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Home arrow Engineering arrow Manipulation and Characterization of Electrosprayed Ions Under Ambient Conditions: Methods and Instrumentation



The control and analysis of ions is most commonly performed under vacuum. The physics of ion motion under these pressures is well understood, thus ions may be identified based on their mass-to-charge ratio (m/z) through different mass spectrometry (MS) methods. The discoveries of both the electron by Thomson [1], and of isotopes by Aston [2] were made possible through the manipulation of charged particles by electric and magnetic fields under low pressure conditions. Thomson and Aston would later earn Nobel prizes for their discoveries in Physics and Chemistry, respectively, highlighting the importance of these early studies.

Gas-phase ions have several distinctive properties that are often exploited in analytical and preparative methods. Their charged nature allows them to be precisely manipulated by electric and magnetic fields for control of spatial distribution, kinetic energy, and separated for identification as a result of mass and charge differences. Additionally, gas-phase ions have exceptional reactivity as a result of their charge. Reactions of ions with neutral molecules in the gas phase is unique in that there exists a long range potential interaction and the polarization of the neutral allows for long interaction times for the ion-molecule pair [3]. This effect is exploited for the characterization of ions through reactions that are specific to functional groups present on ions of interest [4], conformational analysis of proteins and peptides [5], and to gain a better understanding of the mechanisms occurring in organic reactions [6].

Aside from its analytical uses, the separation of ions in the gas phase has a long history as a method of purification. The initial case of such a use was the purification of U235 for the first atomic bomb, in which large Calutron mass spectrometers employed magnetic fields to spatial resolve and collect ionized U235 from mixtures containing mostly U238 [7]. Years later, the same principle of MS purification would be applied to organic molecules in the form of ion soft landing (SL). In these experiments, ions are generally generated outside of the vacuum and

© Springer International Publishing AG 2017 1

Z. Baird, Manipulation and Characterization of Electrosprayed Ions

Under Ambient Conditions, Springer Theses, DOI 10.1007/978-3-319-49869-0_1

transferred into a MS for separation. The separated ions are then deposited on surfaces at low kinetic energies (1-100 eV) within the confines of the vacuum system [8]. SL has since been demonstrated for the preparation of protein and peptide microarrays with retained biological activity [9, 10], surface modification through reactive SL [11, 12], and the deposition of monodisperse clusters [13]. Although MS as a preparative methodology has immense benefits due to the selectivity possible, its wide use in the purification of organic molecules has not been adopted. This is mainly the result of inefficient ion production, ion losses, and low material recovery. Namely, ion transfer from an atmospheric pressure ion source into a vacuum system is associated with immense ion losses. Additionally, at higher ion beam densities space-charge has deleterious effects on the resolution of separation as well as causing additional ion loss within the vacuum system.

The work presented in this dissertation is focused on the development different methods and instrumentation designed specifically to control ions in the ambient environment, without the constraints of a vacuum system and to limit associated ion losses involved with their transfer into a low pressure analysis region. Ion motion in air at atmospheric pressure is inherently more complex than under vacuum and experiments were designed to gain a better understanding of the manners in which ions may be controlled under ambient conditions. A combined approach of simulations and experiments is used to address the topics of transfer efficiency, focusing, and analysis of ions produced by electrospray methods.

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