Phase retention control in preparative centrifugal partition chromatography

Centrifugal Partition Chromatography (CPC) is a separation technique based on Liquid-Liquid Chromatography (LLC) using two immiscible liquids as mobile and stationary phases. The latter is immobilized in separation chambers by the application of a centrifugal field. However, due to non-ideal coalescence in the chambers, the stationary phase gradually leaves the rotor over time, a phenomenon known as bleeding. The amount of stationary phase in the rotor, also referred to as retention, plays a key role in the separation performance of CPC applications. In this study, we have developed an online measurement tool that allows quick and easy measurement of retention using a coalescence chamber (CC) and image analysis. The coalescence chamber is connected downstream of the CPC, enabling its use with non-transparent rotors, which is a major advantage over recently proposed methods that need transparent rotors. It now allows to measure the retention inside the rotor during operation and to use this information for its closed loop-loop control via redosing of stationary phase. This results in maintaining the separation performance over prolonged operating times, which is shown by separating salicylic acid and D(+)-carvone over a period of approximately 8 h using a preparative rotor. At the same time, the specific solvent consumption can be decreased by approximately 53 %, when redosing of stationary phase is applied. Moreover, it is shown that the concept can be applied in both ascending and descending mode and for different rotor volumes. Finally, the advantage of redosing during separation is highlighted for systems in which severe bleeding occurs, as demonstrated by the separation of vanillin and coumarin.