Resistively heated columns for liquid chromatography
thesisposted on 22.06.2010, 08:01 by Fiona Harvey-Doyle
Interest in temperature as a modifier in HPLC separations has increased markedly recently due to miniaturisation, new stable hybrid stationary phases and the use of superheated water as an eluent. However, for decades temperature has generally been regarded as a parameter that should be kept constant in LC separations for retention reproducibility but there is now a mountain of journal papers supporting the use of this variable. Currently, the limit of implementation usually arises from the lack of LC ovens on the market capable of high temperature applications. This led to the development of a resistively heated LC oven which allowed rapid reproducible heating/cooling patterns of RP columns thus reducing equilibration times and realising high sample throughput. The main objective was to drive temperature programming to a new extreme by rapid column heating akin to GC rather than LC, the emphasis being to produce much sharper peaks very rapidly. It was hoped that temperature gradients could replace solvent gradients and extend the applicability of temperature-programming for hyphenation to other forms of detection. New column materials were sought and tested against high speed temperature gradients. This coupled with micro-column technology should reduce analysis time and appreciably limit the amount of solvent waste currently being generated by conventional LC techniques. The column heating was achieved by two system components, the oven and the eluent pre-heater unit both based on resistive heating. Post-column cooling prior to detection minimised baseline disturbances imposed by a temperature gradient and enabled the use of detection modes such as MS, RI and ELSD as well as UV spectroscopy.