Ambient Pressure Ion Funnel: Concepts, Simulations, and Analytical Performance

Abstract

In mass spectrometry (MS), a major loss of ions can readily occur during their transfer from atmospheric pressure to a lower pressure, which limits performance. Here, we report an ion funnel that can be used to effectively focus ions at ambient pressure (∼777 Torr) to significantly enhance performance in electrospray ionization (ESI) MS. For seven singly charged test ions (m/z 124− 1131), the ambient pressure ion funnel (APIF) is demonstrated to improve ion abundances, sensitivity, and detection limits by up to factors of ∼17, ∼16, and ∼3, respectively, compared to the operation of conventional ESI-MS. Simulated ion trajectories were used to rationalize the enhanced performance of the APIF, which is attributed primarily to using a relatively high RF field amplitude to radially confine ions, a high DC field, and a wide exit ring electrode. The effective focusing of ions at ambient pressures should be beneficial in the future for improving the performance of (i) additional methods that ionize molecules at atmospheric pressure, (ii) ambient pressure ion mobility-based instruments, and (iii) high flow rate liquid chromatography mass spectrometry platforms.

An atmospheric pressure ion funnel with a slit entrance for enhancing signal and resolution in high resolution differential ion mobility mass spectrometry

“…Our group recently reported an ambient pressure ion funnel (APIF) that attaches to the capillary entrance of a commercially available MS to increase the sensitivity of electrospray ionization MS by up to ∼16 fold when compared to the ‘standard’ operation of ESI-MS without the APIF. 26 Thus, the integration of APIF with DMS should also be useful for enhancing the ion transmission efficiency of high resolution DMS-MS.…”

“…27 In particular, the ion trajectory simulation software SIMION has been used for simulating both DMS and APIF instrumentation. 26,28–30 For example, Prasad et al 31 developed a SIMION-based DMS model to enable the accurate prediction of experimental CV values, peak width and ion current for a microscale DMS device. Tang et al 32 used SIMION to develop a DMS model that was shown to experimentally improve the resolution of microscale DMS by focusing ions before entering DMS separation region.…”

“…Tang et al 32 used SIMION to develop a DMS model that was shown to experimentally improve the resolution of microscale DMS by focusing ions before entering DMS separation region. Furthermore, SIMION was also used in our recent work to rationalize the experimental performance of an APIF integrated with ESI-MS. 26…”

Quantification and evaluation of ion transmission efficiency in two‐stage vacuum chamber miniature mass spectrometer

“…19,20 Before entering the mass analyzer, the ions need to pass through the sub-vacuum pre-stage chamber, where the movement of ions is strenuous. An ion funnel can improve ion transmission efficiency, focusing the moving ions radially 21 and reducing ion loss. [22][23][24] Besides, ion transmission efficiency can be improved by using a supplemental electron source inside the skimmer.…”

Multiplexing of Electrospray Ionization Sources Using Orthogonal Injection into an Electrodynamic Ion Funnel

“…35 Ambient-pressure ion funnel systems have also been developed to enhance the transmission of ions. 36,37 Nonetheless, further improvement in the ion current from a single emitter is limited by the smallest droplet size that can be generated at a given flow rate and the maximum amount of charge carried by the ESI droplets, which is known as the Rayleigh limit. 38−40 Multiplexing of the ESI emitters is a promising strategy that has been employed to overcome this limitation.…”