Characterization and optimization of supercritical fluid chromatography with on-line Fourier transform infrared detection

Abstract

Supercritical fluid chromatography (SFC) has been gaining much exposure over recent years. The characteristics inherent to SFC give it capabilities in separating nonvolatile, thermally labile compounds inseparable by GC, and with greater efficiency per unit time than HPLC. As in the past with the more conventional chromatographic methods, the need for higher information detectors, such as IR, exists for SFC.

The interface of a Fourier Transform Infrared (FTIR) spectrometer to a packed column (analytical scale) SFC is demonstrated. Characterization of mobile phases for SFC-FTIR is presented. Also, parameters for the optimization of spectral sensitivity, such as mobile phase transparency and flow cell design, are discussed. Demonstrations are made via model mixture separations.

Finally, the application of this technique to the analysis of free fatty acids is presented. Identification of carboxylic acids of carbon number 6-18 is made on several standard mixtures and on free fatty acids extracted from various complex samples. The spectral identification of the compounds as free fatty acids is presented, and spectral evidence for dimerization of the acids in CO 2 and the coelution of saturated and unsaturated carboxylic acids is shown.