Development and Application of a Combined Supercritical Fluid Chromatograph with Fourier Transform Infrared Detection

Abstract

The hyphenated analytical methods are among the most powerful techniques available to the analytical chemist for the identification and measurement of the components of complex mixtures. However, current hyphenated methods are mainly centered around gas chromatography (GC), which is applicable only to volatile mixtures. This paper describes the development and application of a relatively new hyphenated method, a supercritical fluid chromatograph (SFC) with Fourier transform infrared (FTIR) detection, or SFC/FTIR. SFC/FTIR is applicable to the separation and identification of nonvolatile mixtures. The mobile phase used here is CO₂ above its critical temperature and critical pressure. The SFC was constructed by using an air amplification type pump, loop injector, packed LC columns, and a high-pressure infrared cell. Design considerations for the high-pressure infrared flow cell are presented. The infrared spectra of CO₂ at a number of pressures are presented. Separation of a mixture of aromatic carbonyls and the infrared spectra of the separated components are shown. Detection limits for the aromatic carbonyls are in the 500-ng range. The SFC/FTIR instrument was also applied to the separation of some nonpolar lipids. Detection limits are in the low microgram range. The utility of CO₂-based SFC/FTIR applied to nonpolar lipid analyses is discussed.