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Miniaturised Separation Science Technology for Mass Spectrometry

David Simpson

My research was focused on the development of capillary electrochromatography and its interfacing to mass spectrometry.

Capillary electrochromatography (CEC) can be thought of as a hybrid of capillary zone electrophoresis (CZE) and high performance liquid chromatography (HPLC), utilising electroosmotic flow (EOF) to drive mobile phase through the capillary as in CZE, and packing the capillary with stationary phases similar to those used in HPLC. CEC aims to incorporate the high separation efficiency of CZE with the selectivity and sample capacity of HPLC. EOF arises from the interaction between an electrolyte and a surface, and is superior to pressure driven flow (as used in HPLC) because mobile phase velocity at any particular point is largely independent of the proximity of that point to a surface.

Detection in CEC is most simply achieved using UV-visible absorbance detection, but the small size of the capillaries used (around 0.1 mm in internal diameter) results in relatively poor concentration detection limits. A solution is provided by the combination of an ion trap and a time of flight mass spectrometer (TOF/MS). As analytes are eluted they are first ionised and then stored in the trap before being ejected into the TOF/MS. The ion trap essentially acts as an accumulation stage, improving detection limits, while the TOF/MS provides a fast, pulsed mass analyser.

Ideally the separation column would terminate at the point of ionisation, but it is often convenient to use a connecting capillary. Computational fluid dynamics modelling and laser induced fluorescence imaging has been used to investigate capillary jointing such as that which would be required between a separation column and a connecting capillary. Strategies for the production of improved connections have been identified.