Theoretical optimization of analyte collection in analytical supercritical fluid extraction

Abstract

SummaryOptimizing the extracted analyte collection step in analytical supercritical fluid extraction (SFE) is of key importance in achieving high analyte recoveries and extraction efficiencies. Whereas the extraction step in SFE has been well characterized both theoretically and experimentally; the analyte collection step after SFE has few theoretical guidelines, aside from a few empirical studies which have appeared in the literature. In this study, we have applied several theoretical approaches using experimental data to optimize analyte trapping efficiency in SFE. A vapour-liquid equilibrium model has been formulated to predict the trapping efficiency for extracted solute collection in a open collection vessel. Secondly, a simple solution thermodynamic model for predicting solute (analyte) activity coefficients in various trapping solvents has been shown to have utility in predicting collection efficiencies. Finally, effective trapping efficiency after SFE using sorbent media is related to the extent of analyte breakthrough on the sorbent-filled trap after depressurization of supercritical fluid. Using experimental data determined via physico-chemical gas chromatographic measurements (i. e., specific retention volumes), we have shown the relationship between analyte breakthrough volume off of the trapping sorbent and volume ofdepressurized fluid through the collection trap. The above theoretical guidlines should prove of value to analysts in designing and optimizing the best conditions for trapping analytes after extraction via analytical SFE.Names are necessary to report factually on available data; however the USDA neither guarantees nor warrants the standard of the product, and the use of the name by USDA implies no approval of the products to the exclusion of others that may also be suitable.

Extraction of boldo (Peumus boldus M.) leaves with supercritical CO2 and hot pressurized water

“…As the solvent ratio increases, the superficial velocity of SC-CO 2 increases, and the external resistance to mass transfer in a thin stationary film near the boldo particles decreases; the end result being an increase in mass transfer rate. However, as this velocity increases beyond an optimal, system-dependent value, ''operational solubility'' values may be influenced by axial dispersion phenomena (Rodrigues et al, 2002) and/or entrainment of solute droplets by the gaseous CO 2 leaving the glass vials (King & Zhang, 2000;Turner, Eskilsson, & Bjorklund, 2002;Waldmann & Eggers, 1991). In our experiments, the total extract yield was 36% higher using 2.12 than 1.51 g/g substrate/min of CO 2 at 50°C and 90 bar.…”

Supercritical fluid extraction: Present status and prospects

“…For the collection of lipid extracts, it would appear that the open vial or sorbent-filled collection vial are most frequently used; the latter frequently employing some type of sub-ambient cooling to retain volatile species. King and Zhang (2000) have modelled solute trapping in a open vessel in terms of the retention efficiency of the analyte being collected and shown that trapping efficiency is related to the relative vapour pressures of the solute (analyte) and the solvent (supercritical fluid). Since CO2 upon decompression has a large fugacity, it is not unusal for the ratio of solvent/solute vapour pressures to exceed 10 3 .…”