Correlation of supercritical fluid extraction with supercritical fluid chromatography in aqueous matrixes

A mathematical model is presented for correlating supercritical fluid chromatography (SFC) in aqueous stationary phases with supercritical fluid extraction (SFE) in aqueous matrixes. A solar coaxial countercurrent chromatography apparatus was used for the SFC and SFE experiments. The SFE extraction vessel, i.e., the column for SFC, was mathematically divided into limited layers. During extraction, each layer was considered to undergo a chromatographic process. The plate heights of all the layers were regarded equal throughout the column because pressure drops in the system were negligible. Each layer's chromatographic capacity factor and peak width were calculated using true SFC experimental data, and the sum of all these peak distributions as a function of time gave the extraction efficiency. Accordingly, the SFE analyte recovery curve could be simulated using SFC data and this model. Since SFC operations are more straightforward than SFE operations, SFE optimization may be more easily achieved using this mathematical correlation. The simulated analyte data of large capacity factors matched the experimental results very well. Deviations gradually became greater as analyte capacity factors were decreased. A rationale is proposed that satisfactorily interprets this deviation trend.