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worked their way through some of the less attractive phases, such as pentane at 200 °C, and it was clear that carbon dioxide was the way to go. Although there were initially some novel developments at Hewlett Packard in the USA on packed columns, they didn't follow it up. At that time the publication thrust primarily coming out of the USA was on capillary work but we started with others in Europe in looking more at the packed columns - essentially as an improvement on HPLC


Our first studies in SFC came out of a desire to do LC of essential oils because we wanted to use an FID as they have weak chromophores - so we needed a carbon free eluent. But that study didn't really work as the involatile analytes of interest needed amethanol co- eluent but these studies opened up the use of packed HPLC columns with UV detection.


Once SFC had overcome the sales hype that it would completely replace all LC and GC methods in a few years, practitioners started to understand what it could do well and which analytes were impractical. Because of the “normal” strongly interactive nature of the separation mechanism it rapidly became clear that one particularly successful area would be chiral separations which required good analyte-column interactions to achieve discriminations. As a method it also had the advantage that after the separation the product was generally solvent free and separation on a large/preparative scale was feasible. At that time the instrumentation available could not provide the reproducibility or robustness needed for routine pharmaceutical assay so that the potential speed advantage could not be exploited but in the last few years newer improved systems have become available.


Would you say that it is more important in that it opens up more possibilities for detection? You yourself have stated that SFC with flame-ionisation detection was unfortunately problematic. Can it be used very easily with super-heated water?


One of the attractions of superheated water (and SFC ) as a liquid phase eluent is that separations can be carried out with the absence of co-solvents, such as methanol or acetonitrile, so enabling organic analytes to be detected without interferences or a high background signal. One obvious detector of interest to anyone with a GLC background is the universal FID but we and a number of other groups have found that the coupling of the two methods presents problems, although we think that our cold nebulisation is potentially successful approach.


One of your publications on super-heated water involved a collaboration with ‘the famed’ I D Wilson in which super-heated heavy water was used in coupling LC to NMR. While this might appear that this was set up just to demonstrate that it could be done, it is a really good idea. Has this approach been taken on by other workers to any great extent?


Superheated water FID trace on a PS-DVB column Figure 2: SFC systemusing amodified Pye 104 oven


As part of our SFC interest we also ran what was probably the first short course on SFC in Europe with speakers from the UK, Europe, Japan and the USA. This resulted in the first book on Supercritical Fluid Chromatography, which also started the RSC Chromatography Monograph series of which I am the Series Editor and now includes over 20 titles.


Going back to your roots in natural products, much of your early ‘super-critical’ work was on SFE. Did this prove to be just another useful extraction tool or did it transform what you were able to do?


The attraction of SFE was that the extraction solvent could very readily be removed to give a solvent free product but there was always the danger that the expanding gases would blow away the extracted analytes. Our interest was to determine whether the trapping processes could be made sufficiently efficient to compete with alternative methods.


You were doing chiral SFC way back in 1997. Do you think that it is regrettable that SFC now seems so strongly linked with preparative chiral work or do you think that this is a fair reflection of the contribution of SFC to pharmaceutical science?


You were working with superheated water in the 1990s but it is only recently that there has been a widening of interest in LC at extremes of temperature. What do you put this down to? Easier accessibility to suitable equipment? Stable stationary phases? The drive for greater efficiency and selectivity?


There were actually many older studies on high temperature LC by groups such as Greibrokk’s but it never took off probably because the equipment was not available commercially - a problem which continues still. He developed some very efficient separations mainly on capillary columns and of course high temperatures have been used for a long time in polymer analysis and SEC.


I think that one limit on the adoption of high temperature LC, usually greater than 100 °C, has been that somany current chromatographers have never used GC so are afraid of high temperature and worry toomuch about column and analyte stability. However, there are now a number of columns that can be used up to 200-220 °C and relatively few analytes have been found to be unstable.


Much of the emphasis on work using superheated water as a mobile phase has been on the fact that it is ‘clean’ and ‘green’.


This collaboration was a good example of the advantages of attending conferences and that is where the germ of the idea for this work was planted. Ian had the LC-NMR (and LC-MS) and we had the superheated water chromatograph which we could fit in the back of a car and readily transport (and set up). There may be other groups using the method but they are not publishing widely, probably because it needs two instruments and practitioners to come together and as I indicated earlier there is still an industrial reluctance to explore high temperatures.


Of course, there is much more to your research career in chromatography than working at high temperature. You have been involved in the characterisation of LC stationary phases and an advocate of the use of retention indices in LC. In particular you were a leading figure in a European collaboration to look for an EU-standard reversed-phase LC stationary phase. How did you get involved in this project and what was the outcome?


The EU project started at the HPLC meeting in Hamburg when a representative of the EU held an open meeting asking for collaborators but our interest in this area went back to many of our earlier studies on the potential of retention indices (based on alkyl aryl ketones - alkylphenones) in HPLC and studies with the Home Office Research Labs on developing


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