Patent Description:
The object of the invention also relates to a centrifugal partition chromatograph containing such an extraction cell.

The object of the invention also relates to a method for providing such an extraction cell.

Chromatography is the collective name for mixture separation methods based on multistage, high-efficiency, quasi-balance processes, which today, among separation technology processes, has become one of the most frequently used analytical methods. The fields of application include pharmaceutical analysis, foodstuff industry, toxicology and environmental analysis tests.

The basis of the procedure is that the components in a mixture to be separated are distributed in different proportions between a stationary phase and a mobile phase (eluent) flowing through the stationary phase in a specific direction. Using this method the molecules, ions of the components may be selectively separated from each other from solutions with complex compositions. Separation is made possible by that the individual components travel at different speeds while the mobile phase is flowing. This speed depends on the degree of interaction between the component and the stationary phase. Therefore, the components of the mixture travel at different speeds because their distribution between the stationary phase and the mobile phase, in other words their partition coefficient is different.

During centrifugal partition chromatography the liquid stationary phase is kept in place by a strong centrifugal field. In this technique, as seen in the block diagram in <FIG>, the chromatograph contains a liquid pumping system <NUM> serving for feeding the mobile phase <NUM>, a sample feed unit serving for feeding the mixture material <NUM> to be separated, a rotor <NUM> that rotates around an axis, a detector <NUM> and fraction collection system <NUM>. A product <NUM> leaves the system as the final result of the separation process, which preferably contains a single component of the mixture <NUM>. In the rotor <NUM> a network of serially connected extraction cells <NUM> connected to each other by connection tubes <NUM> ensuring liquid connection rotates around the axis of the rotor <NUM>. The separation process takes place in the cascade of series-connected extraction cells containing an inlet and an outlet opening, which are rotated around a common axis at a given speed. As a result of the pumping the mobile phase enters the cell containing the stationary phase through the inlet opening and breaks up into tiny droplets. The resultant of the centrifugal force and the buoyancy will be exerted on the tiny droplets of the mobile phase, due to which the droplets will flow through the stationary phase. The two phases come into contact with each other over a large surface area within the cell. Near to the outlet opening the two phases are separated from each other and the mobile phase leaves the cell.

Coriolis force appears in the reference frame of the cells due to the rotation, as a result of which the path of the mobile phase is diverted. Using liquid simulation methods it can be demonstrated that the Coriolis force reduces the efficiency of the mixing of the two phases, as the diverted droplets run down the sidewall, so reducing the contact interface. The Coriolis force causes circular flow and remixing in the cell, which is a strongly degrading factor from the point of view of separation (see <FIG>).

Various methods may be found in the literature for the production of extraction cells. The Partitron centrifugal partition chromatograph protected by the patent with registration number <CIT> consists of a titanium cylinder, in which the extraction cells and the channels connecting them are produced by milling. A special CNC milling machine is required as the device is milled inside and outside from a single titanium alloy cylinder. The titanium alloy used is very expensive and during machining a large part of the cylinder goes to waste. Therefore the manufacturing of the device is expensive and results in a great deal of waste. The milled channels and cells are connected by covering plates, with flat seals being used between them. The material of the flat seals according to the specification is fluoroelastomer (Viton), which, however, does not tolerate the organic solvents used for cleaning the device well. When they come into contact with these they swell, soften and their sealing ability lessens.

Patent document with registration number <CIT> presents a stacked plate chromatograph in which the network of cells and channels is machined into a stainless steel plate. Teflon sealing plates are to be found between the stainless steel plates, which are punctured at the locations where flow is to take place between the plates. The greatest disadvantage of the arrangement is that the ratio of the useful volume as compared to the total mass of the device is very low, and the machining is expensive, as a great deal of waste is produced during machining. A further disadvantage of the plate arrangement is that due to the Teflon seals used its pressure resistance is low, and after time the Teflon plates become deformed, so reducing pressure tightness. In order to perfectly clean the device it must be completely disassembled, which is complicated and only possible with a press.

The aim of the invention is to provide an extraction cell, a centrifugal partition chromatograph containing such an extraction cell and a method for the production of such an extraction cell that is free of the disadvantages of the solutions according to the state of the art, in other words to be able to provide an extraction cell at a low cost in which the effect of the Coriolis force occurring may be effectively reduced. The aim of the invention is also to provide an extraction cell which may be manufactured so as to cause less waste than the solutions according to the state of the art.

The invention is based on the recognition that the extraction cell may be produced with the help of a tubular body shaped extraction chamber, and a liquid inlet plug and liquid outlet plug connected to its ends, during the production of which less waste is produced and the ratio of useful internal volume/mass is much greater as compared to the solutions according to the state of the art. It was also recognised that an insert that liquid may flow through may be placed in the extraction cell, which effectively reduces the undesirable circular flow in the cell caused by Coriolis force, and the liquid jet of the mobile phase entering the cell more effectively breaks up into droplets upon hitting the insert, due to which the interface between the two phases increases. The objective of the invention is achieved by the process according to claim <NUM> and the extraction cell according to claim <NUM>.

Preferred embodiments of the extraction cell are specified in the dependent claims. The centrifugal partition chromatograph comprising the extraction cell according to the invention is embodied in claims <NUM>-<NUM>. The details of the invention are presented in connection with embodiments, with the help of drawings. In the appended drawings.

The extraction cell <NUM> contains an extraction chamber <NUM> delimited by a cell wall 12c and accommodating the liquid stationary phase 30á, and on its opposing sides it has a liquid inlet opening 13b and a liquid outlet opening <NUM> serving to let in and out the liquid mobile phase <NUM> to be made to flow through the extraction cell <NUM>. The material of the cell wall 12c delimiting the extraction chamber <NUM> is preferably stainless steel, but other materials are also conceivable, such as titanium alloy, aluminium, PEEK (polyether ether ketone), Teflon, etc..

In the case of a preferable embodiment the extraction chamber <NUM> is constructed as a tubular body. This embodiment of the extraction chamber <NUM> is preferably produced using a waste-free production technology, such as 3D printing or injection moulding or metal casting. PEEK is preferably used in 3D printing, but naturally other materials may also be used, as is known to a person skilled in the art.

An insert <NUM> through which liquid may pass is positioned in the extraction chamber <NUM> according to the invention between the liquid inlet opening 13b and the liquid outlet opening <NUM>. In the context of the present invention an insert <NUM> through which liquid may pass means an insert that has internal passages via which liquids are capable of flowing through the insert <NUM>. The average diameter of the internal passages of the insert <NUM>, in other words the average diameter of their cross-section is <NUM>-<NUM> times, more preferably <NUM>-<NUM> times, and even more preferably <NUM>-<NUM> times the average diameter of the mobile phase <NUM> droplets created when the mobile phase <NUM> is made to flow in the stationary phase 30á. The cross-section of the internal passages is not necessarily circular. They may be square, rectangular, triangular or any other irregular plane figure. In this case average diameter may be viewed as the diameter of a circle with an area equal to that of the area of the plane figure.

In the case of a preferable embodiment the insert <NUM> contains one or more elements that liquid may pass through chosen from the following group: wound up net made from metal wire, fibrous woven textile, glass wool, steel wool, although other materials may also be used as is obvious for a person skilled in the art. In a given case the insert <NUM> may be fixed to the cell wall 12c, for example, by gluing, soldering, welding or by other mechanical fixing process. In the case of another exemplary embodiment the liquid inlet opening 13b and the liquid outlet opening <NUM> are dimensioned so that the insert cannot pass through, and due to this it is not necessary to fix the insert <NUM> within the extraction chamber <NUM>.

With respect to its structure the insert <NUM> may have an irregular structure (glass wool, steel wool), a regular structure (metal wire, metal grid), or be a bulk insert. The latter may be realised by using a granulate, spheres, and/or other granular materials.

In the case of an especially preferable embodiment, with the extraction cell <NUM> in its position in the centrifugal partition chromatograph <NUM>, the insert <NUM> is selected so as to reduce the effect of the Coriolis force occurring in the extraction cell <NUM> when in operation.

While providing the insert <NUM> through which liquid may pass, the extraction cell <NUM> is filled with liquid stationary phase 30á, then liquid mobile phase <NUM> is made to flow through the stationary phase 30á in such a way that the mobile phase <NUM> breaks up into droplets when it penetrates the stationary phase 30á. Following this the average diameter of the droplets of the mobile phase <NUM> penetrating the stationary phase 30á and breaking up into droplets is determined. This may take place, for example, by experiment, on the basis of an image recorded of the inside of the extraction cell, or theoretically, with the help of formulae. In a given case the droplets may also have an irregular shape, in this case the diameter of a droplet may be defined as having the same diameter as sphere with the same volume as the droplet. In the case of a preferable embodiment the average diameter of the droplets of the mobile phase is determined on the basis of the Stokes' law. During this the droplets inside the extraction cell <NUM> are considered to be spherical, the average diameter d of which may be calculated, with good approximation, using the following formula: <MAT> where v is the velocity of the mobile phase <NUM> penetrating the stationary phase 30á as compared to the stationary phase 30á, η is the viscosity of the stationary phase 30á, Δρ is the absolute value of the difference in density between the stationary phase 30á and the mobile phase <NUM>, ω is the angular velocity of the rotation of the extraction cell <NUM>, and R is the distance of the extraction cell <NUM> from the axis of rotation. Naturally other relationships may be used to calculate the average diameter of the droplets apart from the above formula, as is obvious to a person skilled in the art.

By using the information obtained about the average diameter of the droplets, an insert <NUM> through which liquid may pass is provided that has internal passages, and the average diameter of the passages is <NUM>-<NUM> times, preferably <NUM>-<NUM> times, even more preferably <NUM>-<NUM> times the average diameter of the droplets.

In the case of a preferable embodiment an insert <NUM> is provided of a size so that its volume is <NUM>-<NUM>%, preferably <NUM>-<NUM>%, even more preferably <NUM>-<NUM>% of the volume of the extraction cell <NUM>. The volume that the insert <NUM> fills in the context of the present invention is the ratio of the net volume of the insert <NUM> and the internal volume of the extraction cell <NUM>, where the net volume of the insert <NUM> is equal to that volume of liquid a completely immersed insert <NUM> would push out of a completely filled vessel.

The insert <NUM> presented above may be produced, for example, from a wound up net of metal wire, fibrous woven textile, glass wool, steel wool and from similar products, or a combination of them.

As a result of the effect of the insert <NUM> the circular flow of the liquid mobile phase <NUM> entering the extraction chamber <NUM> is reduced, as due to its viscosity a large amount of force is required for its to pass through the internal passages of the insert <NUM>, which represent a braking resistance to the flow. This braking resistance is always opposite to the direction of movement of the liquid, and its extent is comparable to, or in a given case greater than, the extent of the Coriolis force occurring in the extraction cell <NUM>, and in this way it reduces or completely extinguishes its effect. As the mobile phase <NUM> is driven by the difference between the centrifugal force and the buoyancy, which resultant force is greater than the Coriolis force, the mobile phase <NUM> entering the liquid inlet opening 13b can continue to flow through the extraction chamber <NUM> all the way to the liquid outlet opening <NUM>, through which it leaves the extraction chamber <NUM> (see <FIG>).

A further preferred characteristic of the insert <NUM> is that the liquid jet of the mobile phase <NUM> entering the extraction chamber <NUM> filled with stationary phase 30á more effectively breaks up into droplets when hitting the insert <NUM>, and significantly ripples after passing through the insert <NUM>. Due to this effect the mixing between the mobile phase <NUM> and the stationary phase 30á improves, and the transfer surface between the two liquids increases.

In the case of a preferable embodiment one or more pits <NUM> ensuring the securing of the extraction cell <NUM> to the external supporting structure <NUM> (see <FIG>) are established on the external surface of the cell wall 12c of the extraction chamber <NUM>.

In the case of an especially preferable embodiment the extraction cell <NUM> can be attached to the extraction chamber <NUM>, it contains the liquid inlet plug 16b according to <FIG> which includes in it the liquid inlet opening 13b and the liquid outlet plug <NUM> according to <FIG> which includes in it the liquid outlet opening <NUM>. In this case the liquid inlet opening 13b is established in the inlet plug 16b, and the liquid outlet opening <NUM> is established in the liquid outlet plug <NUM>. The liquid inlet plug 16b and/or the liquid outlet plug <NUM> are fixed to the cell wall 12c of the extraction chamber <NUM> preferably with a releasable connection, such as a screw thread. Naturally other releasable fixing methods (such as clasp fixing), or non-releasable fixing methods (such as welding, soldering, gluing, riveting, etc.) may be used, as is known to a person skilled in the art.

In a given case, an embodiment may be conceived in the case of which the liquid inlet opening 13b is established in the liquid inlet plug 16b and the liquid outlet opening <NUM> is established in the cell wall 12c, or vice versa, in other words the liquid outlet opening <NUM> is established in the liquid outlet plug <NUM> and the liquid inlet opening 13b is established in the cell wall 12c. The liquid inlet plug 16b and the liquid outlet plug <NUM> are preferably made from one or more of the following list of materials: stainless steel, titanium alloy, aluminium, PEEK, Teflon. The liquid inlet plug 16b and the liquid outlet plug <NUM> may also be made using one of the previously presented waste-free production technologies, and/or using other material working technologies (such as milling, grinding, drilling, etc.).

The longitudinal and lateral cross-sections of a liquid inlet plug 16b that consists of a single part can be seen in <FIG>. In the case of a preferable embodiment the inlet plug 16b leading the mobile phase <NUM> into the extraction chamber <NUM> is established as a cylindrical body, on the side of which facing the internal space of the extraction chamber <NUM> there is a thread <NUM> formed on the outside, such as an external NPT(F) <NUM>/<NUM>" thread. In the case of this embodiment the extraction chamber <NUM> is established in the form of a tubular body, and at least at the one end of the tube on the internal surface there is also a thread <NUM>' established, such as an NPT(F) <NUM>/<NUM>" thread, into which the NPT(F) <NUM>/<NUM>" thread <NUM> of the inlet plug 16b may be screwed. An external thread <NUM> is established at the other end of the inlet plug 16b, such as a <NUM>/<NUM>-<NUM> UN thread. Preferably a hexagonal nut formation may be found between the NPT(F) <NUM>/<NUM>" and the <NUM>/<NUM>-<NUM> UN threads <NUM>, <NUM>, which when held with a standard fork spanner the thread <NUM> of the inlet plug 16b may be easily driven into the thread <NUM>' of the extraction chamber <NUM>.

In the case of a preferable embodiment the liquid inlet opening 13b of the inlet plug 16b contains one or more slanted bores 17f that divides the liquid flowing through it into several liquid jets (see <FIG>). In the case of an exemplary embodiment the diameters of the bores 17f are between <NUM> and <NUM>, but naturally different diameters may also be conceived. The role of the bores 17f is to divide the jet of mobile phase <NUM> liquid into several parts and to spray it evenly into the extraction chamber <NUM>. The division may take place into any optional number of branches, however, when producing the bores it is preferable if the following aspects are taken into consideration:.

According to liquid simulation tests dividing the mobile phase <NUM> into several liquid jets has a positive effect on the flow pattern, as atomisation is improved, or, in other words, the interface between the two phases increases, which is especially desirable from a chromatography point of view.

In the case of an exemplary embodiment the outlet plug <NUM> is also tubular, which, however, preferably contains a single branched liquid outlet opening <NUM>, and conical machining <NUM> is formed on its side facing the internal space of the extraction chamber <NUM> (see <FIG>).

Similarly to the inlet plug 16b, on the side of the outlet plug <NUM> facing the internal space of the extraction chamber <NUM> there is an external thread <NUM> formed on the outside, such as an NPT(F) <NUM>/<NUM>" thread, and on the other side there is an external thread <NUM> formed on the outside, such as a <NUM>/<NUM>-<NUM> UN thread. The outlet plug <NUM> may also be fixed into the thread <NUM>' of the extraction chamber <NUM> using the external NPT(F) <NUM>/<NUM>" thread <NUM>. The connection tube <NUM> visible in <FIG> may be connected to the external <NUM>/<NUM>-<NUM> UN thread <NUM> of the inlet plug 16b and outlet plug <NUM>, with the help of which a liquid connection may be realised between the liquid outlet opening <NUM> of an extraction cell <NUM> and the liquid inlet opening 13b of another extraction cell <NUM> connected in series with it.

The purpose of the conical machining <NUM> is for the droplets of the mobile phase breaking up into droplets which pass through the extraction chamber <NUM> to easily combine, and due to this only the mobile phase <NUM> leaves through the liquid outlet opening <NUM>.

In the case the extraction chamber <NUM> has a larger tube diameter, the liquid inlet plug 16b and/or the liquid outlet plug <NUM> are constructed from several parts that may be separated from each other, as can be seen in <FIG>. In the case of this embodiment the liquid inlet plug 16b contains an inlet truncated cone element 19b responsible for the division of the liquid jet of the mobile phase <NUM> and for sealing, a cylindrical body <NUM> fitted to it, and a threaded cap <NUM> fixing the cylindrical body <NUM> to the extraction chamber <NUM>. The material of the inlet truncated cone element 19b is preferably PEEK, but apart from this it may be made of Teflon, HDPE or other material that is easily machined. The cylindrical body <NUM> is preferably made from ANSI <NUM> stainless steel, but it may also be from titanium alloy, aluminium, PEEK, Teflon, etc., as is obvious for a person skilled in the art.

In the case of a preferable embodiment four branches are formed by milling in the inlet truncated cone element 19b, and three bores 17f branch off each branch, as can be seen in <FIG>. Therefore, there are a total of twelve bores 17f located in the inlet truncated cone element 19b, through which the mobile phase <NUM> gets into the extraction chamber <NUM> after being evenly divided. A section of internal surface of the cell wall 12c at the side towards the liquid inlet opening 13b is etched, which is followed by a conically shaped machined section into which the inlet truncated cone element 19b fits so as to form a seal.

The cylindrical body <NUM> contains a base part 19t that is drilled through in the centre and fits into the internal machining of the extraction chamber <NUM> and a hollow stem 19sz fixed to the base part 19t, as can be seen in <FIG>. The inside of the stem 19sz includes a <NUM> degree conical part <NUM> and a <NUM> depression, a thread <NUM> is preferably formed on its exterior surface, such as a <NUM>/<NUM>-<NUM> UNC thread, with the help of which the connection tube <NUM> may be fixed to the stem 19sz.

In the case of this embodiment a fine M60x3 metric thread is formed on the external surface of the cell wall 12c, at both ends of the cylindrical body shaped extraction chamber <NUM>, onto which the threaded cap <NUM> may be screwed. The edge of the threaded cap <NUM> screwed onto the extraction chamber <NUM> fixes the inlet truncated cone element 19b and the cylindrical body <NUM> located in the extraction chamber <NUM>. The material of the threaded cap <NUM> is preferably strong steel.

An embodiment is also conceivable in which the inlet truncated cone element 19b and the cylindrical body <NUM> are fixed to the extraction chamber <NUM> with the thread formed on the external surface of the cylindrical body <NUM> and the thread formed on the internal surface of the cell wall 12c. In this case it is unnecessary to use a threaded cap <NUM>. The screwing in of the cylindrical body <NUM> preferably takes place using the hexagonal nut formation established on the cylindrical body.

The construction of the liquid outlet plug <NUM> according to <FIG> differs from that presented above to the extent that instead of an inlet truncated cone 19b it contains an outlet truncated cone <NUM>, on which a single branch liquid outlet opening <NUM> and conical machining <NUM> facing towards the internal space of the extraction chamber <NUM> are formed.

<FIG> illustrates a module <NUM> of a rotor <NUM> according to the invention, which contains several extraction cells <NUM> connected in series with connection tubes <NUM>. In the case of this embodiment the module <NUM> also includes in itself the supporting structure <NUM> that fixes the extraction cells <NUM> to the module <NUM>. The module <NUM> is preferably fixed to the rotor <NUM> in a releasable way, such as by using screws. The supporting structure <NUM> is preferably of high strength and has a light, grid-like or net-like structure. The supporting structure <NUM> may be constructed from, for example, metal, metal alloy, plastic, other composite, etc., as is obvious for a person skilled in the art. The extraction chamber <NUM> is fixed to the supporting structure <NUM> using one or more pits <NUM> formed in the external surface of the cell wall 12c, preferably in a releasable way. Naturally, the extraction cells <NUM> may be fixed to the supporting structure <NUM> in other releasable or non-releasable ways, apart from the fixing with the pits <NUM>.

<FIG> illustrates a disc rotor <NUM> with an annular cross-section constructed using the modules <NUM> presented in <FIG>. This embodiment of the centrifugal partition chromatograph <NUM> has a modular structure made up of substantially identical modules, in the case of which each of the modules <NUM> contains one or more extraction cells <NUM> connected with connection tubes <NUM> ensuring a liquid connection between them.

Around the circumference of the rotor <NUM> the modules <NUM> are connected in series with connection tubes <NUM> in such a way that the liquid input of a selected module <NUM> is preferably connected to the liquid input at the main axis of the rotor <NUM> through a feed tube <NUM>, while the liquid output of the neighbouring module <NUM> is preferably connected to the liquid output at the main axis of the rotor <NUM> through a discharge tube <NUM>'.

In the following the operation of the extraction cell according to the invention and of the centrifugal partition chromatograph <NUM> containing the extraction cell <NUM> is presented.

Before separation the extraction cells <NUM> are at least partially filled with liquid stationary phase 30á, then the rotation of the rotor <NUM> along with the extraction cells <NUM> is started. Following this the pumping of the mobile phase <NUM> through the series-connected extraction cells <NUM> is started and as a consequence of the rotation centrifugal force occurs in them. This centrifugal force immobilises the stationary phase 30á, in other words it keeps the stationary phase 30á in the cells. Subsequently, the mixture to be separated is added to the mobile phase <NUM> with the sample input unit, preferably in impulse-like doses.

The direction of the pumping is selected as follows depending on the relationship between the densities of the stationary phase 30á and the mobile phase <NUM>:.

Due to the pumping the mobile phase <NUM> enters the extraction cell <NUM> via the liquid inlet opening 13b, then breaks up into tiny droplets in the stationary phase 30á. In an ideal case the distribution of the droplets is homogenous inside the extraction chamber <NUM>. The insert <NUM> placed in the extraction chamber <NUM> further improves the homogenisation.

Coriolis force is created in the extraction cells <NUM> of the rotating rotor <NUM> as a result of the rotation, which endeavours to displace the flow of the mobile phase <NUM> entering the extraction chamber <NUM> in the sideways direction. The insert <NUM> exerts resistance with respect to the flow, which resistance is comparable to the extent of the Coriolis force, thereby significantly reducing its effect. As the difference between the centrifugal force and the buoyancy is exerted on the mobile phase <NUM>, which resultant force is greater than the Coriolis force, the mobile phase <NUM> entering through the liquid inlet opening 13b is able to flow through the extraction chamber <NUM> containing the insert <NUM>. In an ideal case the two phases are in contact with each other from the liquid inlet opening 13b all the way to the liquid outlet opening <NUM>. The mobile phase <NUM> and the stationary phase 30á become separated in the proximity of the liquid outlet opening <NUM> due to the conical machining <NUM> and the effect of the difference in density between the two phases. The phase with lower density is driven by buoyancy towards the liquid inlet opening 13b, while the denser phase continues to be moved towards the liquid outlet opening <NUM> due to the greater centrifugal force being exerted on it. In an ideal case only the mobile phase leaves the extraction cell <NUM>. The processes presented above are carried out and repeated in each of the series-connected cells <NUM>. If the mixture to be separated is added to the mobile phase <NUM> (preferably intermittently), then the components characterised by different partition coefficients are separated from each other in the extraction cells <NUM>.

In the case of a preferable embodiment several series-connected extractions cells <NUM> form modules <NUM> that may be individually removed from the centrifugal partition chromatograph <NUM>. One of the greatest advantages of the modular construction is that in the case of a single extraction cell <NUM> becoming faulty (blocked, for example) the extraction cell <NUM> can be easily repaired or replaced, furthermore, the periodical cleaning of the extraction cells <NUM> is also simpler to perform. In the case of those embodiments in which the liquid inlet opening 13b and the liquid outlet opening <NUM> are formed in the inlet plug 16b and the outlet plug <NUM>, the cleaning of the extraction cells can be simply performed by unscrewing the plugs, as opposed to the solutions according to the state of the art, in which the entire device has to be dismantled to do this.

Claim 1:
Method for providing extraction cell used in a centrifugal partition chromatograph (<NUM>), during which:
- serially connected extraction cells (<NUM>) are provided that are connected to each other by connection tubes (<NUM>),
- the extraction cells (<NUM>) are filled with liquid stationary phase (30á),
- liquid mobile phase (<NUM>) is made to flow through the stationary phase (30á),
characterised by that:
- the average diameter of the droplets of the mobile phase (<NUM>) breaking up into droplets and penetrating the stationary phase (30á) is determined using the following formula: <MAT> where v is the velocity of the mobile phase (<NUM>) penetrating the stationary phase (30á) as compared to the stationary phase (30á), η is the viscosity of the stationary phase (30á), Δρ is the absolute value of the difference in density between the stationary phase (30á) and the mobile phase (<NUM>), ω is the angular velocity of the rotation of the extraction cell (<NUM>), and R is the distance of the extraction cell (<NUM>) from the axis of rotation,
- an insert (<NUM>) through which liquid may pass through is arranged in the extraction cell (<NUM>), said insert (<NUM>) having internal passages whose diameter is <NUM>-<NUM> times, preferably <NUM>-<NUM> times, even more preferably <NUM>-<NUM> times the average diameter of the droplets.