Abstract
The coupling of atmospheric pressure ionization (API) sources like electrospray ionization (ESI) to vacuum based applications like mass spectrometry (MS) or ion beam deposition (IBD) is done by differential pumping, starting with a capillary or pinhole inlet. Because of its low ion transfer efficiency the inlet represents a major bottleneck for these applications. Here we present a nano-ESI vacuum interface optimized to exploit the hydrodynamic drag of the background gas for collimation and the reduction of space charge repulsion. Up to a space charge limit of 40 nA we observe 100% current transmission through a capillary with an inlet and show by MS and IBD experiments that the transmitted ion beams are well defined and free of additional contamination compared to a conventional interface. Based on computational fluid dynamics modelling and ion transport simulations, we show how the specific shape enhances the collimation of the ion cloud. Mass selected ion currents in the nanoampere range available further downstream in high vacuum open many perspectives for the efficient use of electrospray ion beam deposition (ES-IBD) as a surface coating method.
Highlights
Electrospray ionization (ESI)[1,2] generates intact molecular ions, which are used for mass spectrometry,[3,4] ion mobility spectrometry (IMS)[5] or for ion beam deposition methods like so landing.[6,7] The coupling of an API source to the mass spectrometer's rst vacuum chamber is usually made via a pinhole, or more frequently through a transfer capillary
Initial tests with a commercial mass spectrometer and with small diameter capillaries showed only small improvements
Key to the enhanced performance of our funnel source is the fact that the nanospray emitter is placed inside of a funnel that constitutes the inlet of a capillary instead of in front of the at cut capillary ori ce. This union of the funnel and the emitter represents a conceptual difference of great importance for the design of atmospheric pressure ion sources: the background gas is an imposition that has to be removed before the ions can be analysed in vacuum
Summary
Electrospray ionization (ESI)[1,2] generates intact molecular ions, which are used for mass spectrometry,[3,4] ion mobility spectrometry (IMS)[5] or for ion beam deposition methods like so landing.[6,7] The coupling of an API source to the mass spectrometer's rst vacuum chamber is usually made via a pinhole, or more frequently through a transfer capillary. The tests with our electrospray mass spectrometer and ion beam deposition experiment[42,43,44] illustrate that the improved performance of the funnel interface has the potential to enhance sensitivity or selectivity as well as sample utilization and throughput[61,62] in mass spectrometry or ion beam deposition applications. Initial tests with a commercial mass spectrometer (i.e. an LTQ Orbitrap) and with small diameter capillaries showed only small improvements.
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