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16 August / September 2016


Injection by Extraction in Preparative SFC; Isolation of Impurities and Natural Products


Geoffrey B Cox PIC Solution Inc, P O Box 191, Media, PA 19065.


Two applications of combined supercritical fluid extraction – supercritical fluid preparative chromatography (extraction-injection or ‘X-Injection’) are illustrated. One is the concentration and isolation of impurities in a sample wherein the impurities are selectively extracted from a mixture and are eluted within the first few injections, thus dramatically reducing the time required for their isolation for subsequent characterisation. The other, the direct isolation of natural products from an organic matrix, arose from this study. Although an extremely rapid and complete isolation of minor components was not feasible due to the kinetics of extraction, this process can be used for the rapid isolation of components of natural materials without separate extraction and separation steps.


A recent paper described the application of extraction-injection in preparative SFC [1]. The advantages of the technique were predominantly due to the dissolution of the samples in the supercritical fluid rather than in the polar component of the mobile phase, as is done conventionally. In such conventional injection, whether made into the mixed solvent stream or into the co- solvent stream alone, there is the likelihood of sample precipitation from solution as the solution in its strong solvent is mixed with the less polar, weaker CO2


– co-solvent


mixture. Such precipitation results either in a momentary pressure increase during the injection process or can result in blocked columns or filters as the sample or some components are deposited. Dissolution in the supercritical mobile phase prevents this deposition. This was achieved by loading the sample coated on a suitable, preferably non-adsorptive, support into an extractor which is used in place of an injection loop. Pressurisation of the extractor with the mobile phase allows dissolution of the sample which is then periodically injected into the column by opening the injection valve for a defined injection time. Additional benefits of the technique were found to be improved peak shapes and the ability to inject large volumes while avoiding the peak distortions and inconvenience frequently experienced with large injection loops.


During the course of this work some anomalies were noted in the chromatograms arising from the first injection in a sequence. The work reported here is the result of investigating these anomalies and the


Figure 1. Extraction-injection chromatogram of warfarin; 1st injection. Blue line: 210 nm; red line 250 nm. Injection time 10 seconds. Other conditions as in experimental section.


Figure 2. Chromatograms of warfarin, 2nd & 3rd injections. Blue line 210 nm, 2nd injection (20 seconds), red line 250 nm 2nd injection; green line 210 nm 3rd injection (30 seconds), black line 250 nm 3rd injection. Other conditions as in experimental section.


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