DE1498945A1 - Method and device for chromatographic separation - Google Patents

Description

Method and device for chromatographic separation Priority: USA Serial No. 210642 BC July 18, 1962 The invention relates to a method and a Device for chromatographic separation, in which a substance mixture in Kceislauf a plurality of separation columns is passed.

Chromatography is a named method for separating a3 Mixture of substances into its various components.

Various chromatorraphic eohniken are available to the expert, for example liquid-gas chromacography or partition chromatography, solid-gas or absorption gas chromatography, liquid-liquid and liquid-solid chromatography, As an example of the liquid-gas technology, a separation column of suitable length with a inert material such as brick dust or diatomaceous earth. This material comes with coated with a suitable non-volatile liquid. Through this pillar becomes a Carrier gas such as helium or hydrogen passed. This arrangement thus has a liquid stationary phase and a gaseous moving phase. The liquid phase-fird with regard to the desired separation of a gas or vapor sample to be analyzed selected. The sample, which consists of several components, is incorporated into the occupied carrier stream introduced and flushed by this through the separation column. because the sample through the separation column moves, their constituents become as a result of their different Affinities to the liquid phase delayed differently. from the separation column Then carrier gas emerges, which contains "bands" of the various components that appear after one another at the exit of the separation column and in the separation column towards the exit enr and more are spatially separated from each other0 The above description is something idealized. In practice, it can be quite difficult to identify the various Completely separate materials from each other. For example, break when analyzing Complicated hydrocarbon mixtures have the "lighter" components much earlier through as the "heaviest" components. Between the light and heavy ends of the chromatogram may contain a multitude of very similar components that lie apart only with great difficulty or through the assistance of one unusually long @ racing column can be separated. The terms "light" and "Heavy" here does not necessarily refer to the weight the retention times in the column. The "light" ends are the ones that come first break through, the "heavy" ones; new are those who are most restrained will.

There are limits to the extension of the separation columns, @p apart from The pressure drop also increases with the increased space and material requirements for long separation columns very soon unbearably high in the separation column. "Heavy" components of the mixture have a correspondingly long retention time with very long separation columns, which means the duration of the analysis is undesirably extended.

By the German patent 1 079 352 is an arrangement with three-same or different separation columns known. These columns are connected to each other via multi-way taps. In one switch position of each multi-way valve is the outlet of the upstream separation column with the atmosphere and the inlet connected to the downstream separation column with a carrier gas source. In a second On the other hand, the switch position of the valve is the output from the upstream racing column connected to the input of the downstream 0 The carrier gas stream flows into the Atmosphere. Each of the separation columns has a thermal conductivity detector at its exit, which allows the breakthrough of the various bands to be displayed and recorded. You can first set the teaching way cock in such a way that the carrier gas and the "light" Mix components after passing through the first Trein column initially into the atmosphere be blown off. The associated bands @ can be thermally conductive with the help of the first its cell can be measured and recorded.

If now bands in a selected central area of the chromatogram appear that cannot be sufficiently resolved with the first separation column, then the multi-way valve can be switched over. These components then still flow do not release into the atmosphere but rather take a look at the entrance of the downstream second separation column. Such bands may be produced by this second separation column further resolved, cie not yet completely separated by the first separation column could become. Should bands also not be sufficient in the second separation column are separated, this can easily be added to a third separation column weraen. Finally, the possibility is provided for the XusFan, the oritten separation column again with the entrance of the first separation column to connect so that cycle through certain fractions of the sample several times through the second and third Separation column can be passed.

However, this circulating operation is limited in the known arrangement set, because with further and further resolution it can happen that "lighter" components eventually the "heavy" constituents overtake, i.e. one component that moves relatively quickly through the separation columns, again from the exit of the third Separation column is added to the inlet of the second separation column before a slower one Component has left the second separation column, and finally the slower component catches up. Then the situation is very confusing. You have to get out of this Basically, the separation columns in the known arrangements make and can be relatively long the fraction to be separated does not circulate freely through the separation columns let run. Because of the "heavy" ends of the chromatogram, their retention times can be a multiple of the retention times of the components sought only two of the three separation columns are used for working in the cycle will.

This namely contains the "heavy" components that are very slow-through migrate the separation column so that the appearing at the exit of the third separation column Components cannot yet be traced back to the first column.

The invention is therefore based on the object of a method and to create a device for chromatographic separation, in which with a relatively short separation column length by working in a circuit with any frequent Pass a high separation efficiency can be achieved, and not only in which those mixture components that run faster than a selected fraction, but also those who move more slowly through the pillars effectively out of the Circuit and do not interfere with the analysis of the selected fraction.

For this purpose, the invention is based on a method for chromatography Separation, in which a substance mixture is circulated one after the other and repeated is passed through a plurality of chromatographic separation columns, and at which Emix components, which are in front of a selected part of the mixture through the separation columns migrate, be removed from the circulation. According to the invention it is provided that after the selected part of the mixture has passed through a separation column, the mixture components, who run after this selected part, driven out of this separation column before the remaining mixture is returned to this separation column.

So there is no need to wait, as in the case of the known arrangement until the "heavy" ends of the chromator stem in normal gear through the Separation columns have migrated and are vented from the exit of the separation column into the open can. as soon as the components you are looking for have left the first separation column and the downstream Tren @ column separated from the first and immediately with a Carrier gas source is connected, is according to the invention by suitable measures made sure that those who remained in the first Treunsäule were no longer of interest "Heavy" components are driven out by suitable measures. This can e.g. done by gnawing, However, it is particularly advantageous if the mixture components are driven out of the separation column by flushing.

It is known per se, other components that are not of interest can be removed from the separation column relatively quickly by "back-flushing" it, i.e. that the direction of the carrier gas flow in the separation column is reversed. In the Components contained in the separation column then migrate backwards. Do this by hiking those components that have progressed furthest through the separation column were also the quickest way back to the entrance. The greater progress can be made yes, a consequence of a greater speed of migration. The components that are slower move, have also migrated less far into the separation column. The consequence of this is, since the various components after reversing the direction of flow appear again at the same time at the entrance of the separation column0 This is as if a Movie showing the progress of the components in the separation column, played backwards will. The time it takes for backwashing at the same gas velocity required is substantially equal to the time from the sample entering the column up to switching, as can be seen from the above without further notice. Bie is also roughly equal to the retention time of the components sought in one Separation column - By driving out the "heavy" components, the separation column becomes instantaneous ready again for a new separation within the framework of the cycle. ivian can In contrast to the known arrangement, all the separation columns for the Cycle exploit. It will diverge further in the further course of the cycle of the chromatogram repeats the "light" and the heavy ends of the chromatogram removed from the circuit. The former by venting into the atmosphere, the latter by expelling from a column. This means that the fractions are getting bigger and bigger Resolution is increasingly focused on a certain component.

The invention also relates to a device for performing the above Procedure.

An embodiment of the invention is shown in the figures and described below: Fig. 1 is a schematic illustration and shows an arrangement according to the invention of separating columns.

Fig. 2 is a schematic representation of a spool assembly, which perform the switching operations shown in Fig. 1 ge @ equips.

Fig. 3 shows another embodiment of the invention.

Fig. 4 shows a further embodiment of the invention and Fig. 5 shows a fourth embodiment of the invention.

FIG. 6 shows a valve arrangement for the arrangement according to FIG. 5.

Fig. 1 shows a novel sequence of compounds of chromatographic Separation columns progressing from circuit (a) to circuit (f). The course of action begin with Figure 1 (a) for purposes of illustration.

There are three separation columns 10, 20, 30 by means of suitable valve arrangements switched as shown. The end lol of the separation column lo is with a first Carrier gas source Pl connected. At S a sample can be injected. The end 102 of the separation column 10 is connected directly to the end 202 of the separation column 20, see above that components flow directly from the separation column lo into the separation column 20.

A detector 12 is arranged between the ends 102 and 2o2 to register the eluate of the separation column lo.

The end 201 of the separation column 20 is connected to the atmosphere via the outlet V 1 tied together. It can be seen that in the disorder of Figure 1 (a), columns 10 and 20 in Are connected in series, so that the carrier gas and the entrained sample one after the other walk through it. For the sake of simplicity it is assumed that the three pillars lower others are equal. However, that did not necessarily happen and should not be construed as limiting the invention.

During the time when the separation columns lo and 20 so for the passage the sample are switched, the separation column 30 is flushed by a carrier gas stream, which enters at the end 301 from a carrier gas source F2 and to an outlet V2 flows.

For the sake of clarity, it is assumed that a mixture separates should be, in which the particularly interesting components somewhere in the Middle range between the light and heavy components present in the sample falls. At the time when the components of interest enter the column ° o a occur, the lighter ends can be blown out of the outlet via outlet V1 Circuit has already been removed. At this point the pillars on the in The arrangement shown in Fig (b) is switched. The end 202 of the separation column po is now connected to the iräger5asquelle P 1. The end 201 of the column 20 is now with the End 301 of column 30 connected via detector 12. The end 302 of column 30 is in communication with the atmosphere via outlet V1. During the period where the separation columns 20 and 30 are connected in series in this way is the end 102 of the separation column 10 is connected to the carrier gas source P2 and the end 101 is stationary via the outlet V2 in connection with the atmosphere.

As has already been explained with reference to FIG. 1 (a), were the light ends of the sample had already been blown off via V1. They swear Ends that overflowed behind the components of interest were left in the separation column 10 withheld. It can now be seen (Fig. 1 (b)) that the separation column lo through pure Carrier gas is back flushed, thereby removing the heavy end components and the column is cleared for reuse. It goes without saying that the carrier gas pressure at P2 can be higher (or lower) than the pressure at P1.

The gas used for this purpose can also be used, although it is described above as the "carrier gas" is designated, possibly completely different from the carrier gas from PI if this should be necessary for the backwashing process.

Similarly, the gas from source P2 can be heated, to make it easier to drive out the heavy components. One further recognizes Fig. 1 (b) that the series connection cLer separating columns 20 and 30 again the blowing lighter ends allowed at Vi. If the components of interest are in the Separating column 30 enter, the separating columns to the in here. 1 (c) Arrangement to be regrouped. It can be seen from Fig. 1 (c) that pure carrier gas from PI enters the system at column end 301 and the sample comes out at end 302 and flushed into the end 102 of the separation column 10. From the end 101 comes the Rehearsal for 1, slaß Vi. Note here that the separation column 10 is a column that has been backwashed in the previous stage b, and the aaher for inclusion new sample material is ready. The separation column 20 is now from the Prooe containing flow system and is switched off by carrier gas, welc @ it from P2 flows to V2, backwashed.

If one follows the successive steps of Fig. I (a) ois Fig.1 (f) followed, it can be seen that this principle of the switching sequence continues. As the components of interest progress from column to column, will the lighter ends are blown off continuously and the heavier ends are constantly being blown off backwashed. Furthermore, the components of interest are constantly being put into one newly flushed column section.

Switching takes place from the arrangement shown in FIG. 1 (f) to the arrangement of Fig. 1 (a). This cycle can last as long as necessary is to resolve the components of interest.

YWn says that this arrangement in the end, at least as far as the components of interest is concerned with a separation column of unlimited length. This is achieved with a limited amount of separating material and a switchover clamp, which avoids an upper lobe of light and heavy ends as it normally does could be expected in a circulatory technique.

4. Fig. 2 is a suitable mechanical arrangement for implementation the one in Pig. 1 shown Scnaltvorgangs Geseigt. Iz Pig. 2 are the pillars 10, 20 and 30 of Fig. 1 connected via a twelve-way rotary valve 40, the one Has base body 41 and a rotor 43.

Six of the twelve connections of the slide 40 are labeled as it corresponds to the end of the separation column to which they are connected. The reference signs the connections are marked by a line () from the reference numbers of the corresponding Differentiated column ends. The remaining connections of the slide 4o are ready possible in accordance with the representation of FIG. Four of the rest Connections in the rotary valve are thus labeled VI, Y2, P1 and P2. To the the remaining two connections are the detector 12, and these are therefore with 121 and 122 denotes. A carrier gas source P feeds both Pl as shown also P2. Alltordek one can also find carrier gas on the reference side of the detector 12 make use of when a detector with a thermal conductivity bridge related will. The carrier gas from P flows through a valve 42 on its way to P1 Valve 42 is intended to represent an autosampler valve as described in the United States patent 2,757,541. Flows through the valve 42 via the lines 44 and 46 a constant stream of sample material. A writer 48 is attached to the detector 12 connected. The valve 4o can be operated either manually or automatically. If it is operated automatically, then it can be from the detector 12 or from a suitable timer can be controlled. The rotor 43 of the rotary valve 4o has six channels, which are arranged symmetrically to a diameter of the valve. Pointers 50, 52 indicate the positions of the slide rotor, which are indicated by digits t11f until "6" are marked 0 In the position shown in Fig. 2, the columns are connected so that as shown in Fig. 1 (a).

At the beginning of the cycle, the valve 42 is actuated, which is a sample introduces into the carrier gas stream which flows from P via line 13. The carrier gas and the metered volume of sample flows through line 15 and via the inlet P1 into the rotary valve 40. From the i) deer valve 40 they pass through one after the other Line 17, separation column 10, line 19, rotary valve 40, line 21, detector 12, Line 23, rotary valve 40, line 25, separating column 20, line 27 and rotary valve 4o to outlet V1.

The end 1o1 receives the sample, the ends 102 and 202 are over a Detector 12 connected together, and the end 201 is exposed to the atmosphere Connection as shown in Fig. 1a. While this arrangement is in effect, At the same time, carrier gas arrives from P via line 31, inlet P2, connection 301 Line 33 and flushes the separation column 30 back by moving from 301 to 302 and from since flows through a line 35 and the rotary valve 40 to outlet V2, Man now sees that a turn of the slide, by which the pointers 50, 52 are set to the marker digits "2", a circuit is obtained, as shown in Fig. 1 (b). The positions correspond in a similar way "3", "4", "5" and "o" correspond to the arrangements shown in Figs. 1 (c), 1 (d), 1 (e) and 1 (f) are shown.

Figures 3 and 4 each represent an anora with six separating columns u2, 64, 66, 72, 74, 76, with the ends of each separation column by adding the Numeral "1" or "3" are designated to the reference number of the respective column. Every The advantage of these designs is that they allow the simultaneous scoring of three Rehearsals allowed.

In both cases, the sample is injected into the column ends 524 and 7 @@. For the sake of simplicity, these samples are designated with Sa and sb in both figures. There are now four carrier gas sources Pl, P @, P3 and P4 provided in each Kusführungform. P1 and P3 represent those sources of truger gas that are used to generate the @sample components in the circuit to rinse through the separation columns. P2 and P4 are purge gas sources. The Sgül @@ s may or may not be the same as the carrier gas0 There are four cloths V1, V2, V3 and V4 presented. V1 and V3 represent the outlets in both figures for the easy ends, each from the second of the series connected Yrenn columns emerge.

V2 and V4 are in both cases the backwash outlets from @@ r column, tie is being prepared for renewed use. A comparison of Fig. 3 (a). - 3 (e) with Fig.1 (a) - 1 (e) shows that each group of three columns, namely 62, 64, o6 and 72, 74, 76 are similar to the correspondingly labeled parts of FIG. In 3 (f) are, however, the end 651 after the sample Sa has entered the separating coil 66 switched so that it is with the end 721 of the column 72 of the second Group is connected. The end of the column 761 becomes similarly quiet after entering the Sample Sb in the column 70 to the unde o21 of the column 62 switched. You can see that In this way, each of the samples Sa @ and Db on the second, from three separation columns existing circle is given. As a result, each sample goes through a complete one Cycle through each column group, going through each racing column twice in walks through opposite directions, and then comes into the second group of three separation columns in which the same cycle takes place 0 in Fig. 4 a similar arrangement is shown, but every test runs in this switching sequence Sat and whether close to each other through aile secas columns.

It can be seen that so far in -F-. 3 as well as in Fig. 2. the circulatory technology offers the same advantages as are described with reference to FIGS. While the components of interest are thus constantly circulating in a cycle Blow off the light ends and wash back the heavy ends so that it is constantly providing a new acid section for the advancing components.

It should be noted here that in the preceding description there is talk of blowing off the light ends and backwashing the heavy ends. This description assumes that the analysis is primarily based on the Separation of components from the smock area is interested. Yes, this representation is only chosen for the sake of simplicity.

The separation column sections can be switched over whenever it is desired according to the location of the particular components of interest. For example, the components that you want to separate are the easiest At the end of the mixture. In such a case, the easy ends are of course left out do not step outside. However, the presentation would be the same and the backwashing would continue to be done. However, pure carrier gas would be whatever you want, either blown off into the open or left in the circuit.

It would be similar if you wanted to separate the heaviest ends. then you would have to omit the backwash step but you would use the light ends as before let out in qie atmosphere. Then the clutter would work similarly to the arrangement according to German patent specification 1 079 352.

In Fig. 5, a modification of the invention is shown with two mrennsäulen works. In this embodiment, two separate carriers can swell for different pressures. One is used to carry carrier gas for to provide the normal chromatographic separation.

The other source of carrier gas is used previously with sample components loaded separation column by a short burst with carrier or purge gas with high Pressure to flush to prevent the fastest of the components you want overtake the slow components for the remainder of the cycle. The manner, how this technique is applied can be seen from B. 5 (a) to 5 (h). These Diagrams illustrate a switching sequence for separation using chromatographic Pillars ro and so.

In accordance with the notation described above the respective pillar ends are identified by the reference numbers of the pillar, to which the digits "1-" or "L2" are appended. To this embodiment To illustrate the invention, assume that a sample in that of the Carrier gas source P1 is injected into the column 8o2 flowing carrier gas. The interesting ones Components migrate through the column do, exit at the end 801 and enter the End 9o2 of column 9o.

At the same time, lighter ends can flow into the atmosphere at V1, while heavier components are retained in the separation column 80. If the interesting components have entered the separation column 9o, the columns can be switched to the arrangement of Fig. 5 (b).

In Fig. 5 (b) it can be seen that the separation column 80 with that previously described High pressure carrier or purge gas source P2 is in communication and via an outlet V2 is in connection with the atmosphere. The start flow caused by the elevated Backwashing pressure is created; it allows the time during which the arrangement of Fig. 5 (b) is to be kept brief. Remain during this backwash period the components of interest in the separation column 90. When the backwashing of the separation column 80 is completed, the columns are switched to the arrangement of Fig. 5 (c). The components of interest are now recirculated to the fresh ones rinsed separation column 80 given. Light ends come out at V1 and heavy ends stay in separation column 9o. A switchover then takes place again from this position in such a way that the separation column 9o can be backwashed with a pressure such as is shown in Fig. 5 (d). After this short backwash period, the columns will is switched to the position shown in Fig. 5 (e). One follows the representations further until 5 (h), it can be seen that this switching sequence continues. The interesting ones Components are transported in a cycle from one separation column to another, whereby the lighter components can each escape into the atmosphere and the heavy ends were backwashed at high pressure during short backwash periods and thus driven out of the separation column.

The components of interest are constantly on this journey give a freshly rinsed column section.

Starting from the arrangement according to FIG. 5 (h), the columns are again brought into the arrangement shown in Fig. 5 (a). The components of interest are transported through the columns in a continuous cycle for as long as it is necessary to effect your separation.

A device for performing the switching operations described above is shown in FIG. 6. In this embodiment, the columns So and 90 are used rotatably mounted.

The ends 801, 802, 9o1 and 902 are directly on the rotor 11o of the Rotary valve. The rotor 110 is rotatable by means of a compression spring 114 on a Stator member 112 held in position. @n the underside of the stator member 112 are four connections equiaxial to those arranged at the same distance from one another end of the columns So and 90 planned. In addition, a second valve 116 is in the circuit switched on to control the short rinsing process. The valve 115 has sec connections which are provided in a stator disk 117 and are arranged in such a way that that adjacent connections by means of rotatable arcuate connecting channels 118, 120, 122 can be panaen with one another in the rotor disk 119. This valve can be designed similarly to the cias valve in the already mentioned USA patent 2 757 541 is described and illustrated. However, valve 116 does not contain a sampling loop.

P2 is a relatively high pressure purging gas source that is connected to aem connected to @ chluß 124. In the position shown, purge gas is passed through the Leave connection'126 to outlet V2. In the meantime, the carrier gas is released normal pressure from P1 into the port 128 and continues to flow from the port 1Do to the end do2 of the column do. Samples 5 be introduced. The carrier gas and the entrained gas pass from the end of the column 8o1 i? rooe into port 132 and through port 134 into column end 902. From the column end 901 allows the carrier gas and the separated components to the outlet V1.

It can be seen that the valve positions shown in Fig. J control the switching of Fig. 5 (a). At the appropriate moment the gas valve is opened as described 116 actuated so that it connects terminal 32 with 124, 120 with 130 and 128 with 134. -aan sees that the arrangement of Fig. 5 (b) is achieved with this switch position. If a sufficient period of time has elapsed, the valve 116 will return to its returned to its original position, and at the same time the rotor 110 is in the The direction of the arrows is twisted so that each separating column after the neighboring one Connections aes stator 112 is aligned. This creates the one shown in Figure 5 (c) State of flow. By continuing the relative movements of valves 116 and 1, Any of the schemes illustrated in Figure 5 can be achieved.

A number of modifications of the invention are possible, if for example also horns with two, three and six columns have been described similar techniques can be used using other multiples. if a double sample injection is also described in connection with FIGS simple injection could or could be used a larger number of injections take place.

The use of a plurality of injections, in which the various Samples following one another in the circuit have the advantage that one can switch can use a single program switchgear. Of course, such a system would a relatively precise adjustment of the separation columns with regard to the flow resistance make necessary. Changes in resistance should be compensated for as far as possible are supported by pillars with alternating high and low resistance. because one "Grafting" task (i.e. fairly long, rectangular sample application) is used, then minor changes in the value of the column would become an occasional one Distortion of the plug ends. But this effect would not be cumulative since the total transit time of each sample would be the same. The term "K '" relates focus on the relationship. k '= k. Cowardly.

Fgas and is on page X at Keulemans "Gas Chromatographie" Verlag Chemistry edition defined in 1939.

The term "soil" or "theoretical soil" is used in gas chromatography Commonly used to define the performance of a column. A complete Explanation of this term is given in the book by Keulemans cited above. For the purposes presented here, it can be said that the separability of a column The greater the number of "bottoms", the greater. If from every separation column a group contains nl soils, and iff the sample is circulated n2 times through the Columns, the effective number of ponds is n1 n2. If a jagged If the sample is spread over n1 n2 soils, then the myriad of distinguishable components within a column of n1 soils n1 if the user is interested in isolating a single component, he can make n2 = n1.

Claims (12)

Claims 1. A method for chromatographic separation in which a substance mixture in the cycle successively and repeatedly through a A plurality of chromatographic separation columns is passed, and in which mixture components, which migrate through the separation columns before a selected part of the mixture be removed from the circuit, characterized in that after passage of the selected Part of the mixture through a separation column, the mixture components, which are behind run towards this selected part, be expelled from this column of blood before the remainder of the mixture is poured onto this rotary column again. 2. The method according to claim 1, as @ urch @ characterized as £ the expulsion the mixture components are carried out from the separation column by backwashing 3. Procedure According to claim 1 or 2, characterized in that for the separation of a selected one Part of a sample, a mixture of sample and carrier gas through a first separation column @ is directed and thereby fractions of the sample are separated from each other that one or one of the separated fractions on a second chromatographic separation column be directed, whereby the previously appeared fractions removed from the @reilauf be, and one of the separation columns during a given period of time ni is purged with pure carrier gas, whereby the separation column for a follow on Cycle cleared and certain selected fractions of the sample out of circulation be removed while at the same time passing through the other fractions of the sample hike the second or one of the other separation columns. 4. The method according to claim 3, characterized in that each the carrier gas is vented at the downstream end of a separation column and to the At the same time, another separation column is freed of sample components by backwashing will. 5. The method according to claim 4, characterized in that ate the selected Sample fraction is cyclically passed through two separation columns, of which alternately one is backwashed. 0. The method according to claim 5, characterized in that the period of time the backwash Rurz compared to the breakthrough time of the selected sample fraction through the separation column. 7. The method according to ns3ruch 4, characterized by the use of at least Grei separation columns. 8. The method according to claim 7, aadurcn geken @@ eichnet, aaw the simultaneous Blowing off and backwashing, at least in part, takes place during the time that the selected fraction is in a third separation column. 9. The method according to claim 4, characterized by the use a multiple of three columns. 10. The method according to claim 9, characterized in that aass in the Carrier gas stream several samples are introduced. 11. Apparatus for performing the method according to claim 1, with a A plurality of chromatographic separation columns, means to convert a mixture of substances in the Cycle successively and repeatedly burcn to lead this Frennsäule, and means, around mixture components, aie before a selected part of the mixture through the separation columns migrate, to be removed from the cycle, characterized in that means are provided after passage of the selected part of the mixture through a separation column the mixture components, which run after this selected part, from this Drive off the Frenn column before putting the remaining mixture back on this column is given. 12. The apparatus according to claim 11, characterized in that the Propellant of means for reversing the direction of flow in the racing column are formed.