Selective reagent ion – time-of-flight – mass spectrometric studies of cocaine: investigations of charge and proton transfer reaction processes

Abstract Investigations are reported for the reactions of H3O+.(H2O)n (n = 0 and 1), NO+ and O2+• with cocaine (C17H21NO4) using a Selective Reagent Ion-Time-of-Flight-Mass Spectrometer (SRI-ToF-MS) covering a range of DC reduced electric field values (from approximately 60 Td up to about 230 Td), with the electric field strength being determined from the total DC voltage drop across the drift tube. In addition to examining the influence of the reduced electric field value on the reagent ion-cocaine product ion types and distributions, the effects of applying a radio frequency (RF) electric field in the ion funnel region of the drift tube are also reported. Observed reaction pathways without (DC mode) and with (DC + RF mode) the ion funnel operating include non-dissociative and dissociative proton transfer for the reactions involving H3O+.(H2O)n (n = 0 and 1), and non-dissociative and dissociative charge transfer for the reactions involving NO+ and O2+•. Although the dissociative proton transfer pathways leading to product ions with m/z values of 272.129 (C16H18NO3+), 182.118 (C10H16NO2+) and 123045 (C7H7O2+) are highly exoergic, as determined from density functional theory calculations, non-dissociative proton transfer dominates resulting in C17H21NO4.H+ at m/z 304.155. The significance of the lack of dissociative proton transfer is discussed. Non dissociative charge transfer, leading to C17H22NO4+ at m/z 303.155, dominates up to DC drift tube electric field strengths of about 80 V/cm, after which the product ion C5H8N+ becomes the dominant product ion. Other product ions resulting from dissociative charge transfer processes that are common to both NO+ and O2+• reactions with cocaine are C10H16NO2+ and C7H5O+ at m/z 182.118 and 105.036, respectively. The reactions with O2+• lead to a fourth observed fragment ion at m/z 272.129 corresponding to C16H18NO3+.