Relationship between resolution and analysis time in chiral subcritical fluid chromatography

A model is presented that predicts a defined relationship between chiral SubFC resolution and analysis time. This model is based upon ideal chromatographic behavior and requires column efficiency and selectivity to be independent of mobile phase modifier level and flow rate. The validity of these assumptions was found to be imperfect but acceptable for two model compounds on two commonly used chiral columns. A major implication of the model is that the maximum resolution obtainable with a particular column and mobile phase modifier may be predicted from one injection. The retention time required to obtain a desired resolution is also calculable. This information enables the practitioner to discern quickly the futility of method development efforts. Insufficient maximum resolution predicted from the first injection would require an increase in selectivity to achieve a useful separation. Selectivity may then be altered by temperature, modifier, or stationary phase. The increased column efficiency of SubFC at typical flow rates rescues separations that fail by HPLC, thus shrinking the practitioner's required library of chiral columns. This work demonstrates that SubFC also allows the practitioner to skim through that library very quickly.