Interfacing supercritical fluid solubility apparatus with supercritical fluid chromatography operated with and without on-line post-column derivatization: Determining the solubility of caffeine and monensin in supercritical carbon dioxide

• Supercritical solubility vessel interfaced with supercritical fluid chromatography.
• Method validation using caffeine as a model compound.
• Efficient and rapid derivatization reaction in supercritical media.
• Supercritical fluid chromatography using post-column derivatization.
• Rapid on-line determination of monensin solubility in supercritical carbon dioxide.

An interface has been developed that enables the direct coupling of a continuously stirred high pressure vessel with on-line supercritical fluid chromatography (SFC). The system provides a rapid means to determine the solubility of organic compounds in supercritical fluid carbon dioxide (SF-CO2). The method involves increasing the loaded vessel pressure in controlled steps to produce a series of progressively more saturated sample solutions for on-line SFC solubility measurements. The method was validated by obtaining mole fraction solubility data for caffeine in SF-CO2 at four different temperatures ranging from 313 K to 343 K through the pressure range 10–28 MPa. For caffeine, SFC detection was performed at 254 nm. The solubility of monensin in SF-CO2 was determined using SFC with post-column derivatization. Vanillin served as derivatizing agent with SFC detection at 520 nm. Mole fraction solubility data for monensin was obtained at 313 K and 328 K through the pressure range 10–27.5 MPa.

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