KINETIC-MODEL OF SUPERCRITICAL FLUID EXTRACTION

A comprehensive mathematical model was developed for a packed-tube extractor geometry that can be used to predict removal efficiency versus extraction time for supercritical fluid extraction (SFE) if the same matrix parameters and extraction conditions are known. The model is based on well-established theoretical relationships describing mass transfer kinetics, the chromatographic elution process, and the convolution theorem. The model considers several factors that could potentially contribute to slow extraction rates, including kinetics of desorption, swelling, diffusion of analyte in the organic component of the porous matrix, and fluid/matrix distribution constants. The method can be applied to model both dynamic and static/dynamic SFE techniques, and can be used to investigate analyte-matrix interaction to determine the extraction-rate limiting process. This information can then be used to predict optimum extraction conditions for different types of samples. The model can be extended to predict extraction rates when other types of fluids (gas or liquid) are used to elute analytes from the packed-tube extractor. A fully optimized extraction method based on a packed tube should consider different types of flowing media (supercritical fluid, liquid, gas, or mixtures) to minimize time and cost of sample preparation procedures. © Oxford University Press 1993.