Mobile Phase and Flow Cell Comparisons in Packed Column Supercritical Fluid Chromatography/Fourier Transform Infrared Spectrometry

Abstract

A comparison of two flow cells which differ in pathlength and flow geometry for Fourier transform infrared (FTIR) detection of separations performed by supercritical fluid chromatography (SFC) is demonstrated. The interfaces employed for the SFC/FTIR experiments are based on the lightpipe design (used in GC/FTIR), but have been modified for work under the relatively high pressures used in SFC. The detection limit for N-methylaniline with 5-mm and 10-mm pathlength cells was found to be as low as 360 ng. Considerations for cell optimization and the consequences of differing pathlengths are discussed. Data are presented on the infrared transparency of CO₂ and methanol-modified CO₂. Work is also described on the use of Freon 23 as a mobile phase for SFC/FTIR. The similar eluting characteristics and complementary infrared window regions of CO₂ and Freon 23 are noted.