WO2006045993A1

WO2006045993A1 - Centrifuge apparatus

Info

Publication number: WO2006045993A1
Application number: PCT/GB2005/001242
Authority: WO
Inventors: David William Hawes; Lee Janaway; Ian Alexander Suterland; Philip Leslie Wood
Original assignee: Dynamic Extractions Limited
Priority date: 2004-10-27
Filing date: 2005-03-31
Publication date: 2006-05-04
Also published as: GB0423876D0

Abstract

In order to facilitate the filling and emptying of centrifuge coils, the embodiments disclosed position the exit from the coil at the radially outermost position at the exit end of the coil The centripetal acceleration causes any liquids present to collect at this point, allowing an inert gas to push said liquids out of the coil and into the exit flying lead or dip tube. In the preferred solution this exit flying lead, dip tube, would be the same as that used when the denser solvent is being used as the mobile phase. An embodiment of dip-tube arrangement for lighter phase mobile phases and denser phase mobile phases provides an elbow (12) junction fitting (10) designed to allow the tube (14) connecting to the flying lead to pass through until its end (16) is immersed in the denser phase. For this purpose, the elbow (12) is provided with a recess (18) to allow the tube tip (16) to be positioned level with the outermost edge of the coil (20} without occluding the fluid passage. There is no mixing of phases on emptying or filling of the coil.

Description

CENTRIFUGE APPARATUS

The present invention relates to centrifuge apparatus and in particular to features of centrifuge coils. The preferred embodiments relate to inlet and/or outlet features of the centrifuge coils suitable, to the retention of a stationary phase and for filling or emptying coils and to other fluid directing elements. The coil of a countercurrent chromatography (CCC) centrifuge is usually firstly filled with the solvent intended to be the stationary phase. Once this has occurred, the centrifuge is spun at its operational speed and the solvent intended to form the mobile phase is introduced into the coil. A mixture of chemicals, called the sample, is injected into the upstream end of the coil. As the sample passes through the coil it is separated into its constituent parts that appear in order from the downstream end of the coil. The proportion of stationary phase in the coil largely determines how well a separation is performed. The best separation requires the maximum amount of stationary phase to be present in the coil for the given mobile phase flow rate. Reducing the stationary phase retention causes the quality of a separation to decrease. The stationary and mobile phases are pumped into the coil from the motionless outside world via lengths of tubing called flying leads. A pair of these leads appears from the centre of the coil and takes either a radial or spiral path outwards to each end of a coil. Traditionally a flying lead is connected to the end of the coil using a standard tube fitting. In the case of a lead with a radial path this fitting could be a 90° elbow. For the spiral path, a simple straight union connector could be used.

These approaches work satisfactorily for coils wound from tubing up to an internal diameter of 1.6 mm. Above this internal diameter the proportion of stationary phase cannot reach the maximum achievable. This is due to the mobile phase continuously washing stationary phase out of the coil because on entering and exiting the coil it has to pass through deeper layers of stationary phase. This can reduce the ability of the coil to perform a separation in a short period of time. Eventually all of the stationary phase can be washed from the coil leaving the coil filled only with mobile phase. Without both stationary and mobile phases present in a coil separations cannot be performed and the coil ceases to function. Contamination of a separation from a previous separation is due to a coil not being completely emptied after the preceding separation. This reduces productivity and is a hazard to the end user of the purified or isolated substance. The removal of contamination requires the coil to be completely emptied after a separation or batch of similar separations. Complete emptying is also required after the coil has been internally washed. Emptying small bore coils relies upon the formation of a meniscus inside the tubing that allows a pressurised inert gas to sweep all the liquid from the coil out through a narrow bore flying lead. To shorten the emptying time, a coil should be rotated in such a way to pump the liquids within it to the exit end of said coil.

Filling and emptying coils can introduce gas bubbles, which need to be removed to improve the stationary phase retention. Initially the coil is filled with only stationary phase. This process continues until no air bubbles are observed leaving the coil from its downstream end. This method of filling can be time consuming increasing cycle times and reducing productivity.

The greater the stationary phase retention, the larger the proportion of stationary phase retained in the coil, the greater the resolution of the separation (alternatively expressed as the higher overall purity of the separation). However, as the bore of tubing used to form the coils of CCC centrifuges increases, the depths of the stratified layers of the lighter and denser solvents also increase. In a traditional coil, the denser solvent when used as the mobile phase has to pass through thicker layers of the lighter stationary phase when entering and leaving the coil, as shown in Figure 2. In doing so a large amount of stationary phase is displaced, reducing the proportion of stationary phase in the coil and reducing the ability of the coil to separate substances. This can also cause the stationary phase to bleed continually from the coil, degrading the quality of the separation with time to the point where a separation may not occur.

The present invention seeks to provide increased stationary phase retention and improved coil filling and emptying and improved coil performance. According to an aspect of the present invention, there is provided a system for filling and/or emptying coils including means for introducing a mobile phase into a coil in the position where it would naturally occupy under the action of the coil's motion. This allows a larger amount of stationary phase to remain in the coil over time creating better separations that remain consistent. In the preferred embodiment, there is provided means for supplying fluid to and/or drawing fluid from a coil including barrier means for preventing supply and/or drawing from the other fluid phase. The barrier means may be one or more portions of an inlet and/or outlet tube, the radial position of said inlet/outlet tube, a weir, a siphon, a valving element or any other suitable element.

The preferred embodiment of inlet and outlet details can maximise the stationary phase retention in coils formed from large bore tubes when either the lighter or denser liquid is the mobile phase.

Advantageously, there are provided inlet and/or outlet connections, which can minimise the displacement of the stationary phase from the coil.

In the preferred embodiment, the inlet and/or outlet connections can be reconfigured to permit either the denser (radially outer) liquid or the lighter (radially inner) liquid to be the mobile phase.

The preferred outlet or exit connection allows the coil to be completely emptied of both the lighter and denser liquids and most preferably that allows the coil to be completely emptied of any liquid used for cleaning and washing of the coil.

According to another aspect of the present invention, there is provided a coil assembly for a centrifuge including a system as specified herein.

According to another aspect of the present invention, there is provided a countercurrent chromatography centrifuge including a system as specified herein.

According to another aspect of the present invention, there is provided a method of filling and/or emptying a coil of a countercurrent chromatography centrifuge including introducing a mobile phase into a coil directly to or withdrawing a mobile phase directly from the position it would naturally occupy under the action of the coil's motion by use of barrier means preventing supply and/or drawing from another fluid phase.

Preferably, the step of introducing a mobile phase or withdrawing a mobile phase occurs during rotation of the coil and centrifuge. Embodiments of the present invention are described below, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows a cross-sectional view of a prior art coil arrangement with the lighter phase being pumped through the coil as the mobile phase.

Figure 2 shows a cross-sectional view of the prior art coil arrangement of Figure 1 with the heavier phase being pumped through the coil;

Figure 3 shows a cross-sectional view of an embodiment of coil arrangement with the heavier phase being pumped through the coil as the mobili phase; Figures 4a and 4b show two views of an embodiment of dip tube arrangement; Figure 5 shows the dip tube arrangement of Figures 4a and 4b for emptying a coil at the outer edge of the coil;

Figure 6 shows an embodiment of inlet and outlet configuration for filling a coil with liquid without trapping air;

Figures 7a and 7b show an embodiment of dip tube arrangement where the flying lead tubingjs used to form the dip tube;

Figures 8a and 8b are schematic diagrams of a combined dip tube and siphon for switching between normal and reverse phase chromatography or switching between emptying and filling;

Figure 9 shows a schematic diagram of an embodiment of tap arrangement for switching between normal and reverse phase, chromatography or switching between emptying and filling;

Figure 10 shows a schematic diagram of another embodiment of tap arrangement for switching between normal and reverse phase chromatography or switching between emptying and filling;

Figure 11 shows a schematic diagram of another embodiment of tap arrangement for switching between normal and reverse phase chromatography or switching between emptying and filling; Figure 12 shows a schematic diagram of another embodiment of tap arrangement for switching between normal and reverse phase chromatography or switching between emptying and filling;

Figure 13 shows how the coils ends could be bent outwards when the denser solvent is used as the mobile phase; and Figure 14 shows an embodiment of method of connecting the flying leads to the appropriate position for either normal or reverse phase chromatography or for filling and emptying.

The inventors have discovered that in coils wound from tubing with an internal diameter, bore, of less than 1.6 mm it is possible for the surface tension of a liquid to form a meniscus across the inside of the tube. This meniscus forms a barrier across the inside of the tubing that when pressurised by an inert gas will push all of the liquid out of the coil. In larger bore tubing it is more difficult for surface tension to form a meniscus and above a critical bore size a meniscus will not form. Without a meniscus some liquid will remain inside the coil causing possible contamination of the next and later separations.

The embodiments disclosed herein position the exit from the coil at the radially outermost position at the exit end of the coil. The centripetal acceleration causes any liquids present to collect at this point, allowing an inert gas to push said liquids out of the coil and into the exit flying lead or dip tube, as shown in Figure 5. In the preferred solution this exit flying lead, dip tube, would be the same as that used when the denser solvent is being used as the mobile phase. However, larger bore flying leads are now being used, making it difficult for the denser solvent to form a meniscus in the flying lead. Again without a meniscus the inert gas cannot completely empty the coil. However, a separate exit flying lead or dip tube could be used with a small enough internal diameter to allow the formation of a series of menisci that can push the mobile phase out of the flying lead while the centrifuge is rotating.

Figures 4a and 4b show an embodiment of dip-tube arrangement for lighter phase mobile phases (Figure 4a) and denser phase mobile phases (Figure 4b). An elbow 12, junction fitting 10, is designed to allow the tube 14 connecting to the flying lead to pass through until its end 16 is immersed in the denser phase. For this purpose, the elbow 12 is provided with a recess 18 to allow the tube tip 16 to be positioned level with the outermost edge of the coil 20 without occluding the fluid passage, as shown by the arrow 22 in Figure 4b.

In an embodiment, two sets of tubes 14 with differing lengths were provided, one for each of the mode of operation shown in Figures 4a and 4b. Each tube 14 is fitted with a "dead-stop" location collar 24 to ensure the correct positioning of its end 16 within the elbow 12, as shown particularly in Figure 4a. Referring now to Figure 5, there is shown the arrangement of dip-tube 14 for empting the coil 22 of both mobile and stationary phases. The arrangement of Figure 5 is similar to that for pumping the denser liquid as the mobile phase of Figure 4b. In this embodiment the coil 22 would be rotated in the anti-clockwise direction. The liquids are represented by light grey hatching shown by arrow A and the pressurised inert gas by the clear space radially inside the light grey hatching shown by arrow B.

When filling a coil with a liquid A, the inlet at the upstream end of the coil is positioned at the outer edge of a coil 20, as shown in Figure 5. Also the dip tube 14 is positioned to fill the tubing 20 at its outermost radial position. This stops gas bubbles being trapped at the upstream end of the coil.

At the downstream end of the coil, the dip tube 20' is positioned on the inner edge of the coil, as shown in Figure 6. In Figure 6 the liquid filling the coil is presented by the dark hatching and arrow A, and the gas by the clear region in the tubing and arrow B. This downstream end allows gas to escape through a dip tube 20' or outlet positioned at the most radially inner position. This stops gas bubbles being strapped at the downstream end of the coil 20 .

The combination of these inlets and outlets minimises the time taken to fill coils reducing cycle times and improving productivity.

It will be apparent that many variations of the embodiments described above could be devised. For example, a clamping mechanism could be provided that would permit the position of the dip-tube's end to be optimised for a particular phase combination, its position being indicated by a graduated scale engraved on the tube or a mechanical stop with a number of positions. Thus, the tube 14 would be adjustable within the collar 24 as shown in Figures 4a and 4b.

Figures 7a and 7b show an embodiment where the dip tube 114 is formed by different lengths of flying lead tubing protruding from the fitting 116 used to attach the flying lead to the end 120 of the coil 122. Figures 8a and 8b show a dip tube 214 of a fixed length combined with a siphon

230. The siphon 230 is, in this embodiment, screw-threaded into the coil end member 220 so that it can, by screwing or unscrewing, be moved to accommodate either the denser or lighter liquid as the mobile phase.

In another embodiment, a tap or valve arrangement 330, 430, 530, 630 is be provided in the coil end element 320, 420, 520, 620 to permit changeover without the necessity to disconnect and exchange tubes 114, as shown in Figures 9 to 12. An equivalent tap or valve arrangement could be provided to permit the entry/exit point to be positioned at will within the bore of the coil tube.

If a coil were only ever to be used to pump one of the liquids as the mobile phase (lighter or denser) then the entry/exit points could be arranged accordingly. Alternatively the ends 124 of a coil could be bent outwards as shown in Figure 13. For the denser fluid as the mobile phase the coil ends would be bent outwards. Bending outwards means either allowing the coil ends 124 to be formed by tangents or using a larger bend radius than that immediately adjacent to either coil end. Bending either one or both ends outwards would also allow the coil to be completely emptied.

The end of the flying lead 114, regardless of the material from which the lead was constructed, could form the dip-tube.

A combination of appropriately positioned inlets and outlets would allow both the lighter and denser phases to be pumped through the coil in the same or opposite directions. Another inlet at an appropriate position, possibly half way along the length of the coil, could be provided to allow sample to be injected either discretely or continuously. The dip-tube 114 could be arranged to point inwards instead of outwards.

The inlets and outlets for the denser phase could be positioned on the radially outer most section of the coils tubing. The inlets and outlets for the lighter phase could be positioned on the radially inner most section of the coils tubing. The inlets and outlets could be aligned tangentially at appropriate radial positions for the lighter and denser liquids.

Instead of using a tap or dip tube arrangement, each end 126 of a coil could be connected to a pair of flying leads 118, 128, one positioned to deliver or receive lower phase at the appropriate radial position and the other to deliver or receive upper phase, as shown in Figure 14. Therefore, each coil 120 would be connected to a total of four flying leads. The selection of which flying leads 118, 128 to use, depending upon whether the denser or lighter liquid would be used for the mobile phase or filling or emptying, would be controlled by valves external to the centrifuge (not shown). Additional flying leads may also be attached for emptying the coil through a narrower bore lead as already mentioned or adding a sample in the case when both the lighter and denser liquids are pumped in the same or opposite directions.

In Figure 14 the flying leads 118, 128 are shown at arbitrary angle to the coil tubing 120. These leads 118, 128 could be attached at any other acute, obtuse or reflex angle to the coil tubing. Such angles could include a fluid path that is normal or tangential to the coil tubing. The use of coils wound from tubing greater than 1.6mm bore combined with end details as described allows CCC centrifuges to purify and separate production scale quantities of sample. A 1.6mm bore coil can process up to 1 gram of sample per hour at a mobile phase flow rate of up to 10ml/min. A coil with end details as described wound from 4mm bore tubing processed 25 grams every 35 minutes at a mobile phase flow rate of 80ml/min. Another coil with end details, a 10mm bore was able to process 115 grams of sample per injection every 40 minutes at a flow rate of 400ml/min. This demonstrates that end details allows the stationary phase to be retained in coils with bores greater that 1.6mm at high mobile phase flow rates allowing large quantities of chemical and biochemical substances to be separated in short periods of time.

Claims

1. A system for filling and/or emptying one or more coils of a countercurrent chromatography centrifuge including means operable to introduce a mobile phase into a coil directly to or to withdraw a mobile phase directly from the position it would naturally occupy under the action of the coil's motion, said means including barrier means for preventing supply and/or drawing from another fluid phase.

2. A system according to claim 1, wherein the barrier means is adjustable.

3. A system according to claim 1 or 2, wherein the barrier means is provided by one or more portions of an inlet and/or outlet tube.

4. A system according to claim 1, 2 or 3, wherein said or at least one of said barrier means is provided by one or more flying leads to the coil or coils.

5. A system according to claim 4, wherein the flying lead or leads as arranged so as to be able to be located inside a coil.

6. A system according to any preceding claim, wherein the barrier means includes one or more weirs.

7. A system according to any preceding claim, wherein the barrier means includes one or more siphons.

8. A system according to any preceding claim, wherein the barrier means includes one or more valving elements or tap arrangements.

9. A system according to claim 8, wherein the or each valving element is operable to direct flow of a mobile phase from an inlet to the position said mobile phase would naturally occupy under the action of the coil's motion.

10. A system according to any preceding claim, wherein an outlet or exit connection allows a coil coupled thereto to be completely emptied of both lighter and denser fluids.

11. A coil assembly for a centrifuge including a system according to any preceding claim.

12. A countercurrent chromatography centrifuge including a system according to any one of claims 1 to 10 or a coil assembly according to claim 11.

13. A method of filling and/or emptying a coil of a countercurrent chromatography centrifuge including introducing a mobile phase into a coil directly to or withdrawing a mobile phase directly from the position it would naturally occupy under the action of the coil's motion by use of barrier means preventing supply and/or drawing from another fluid phase.

14. A method according to claim 13, wherein said step of introducing a mobile phase or withdrawing a mobile phase occurs during rotation of the coil and centrifuge.

15. A method of producing production scale quantities of a material by a method according to claim 13 or 14.