Accepted: Scrivens Radical Cation

Introduction

Ion mobility, coupled with infrared spectroscopy, has previously been shown to be able to separate and characterise protomers formed during the electrospray ionisation of benzocaine. The ratio of nitrogen and oxygen protonated species was found to be dependent on the permittivity of the surrounding medium. Studying these species is important for theoretical and practical reasons given their potential appearance in many ESI spectra. The mobility resolution required to separate the protomers of benzocaine was a modest Ω/∆Ω of 40 (where Ω is the rotationally averaged cross section. Here we generate not only protomers of benzocaine but also radical cation species. Use of a cyclic ion mobility-enabled quadrupole time-of-flight instrument has allowed us to resolve and characterise these radical cation species.

Methods

Studies used a cyclic ion mobility-enabled quadrupole time-of-flight (Q-cIM-oaToF) mass spectrometer. The cIM device minimizes instrument footprint whilst providing a longer, higher mobility resolution separation path; a multi-pass capability provides significantly higher resolution over a reduced (selected) mobility range; the cIM device can be by-passed if not required and, the multifunctional ion entry/exit array can select species within a range of mobilities, providing additional functionality. The cIM device consists of a 100 cm path length RF ion guide comprising over 600 electrodes around which T-Waves circulate to provide mobility separation. Ionisation was carried out using both ESI and ASAP approaches. ASAP generates both protonated and radical cation species. Mobility separated species were subjected to CID and fragmentation maps generated.

Preliminary Data

The cIM device was shown to have a resolution Ω/∆Ω of 65 for single pass operation. Protomers formed from benzocaine under both ESI and ASAP ionisation conditions were resolved and CID product ion spectra obtained. The nitrogen protonated species was found to have a more compact conformation (in line with previous work). The radical cation (formed in the same ASAP experiment as the protonated species) was resolved from the protonated species in a single pass and was found to have a cross sectional value which lay between the nitrogen and protonated species. Utilising the multi-pass capability of the instrument the radical cation species was selected and subjected to increasing mobility separation. The loss of sensitivity for each cycle of the device was measured at less than 2%.
After 15 passes through the cyclic device (Ω/∆Ω = 250) the radical cation displayed further structure resolving into two distinct components. These were isolated and subjected to CID at varying collision energies. The fragment maps indicated the presence of two distinct structural species with different fragmentation pathways. These could be rationalised in terms of nitrogen and oxygen charge sites. The rotationally averaged cross sections were measured and compared to the protonated species. Other structurally related compounds were also studied and comparisons made with literature data.

Novel Aspect
Characterisation of ion mobility resolved radical cation species.
Options:

A post-doc is presenting author on this abstract? No
A graduate student is presenting author on this abstract? No
An undergraduate student is presenting author on this abstract? No

Oral Choice:

Ion Mobility: New Developments & Applications
Second Oral Choice:

Ion Mobility: Structure
Poster:

Ion Mobility: Fundamentals

Submitting Author:

James Scrivens
Teesside University
Middlesbrough,
jim.scrivens@gmail.com