Counteracting Bleeding in Centrifugal Partition Chromatography: Redosing of the Stationary Phase

Abstract

Centrifugal Partition Chromatography is a type of Liquid-Liquid Chromatography that offers several advantages compared to Liquid Chromatography. Two immiscible liquids are utilized, and one phase has to be immobilized to implement chromatographic separation. This is performed with the help of centrifugal force. As this immobilization is not ideal, the stationary phase continuously leaks out of the apparatus (so-called bleeding). We measured the stationary phase's loss precisely and implemented a controller to compensate for it during operation. This innovative mode of operation is called redosing of the stationary phase and prolongs the experimental runtime significantly. In a first step, we implemented an open-loop controller, which was capable of counteracting bleeding but could not dial to a given setpoint precisely. Therefore, a closed-loop controller with a moving frame shifting factor was programmed. This controller reached and maintained setpoints with high accuracy. The last experimental step was to check for boundaries of this new degree of freedom. In addition, we highlighted the accompanying hydrodynamics during redosing with the help of Computational Fluid Dynamics. We were able to show the influence of different volumes of the redosed stationary phase on the flow regime.

Optimizing Chromatographic Separation with Redosing: Effects on Separation Efficiency of a Model System in Centrifugal Partition Chromatography

“…To investigate the influence of redosing, two worst-case scenarios are considered, i.e., redosing of the stationary phase directly before or after a sample injection. The redosing volumes were chosen to be of a similar order of magnitude to the volumes of redosing volumes in previous investigations [26]. The rotational speed was set to 750 rpm, and the volume flow of the mobile phase was set to 15 mL•min −1 .…”

“…The influence of the retention on the resolution was analyzed for different volumetric flow rates of the mobile phase (5, 10, 15, 20 mL•min −1 ) at 750 rpm and V inj = 0.9 mL. The Sf* setpoint was increased from Sf = 0 to the equilibrium Sf* in steps of 0.1, resulting in the operation points shown in Table 2 [26]. To ensure detection of the samples in the linear range of the detector, concentrations were kept at 200 mg•L −1 per component.…”

“…The operating point for the separation experiments was a volumetric flow rate of the mobile phase of 10 mL•min −1 , a rotational speed of 750 rpm, and concentrations of 200 mg•L −1 for each component to be separated. As discussed in our previous publication, t ctrl should equal six dimensionless residence times of the rotor [26]. Furthermore, after sample injection, t loop is set to 9 min to ensure maximized productivity.…”

“…In conclusion, optimizing the operating point results in the following parameters: a volumetric flow rate of 10 mL•min −1 , 750 rpm, and an Sf* setpoint of 0.72. The setpoint is set slightly below the maximum possible Sf* equilibrium because the setpoint should always be reached within the redosing interval, which makes slight overdosing (induced by the shifting factor) necessary [26]. If the setpoint was set identical to the equilibrium point, this overdosing would not be possible or would be associated with increased solvent consumption without an increase in retention.…”

“…Our recent research focuses on counteracting bleeding by redosing the stationary phase [17,26,27]. Therefore, the amount of stationary phase lost during a specific timespan is redosed into the apparatus repeatedly.…”