Methods and instrumentation for the manipulation and characterization of electrosprayed ions under ambient conditions
Charged droplets and ions both possess properties which makes their use beneficial for preparative and analytical techniques. Their charged nature makes them amenable to control by electric and magnetic fields and this is regularly exploited for analytical purposes. Gas-phase ions also have unique reactivity, often displaying reaction rates that exceed their solution phase counterparts at both atmospheric and reduced pressures. This property is regularly used inside the vacuum system of mass spectrometers to probe structure and for functional group identification. Plumes of charged droplets are highly dispersive in nature, an asset essential in the production of uniform films and to avoid aggregation in spray synthesis of sub-micron particles. Despite the advantages of ions and droplets for synthetic purposes, there is a lack of systems by which they may be manipulated at atmospheric pressure. Under vacuum conditions, such as those in mass spectrometers and focused ion beam systems, the control of ion trajectory is well understood; however, at atmospheric pressure ions no longer behave in the same manner due to frequent collisions with the background gas. This behavior complicates analysis and makes the precise direction of ions onto surfaces troublesome. The work presented herein was done to explore methods by which ions could be controlled and analyzed under ambient conditions. Spatial focusing of electrosprayed ions at atmospheric pressure by electrostatic fields is demonstrated in several different systems. In some cases this is demonstrated by coupling with a mass spectrometer for analysis of the ions, while in others the systems are used as a standalone analysis and ion-molecule reaction platform. A novel form of ion focusing is also demonstrated in which electrosprayed ions are directed into an annulus with high efficiency. This form of annular focusing is then coupled with an atypical ion mobility spectrometer that functions under ambient conditions without the use of supplementary gas flow or reduced pressures. The use of 3D printing to produce electrodes and components is also explored and the results highlight the utility of fused deposition modeling in the further exploration of ion manipulation and characterization under ambient conditions.
Cooks, Purdue University.
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