TP391 A high performance OA-ToF mass spectrometer for accurate mass measurement of mobility separated ions
Jason Wildgoose, Martin R. Green, Jakub Ujma, Kevin Giles
Waters Corporation, Stamford Avenue, Altrincham Road, Wilmslow, Cheshire, UK
Introduction
The benefits of coupling time dispersive IMS devices to ToF-MS are well established with instruments utilising these technologies now commercially available. The strength of ToF mass analysers in these geometries is their inherent speed allowing multiple complete mass spectra to be acquired across ion mobility peaks. Whilst the separation timescales of ToF-MS are well suited to IMS, significant challenges exist in conditioning the ion beam for optimum ToF performance whilst maintaining the fidelity of the IMS separation. In addition the temporal concentrating effects of IMS raise significant challenges for the acquisition system. Here, we will present a novel combination of beam conditioning ion optics, ToF geometry and acquisition system that alleviates these issues.
Methods
A novel Q-IMS-ToF instrument has been constructed with the facility to improve mobility resolution by passing ions around a closed loop IMS device multiple times. Downstream of the IMS device is a high pressure gas cell capable of simultaneously collisionally activating mobility separated ions and conditioning the ion beam for optimum ToF performance. The gas cell is an ‘RF only’ quadrupole with a superimposed axial DC field which acts to maintain mobility separation whilst compressing the ion beam ‘phase space’ ensuring good sensitivity versus ToF resolution characteristics. Ion signals are recorded using a novel wide dynamic range ADC acquisition system with enhanced time measuring capabilities.
Preliminary Data or Plenary Speakers Abstract
Preliminary data show that the DC field in the gas cell is capable of maintaining the temporal fidelity of ion mobility peaks with widths <200 µs therefore ensuring arrival time distributions are not distorted/broadened. In addition, the quadrupolar confining potential reduces the ‘phase space’ in the orthogonal direction allowing the generation of ToF-MS peak widths as narrow as 100 ps. This allows ToF-MS resolutions of over 120,000 FWHM to be achieved using a novel ‘offset W mode’ ToF geometry. The gas cell is also shown to produce typical collisionally induced dissociation (CID) efficiencies whist maintaining mobility separation. Calibration to remove the effects of the transit time of mobility separated ions through the gas cell is demonstrated allowing accurate and precise drift time measurements. The analogue-to-digital converter (ADC) acquisition system has enhanced capabilities including potential increases in drift time record length to accommodate the longer cyclic IMS separation timescales and improved timing measurements, reducing the overall ToF system jitter to less than 300 ps. The acquisition system combines two 10bit ADC devices in a novel, dual ADC design which increases the in-spectrum dynamic range by ~60x compared to the previous generation of acquisition system. This allows a linear dynamic range of ~4 orders of magnitude per second to be achieved for signals resulting from mobility separated ions.
Novel Aspect
Novel gas cell, ToF and acquisition system for high resolution and wide dynamic range MS and IMS measurements