Determination of pressure–temperature coordinates of liquid–vapor critical loci by supercritical fluid flow injection analysis

Knowledge of phase behavior as sample is transferred through a chromatograph is necessary for the user to either take advantage of desirable effects, such as peak focusing possibilities, or to avoid disastrous peak broadening. Users staying within the norms of conventional chromatographic techniques may not realize the phase behavior events that might be happening or that might be avoided by virtue of the parameter values they use. However, users working with unconventional conditions or with unconventional fluids, such as near-critical or supercritical fluids, must have an awareness of phase behavior through their chromatograph to ensure success. Complete phase diagrams of binary fluids are rare. However, most chromatographic parameters can be set using only knowledge of the temperature and pressure coordinates of the appropriate critical locus. These coordinates can be quickly determined for Type I binary mixtures using chromatographic equipment and a peak-shape observation technique to perform a simple flow injection experiment. Results and chromatographic applications of this knowledge will be summarized.