ABSTRACT
A specially designed mass spectrometer which allows for preparative separation of mixtures is described. This mass spectrometer allows for large ion currents, on the order of nanoamperes, to be produced by electrospray and transmitted into a high vacuum. Accumulation of nanomole quantities of collected and recovered material in several hours is demonstrated. The use of high-velocity ions reduces space charge effects at high ion currents. Separation of mass occurs simultaneously for all ions, providing a 100% duty cycle. The use of a linear dispersion magnet avoids compression at higher m/z ratios. A deceleration lens slows the ions to allow for soft landing at low kinetic energy. The ions are neutralized by ion pairing on an oxidized metal surface. Retractable landing plates allow for easy removal of the separated components.
ABSTRACT
The utility of ion mobility spectrometry (IMS) for separation of mixtures and structural characterization of ions has been demonstrated extensively, including in biological and nanoscience contexts. A major attraction of IMS is its speed, several orders of magnitude greater than that of condensed-phase separations. Nonetheless, IMS combined with mass spectrometry (MS) has remained a niche technique, substantially because of limited sensitivity resulting from ion losses at the IMS-MS junction. We have developed a new electrospray ionization (ESI)-IMS-QTOF MS instrument that incorporates electrodynamic ion funnels at both front ESI-IMS and rear IMS-QTOF interfaces. The front funnel is of the novel "hourglass" design that efficiently accumulates ions and pulses them into the IMS drift tube. Even for drift tubes of 2-m length, ion transmission through IMS and on to QTOF is essentially lossless across the range of ion masses relevant to most applications. The rf ion focusing at the IMS terminus does not degrade IMS resolving power, which exceeds 100 (for singly charged ions) and is close to the theoretical limit. The overall sensitivity of the present ESI-IMS-MS system is comparable to that of commercial ESI-MS, which should make IMS-MS suitable for analyses of complex mixtures with ultrahigh sensitivity and exceptional throughput.
