SFC Instrument Modification to Allow Greater Flexibility in Method Development by Generating Mixtures of Solvents and Modifiers On-Line for Mobile Phase B Optimization

Abstract

A binary supercritical fluid chromatography (SFC) system was further modified by the addition of a quaternary HPLC pump. The flow outlet of this pump was connected to the flow inlet of the existing modifier pump (“pump B”) by way of a custom-designed reservoir in such a way that blends of methanol with up to three additional solvents and/or additives could be delivered to pump B on-the-fly. Small amounts of modifiers (0.1–5 %) are typically mixed with mobile phase B in SFC to improve either the peak shape or to optimize the selectivity of the separation. As the critical influence of these modifiers on the separation of complex mixtures cannot a priori be predicted, incremental changes in mobile phase B compositions typically have to be evaluated on a trial-and-error basis. The instrumental modifications described in this paper eliminate the need to prepare these combinations off-line and the concomitant time requirement to re-purge supply and de-gasser solvent lines with each change in composition. By eliminating these steps, a significantly decrease in the overall SFC method development time can be achieved. Furthermore, such an on-line arrangement allows for greater flexibility in method development, that is, in the “fine-tuning” of the method once the stationary phase and gradient conditions have been established.