Mechanism of High Speed CCC

The design of the Type J coil planet centrifuge is schematically illustrated in Figure 4. A cylindrical coil holder is equipped with a gear that is coupled to an identical stationary gear mounted at the central

Figure 4 Design principle of Type J coil planet centrifuge.

Figure 4 Design principle of Type J coil planet centrifuge.

axis of the centrifuge. This gear arrangement produces a synchronous planetary motion of the coil holder, i.e. revolution around the central axis of the centrifuge and rotation about its own axis, both at the same angular velocity and in the same direction as indicated by the arrows. As mentioned earlier, this planetary motion prevents the flow tubes from twisting and, therefore, the system permits continuous elution through the rotating column without the use of a conventional rotary seal device. The coil is directly wound around the holder as shown in the diagram. In practice, a long tube (usually over 100 m in length) is wound around a spool-shaped holder to form multiple coiled layers.

The mechanism of high speed CCC using this centrifuge design is illustrated in Figure 5, where all coils are shown as straight tubes for simplicity. When the coil is filled with two immiscible solvent phases and subjected to the planetary motion, the two phases are distributed in the coil in such a way that one phase (head phase) entirely occupies the head side and the other phase (tail phase) occupies the tail side (Figure 5A). This unilateral hydrodynamic distribution of

Sample feed

Figure 5 Mechanism of high-speed CCC. (A) Bilateral hydrodynamic equilibrium in a closed coil. (B) One-way elution modes. (C) Dual countercurrent system.

Sample feed

Figure 5 Mechanism of high-speed CCC. (A) Bilateral hydrodynamic equilibrium in a closed coil. (B) One-way elution modes. (C) Dual countercurrent system.

the two phases clearly indicates that the head phase (white), if introduced at the tail, would travel through the tail phase (black) toward the head, and similarly the tail phase, if introduced at the head, would travel through the head phase toward the tail. The above hydrodynamic trend can be efficiently utilized for performing CCC in two elution modes as shown in Figure 5B. The coil is first filled with the head phase (white) followed by elution with the tail phase (black) from the head toward the tail of the coil. Alternatively, the coil is filled with the tail phase followed by elution of the head phase from the tail toward the head of the coil. In either case, the mobile phase quickly flows through the coil and is collected from the other end, leaving a large volume of the stationary phase in the coil. Consequently, solutes locally introduced at the inlet of the coil are separated in a short period of time.

The system also permits simultaneous introduction of the two solvent phases through the respective terminals of the coil to induce a true countercurrent flow of the two phases. This dual CCC system requires an additional flow tube at each end of the coil to collect the effluent and, if desired, a sample injection tube at the middle portion of the coil as shown in Figure 5C. In addition to the liquid-liquid dual CCC, this system provides a unique application to foam separation. In the foam CCC system, gas and liquid phases undergo a true countercurrent flow through a long narrow coiled tube with the aid of the Type J synchronous planetary motion. When the liquid phase contains a surfactant, the above countercurrent process produces a foaming stream that moves with the gas phase toward the tail. The sample mixture introduced at the middle of the column is separated into its components according to their foam affinity; foam active components are quickly carried with the foaming stream toward the tail whereas the remainder is carried in the liquid stream in the opposite direction and collected at the head end of the coil. For samples with a strong foaming capacity such as proteins and peptides (ba-citracin), foam CCC can be performed without the use of the surfactant in the liquid phase.

In addition to the Type J planetary motion described above, some other synchronous planetary motions can produce the unilateral phase distribution (Figure 5A) that can be utilized for performing high speed CCC. Among these, the hybrid systems between Types X and L (see Figure 3) are extremely useful because they can retain a satisfactory volume of the stationary phase for viscous polymer phase systems that are used for partition of macromolecules and cell particles.

The hydrodynamic motion of the two solvent phases in the Type J high speed CCC system has been observed under stroboscopic illumination. A spiral column was filled with the stationary phase and the coloured mobile phase was eluted through the column in a suitable elution mode. After the steady-state hydrodynamic equilibrium was reached, the spiral column showed two distinct zones. As shown in the upper diagram in Figure 6, vigorous mixing of the two solvent phases was observed in about one quarter of the column area near the centre of the centrifuge (mixing zone), while two phases are clearly separated into two layers in the rest of the area (settling zone). Because the location of the mixing zone is fixed with respect to the centrifuge system, while the spiral column rotates about its own axis, each mixing zone is travelling through the liquid like a wave of water over the sea, as shown in the bottom diagram in Figure 6. This highlights an important fact: at any given portion of the column the two solvent phases are subjected to a repetitive partition process of alternating mixing and settling at a high frequency of over 13 times per second at 800 rpm of column rotation.

This explains the high partition efficiency attained by high speed CCC. Figure 7 shows a typical separation of flavonoids from sea buckthorn (Hippophae rhamnoides) produced by the standard high speed CCC technique. Major components including isor-hamnetin and quercetin are well resolved within 3 h at partition efficiencies ranging from 2000 to 3000 theoretical plates.

Figure 6 Hydrodynamic distribution of two solvent phases in a rotating spiral column.

Figure 7 Separation of flavonoids from sea buckthorn by the standard high-speed CCC technique. SF, solvent front.

Figure 7 Separation of flavonoids from sea buckthorn by the standard high-speed CCC technique. SF, solvent front.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

Get My Free Ebook


Post a comment