Chemical Ionisation TOF (CI-TOF) at York & Leicester Universities for Detection of Ultra-Low Concentrations of Compounds in Air
A vast range of volatile organic compounds (VOCs) are emitted into the atmosphere with differing loadings, volatilities, chemical functionalities and reactivities, but at present these processes are not well understood. Teams at the Universities of Leicester and York in the U.K. are developing new methods for fingerprinting VOCs in air using time-of-flight mass spectrometry, and Kore has provided equipment to assist these research programs.
The Chemical Ionisation Time-of-Flight Mass Spectrometer (CI-TOF) shown here was designed for the Universities of York and Leicester, with the collaboration of Dr. Lucy Carpenter and Dr. Chris Ennis at the Department of Chemistry in York, and Dr. Paul Monks and Dr. Andrew Ellis of the Earth Observation Science Group in the Department of Chemistry at Leicester. The York and Leicester CI sources (independent designs from the two groups) bolt on to the upper flange of the analytical chamber on the left of the instrument. Their ion sources use H3O+ ions to transfer a proton to the atmospheric stream, ionising molecules efficiently and yet minimising the fragmentation of the molecules of interest. Another term for this method is proton transfer reaction (PTR, PTR-MS, PTR-TOF). Thus, a continuous beam of ions emerges from the CI source at low energies, but with a large range of forward angles. Kore has designed matched transfer optics to focus these ions into a TOF source, which then creates short pulses (~10ns duration) at a frequency of ~10kHz. The pulses of ions are then extracted and injected into the reflectron analyser, where the ions are mass analysed.
The aim of the CI source is to create a detectable number of ions from part per trillion levels of contaminants in atmospheric streams. The time-of-flight MS is used to mass analyse these ions and detect the species of interest. A TOF-MS has been used in preference to a quadrupole mass spectrometer, which has only unit mass resolution and can only monitor a single mass channel at any instant in time. A key aspect of the design has been to develop transfer optics and the pulsing system to maximise the sensitivity of detection at the ion detector. Kore successfully commissioned the CI-TOF in June 2003. Contacted recently, Dr. Ellis said:
"Since receiving the instrument in June 2003, we have performed a variety of tests here at Leicester with various front-end ion sources, and so far we are very encouraged by the flexibility and performance out of the Kore instrument."
Top
Last updated: 10 September 2005 21:21
© Kore Technology Limited 2005