Ion Mobility-Mass Spectrometry with a Radial Opposed Migration Ion and Aerosol Classifier (ROMIAC)

Abstract

The first application of a novel differential mobility analyzer, the radial opposed migration ion and aerosol classifier (ROMIAC), is demonstrated. The ROMIAC uses antiparallel forces from an electric field and a cross-flow gas to both scan ion mobilities and continuously transmit target mobility ions with 100% duty cycle. In the ROMIAC, diffusive losses are minimized, and resolution of ions, with collisional cross-sections of 200–2000 Å2, is achieved near the nondispersive resolution of ∼20. Higher resolution is theoretically possible with greater cross-flow rates. The ROMIAC was coupled to a linear trap quadrupole mass spectrometer and used to classify electrosprayed C2–C12 tetra-alkyl ammonium ions, bradykinin, angiotensin I, angiotensin II, bovine ubiquitin, and two pairs of model peptide isomers. Instrument and mobility calibrations of the ROMIAC show that it exhibits linear responses to changes in electrode potential, making the ROMIAC suitable for mobility and cross-section measurements. The high resolution of the ROMIAC facilitates separation of isobaric isomeric peptides. Monitoring distinct dissociation pathways associated with peptide isomers fully resolves overlapping peaks in the ion mobility data. The ability of the ROMIAC to operate at atmospheric pressure and serve as a front-end analyzer to continuously transmit ions with a particular mobility facilitates extensive studies of target molecules using a variety of mass spectrometric methods.

Design, simulation, and characterization of a radial opposed migration ion and aerosol classifier (ROMIAC)

“…This Radial, Opposed-Migration, Ion and Aerosol Classifier (ROMIAC) enables measurement of ions and particles well into the lownanometer regime, with resolution that has enabled mobility separation of peptide stereoisomers (Mui et al 2013). Here, we describe the use of threedimensional finite element simulations in modeling the performance of an instrument capable of probing a wide range (» 600 £) of mobilities (1 to 20 nm in diameter) at select fixed flow rates, and with R as high as »20.…”

“…In this study, we have, therefore, undertaken the design and development of a radial-flow OMAC. This instrument ultimately has important applications for molecular separations as well as for aerosols; it was first applied to molecular ion classification, including the separation of peptide stereoisomers (Mui et al 2013). Hence, it has been labeled the radial opposed migration ion and aerosol classifier (ROMIAC).…”

“…Preliminary measurements were conducted in which ROMIAC1 had either 325-mesh or 200-mesh electrodes, with little difference in transmission efficiency observed; these measurements were also conducted with ROMIAC1 with 500-mesh (25% open area) electrodes, both without and with a hole cut in the outlet electrode (so that particles would not pass through a screen to exit through the outlet port), which also showed little difference in transmission efficiency (see the online supplementary information). The residence time for particles in the ROMIAC is estimated at »0.7 s based on an assumed Q a D 1 lpm and the volumes of the tubing and classification region; measurements associated with, but not reported, in Mui et al (2013) suggested that a coupled ROMIACmass spectrometer showed response times of 90.5 s for a step increase in signal.…”

Charge distribution uncertainty in differential mobility analysis of aerosols

“…HEPA-filtered, particle-free, room air was directed into the charger and the ions exiting the charger were segregated according to their electrical mobility using a Radial Opposed Migration Ion and Aerosol Classifier, ROMIAC (Mui et al 2013;Mui et al 2017), with a TSI 3068 electrometer used for detecting the ions. The measurement covered the mobility range from 0.1 cm 2 V -1 s -1 to 5.9 cm 2 V -1 s -1 .…”

Experimental evaluation of miniature plate DMAs (mini-plate DMAs) for future ultrafine particle (UFP) sensor network

“…Other small-sized DMAs (Brunelli et al 2009;Mei et al 2011;Fern andez de la Mora and Kozlowski 2013;Mui et al 2013), operating at high sheath flow rates, are developed for sizing ions and particles in the diameters less than 10 nm. Parallel-plate DMAs with very short particle classification lengths and operated at high sheath flow rates were also reported in literature for ion sizing and the integration with mass spectrometers (Rus et al 2010;Larriba et al 2011).…”