which can be differentiated from the is omeric alpha-distonic ion, C5H5N+-C.HCH3. Formation of the beta-diston ic ion requires collisional stabilization, and this species cannot be directly observed under conventional Fourier transform mass spectromet ry (FTMS) conditions. Incorporation of a new radiofrequency (RF)-only- mode event in FTMS allows the adduct to be formed and then to be chara cterized under the high-pressure conditions of two of these RF-only-mo de events.