Stationary Phase Retention in CCC: Modelling the J‐Type Centrifuge as a Constant Pressure Drop Pump

Abstract

To be able to design a J‐type centrifuge for a given need, a method of being able to predict peak elution is required. Predicting peak elution will also allow the user to optimise the process parameters for his or her needs. Such predictions require an accurate knowledge of the volume of the stationary phase retained in the coil for a given set of operating conditions. This paper builds upon an experimental relationship in that the stationary phase retention decreases proportionally to the square root of the mobile phase flow rate. Combining this experimental relationship with the hypothesis that the pressure drop across a coil is independent of mobile phase flow rate, and assuming that the mobile phase flow is laminar, the equation below is derived:

Experimental evidence is presented supporting the above equation. The experimental evidence was gained using, a heptane–ethyl acetate–methanol–water (1.4:0.1:0.5:1) v/v phase system, in normal phase mode using three helical stainless steel coils. These stationary phase retention studies allowed the above equation to be tested under conditions of different rotational speeds and tubing internal diameter. The derived stationary phase retention characteristics from each retention study allowed pressure drop and Reynolds number data to be calculated. The pressure drop data shows that the pressure drop across a coil is constant and independent of the mobile phase flow rate.

Keywords:

• Countercurrent chromatography
• Theory
• J‐type centrifuge
• Liquid stationary phase retention
• Constant pressure drop pump
• Archimedean forces
• Density difference

Notes

^aAn accuracy of 3 mL is used as it allows for small inaccuracies caused by evaporation, spillages, and wetting of surfaces above the meniscus in measuring cylinders.

^bThe stationary phase is displaced from a coil by the mobile phase; therefore the volume of mobile phase in a coil (V _m ) equals the volume of stationary phase displaced from a coil.