Intermittent counter-current extraction—Equilibrium cell model, scaling and an improved bobbin design

• Equilibrium cell model for intermittent counter-current extraction for continuous injection.
• Improved design of end fittings permitting on-column switching of the mobile and stationary phases.
• On-column switching eliminates the displaced stationary phase seen in the fractions.
• 6% reduction in the retention time of compounds and improved resolution.

This paper describes an equilibrium cell model for intermittent counter-current extraction that is analytically solved for the first time for continuous sample injection between a pair of columns. The model is compared with practice for injections of a model mixture of compounds on a standard high-performance counter-current chromatography instrument giving good agreement for compound elution order and the times to maximum concentration for the eluted components. An improved design of end fittings for the counter-current chromatography bobbins is described which permits on-column switching of the mobile and stationary phases. This on-column switching successfully eliminates the displaced stationary phase seen in fractions when operating ICcE with standard flying leads and gives a 6% reduction in the retention time of compounds and improved resolution due to the elimination of the time delay required to pump the previous mobile phase from standard flying leads.