SIMPLE METHOD FOR THE PREPARATION OF WATER-MODIFIED OR METHANOL-MODIFIED CARBON-DIOXIDE AS THE MOBILE-PHASE IN SUPERCRITICAL-FLUID CHROMATOGRAPHY

The polarity range of solutes that can be separated by supercritical fluid chromatography (SFC) can be greatly extended by the addition of polar modifiers to supercritical CO2. In this paper, a new mixing device was introduced, in which highly porous stainless-steel filters were used to generate water-modified or methanol-modified carbon dioxide mobile phases. When supercritical CO2 goes through the mixing device, modifiers held within the small pores of filters can be dissolved in the pressurized supercritical fluids. Among the many stainless-steel filters with different porosities which were tested, 0.5 and 2 mum stainless-steel filters were more effective than the others. To measure the amount of modifiers dissolved in supercritical CO2 after the mixing device, a modifier sensor which consists of a polymer film, i.e. a film of a perfluorosulfonate ionomer (PFSI), was used.