ABSTRACT
In contrast to Gas chromatography, infrared-transparent atomic and homonuclear diatomic mobile phases are inappropriate for high-pressure liquid chromatography (HPLC) and supercritical fluid chromatography (SFC) separations. Unfortunately, infrared absorptions for common HPLC and SFC mobile phases often overlap eluent absorbance bands, making detection and identification difficult. Mixture-component infrared spectra are obtained from flow cell measurements by subtracting mobile phase contributions from acquired spectra. Mobile phases commonly employed for reverse phase HPLC exhibit intense infrared absorptions and are incompatible with Fourier transform infrared spectroscopy detection. Transmission flow cells considered in the previous section are constructed by compressing two infrared-transparent windows about a spacer used to select path length. At each internal reflection, the electric field of the infrared radiation extends slightly into the sample material. A variation of the buffer memory interface in which an infrared microscope is employed for analysis was described by Pentoney et al.
