University of Warwick crest Dr. Mark P. Barrow: Research in mass spectrometry

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ESI source incorporating ion conveyor

front end of MMM ion source

Mass spectrometry plays an increasingly significant role in biology, and the need to control and understand the phase transition of biomolecules from the condensed phase to the gas phase becomes ever more important. This is especially true when studying quaternary structures of proteins and when the proteins are present in low abundances. Electrospray ionization (ESI) is one of the most commonly used ionization techniques today and yet it is not uncommon for only 1 part in 105 of the electrospray ion current to be available for mass analysis. There is a need, therefore, to develop an ion transport technique which improves collection and transmission efficiencies with atmospheric pressure ionization sources.

Conveyor waveform

SIMION ion conveyor screenshot

3D representation of the conveyor mode waveform. An enlarged image is available, as is a QuickTime animation.

The "ion conveyor" is a new ion optical device that operates over a wide range of pressures, from atmospheric to relatively high vacuum regions (10-3 mbar), and is ideally suited for application in electrospray ionization (ESI) and nanospray ion sources. The device consists of a series of electrodes, to which a series of alternating potentials are applied, phase shifted with respect to one another. The electrodynamic field created in combination with collisional processes are used to focus, collimate, and convey the ions, even when they initially have a large spread in mass, energy, and position. The result is an ion beam with very low divergence and spread in energy, and an increase in sensitivity with respect to the ion source.

Conveyor mode focusing

SIMION ion conveyor focusing

2D representation of the conveyor mode focusing, with three ions being placed on the left hand side, and leaving the device on the right hand side. An enlarged image is available.

Electrostatic optics do not work in the initial pressure regions of atmospheric pressure ionization sources due to shielding and the large number of collisions with gas molecules. Existing electrodynamic focusing devices rely on the Paul effect to provide radial focusing and distortion of the potential wells to promote propagation of ions through the device. The novel approach here is to use a simple series of alternating potentials to create a travelling wave along the axis of the device. The focusing and collimation of the ion beam stems from the relative residence time of ions in the focusing and de-focusing regions of the travelling "saddle-back" field created. For a given cycle of the applied alternating potential, ions spend a larger period of time experiencing the focusing effect of the saddle-back field resulting in a net focusing effect which can be stronger than that realised from the Paul effect. The combination of the sensitivity of the device and the ability to operate at high pressures (and control collisions) is of special relevance to the study of biological species, such as non-covalent complexes and protein and peptide aggregates.


Related references:

  1. “Electrospray Ionisation Source Incorporating Electrodynamic Ion Focusing and Conveying,” Alex W. Colburn, Mark P. Barrow, Matthew C. Gill, Anastassios E. Giannakopulos, and Peter J. Derrick, Physics Procedia, 2008, 1, pp. 51-60
  2. “The Ion Conveyor: Development and Applications of an Ion Source Incorporating an Electrodynamic Focusing Device for Improved Sensitivity,” Mark P. Barrow, Matthew C. Gill, Alex W. Colburn, Anastassios E. Giannakopulos, and Peter J. Derrick, 17th International Mass Spectrometry Conference, Prague, Czech Republic, August 27th - September 1st, 2006
  3. “The ion conveyor: an intermediate pressure ion focussing and transfer device,” Matthew C. Gill, Mark P. Barrow, Alexander W. Colburn, Anastassios E. Giannakopulos, and Peter J. Derrick, 24th Informal Meeting on Mass Spectrometry, Ustron, Poland, 14th - 18th May, 2006
  4. "The Ion Conveyor: Development and Applications of an Ion Source Incorporating an Electrodynamic Focusing Device," Mark P. Barrow, Alex W. Colburn, Matthew C. Gill, Anastassios E. Giannakopulos, John V. Headley, Kerry M. Peru, and Peter J. Derrick, 18th Annual Tandem Mass Spectrometry Workshop, Lake Louise, Canada, November 30th - December 3rd, 2005
  5. “Non-Covalent Interactions of Vancomycin: Results from Electrospray Ionization and Electrodynamic Ion Transfer Devices,” Alex W. Colburn, Mark P. Barrow, Lewis P. Mark, Anastassios E. Giannakopulos, and Peter J. Derrick, 28th Annual Meeting of the British Mass Spectrometry Society, University of York, September 4th - 7th, 2005
  6. "The Ion Conveyor: A New Ion Optical Device for Improved Focusing and Sensitivity," Mark P. Barrow, Alexander W. Colburn, Anastassios E. Giannakopulos, and Peter J. Derrick, 53rd ASMS Conference on Mass Spectrometry, San Antonio, Texas, June 5th - 9th, 2005
  7. "The ion conveyor. An ion focusing and conveying device," Alex W. Colburn, Anastassios E. Giannakopulos, Peter J. Derrick, Eur. J. Mass Spectrom., 2004, 10, pp. 149-154