SEMI-SOLID SAMPLE

The present invention relates to a method for ex- traction of a solid or semi-solid sample, and to an extraction device for carrying said method into effect.

The preparation of extracts from substances, liquid as well as solid, for various examination and control purposes is conventional laboratory routine, for example in order to determine the peroxide content, i.e. the degree of rancidity, of a wheat sample.

The extraction is largely carried out manually by placing a sample in a test tube which is then filled with a specific amount of a solvent, such as ether, chloroform or alcohol. Then the sample is mixed with the solvent by shaking or stirring. In these cases, the resulting solu¬ tion must finally be filtered since any particles re¬ maining in the solution may interfere with the examination and adversely affect the examination result. A number of publications, such as EP-A3-0,072,201, US-A-3,932,277, US-A-3,799,342 and US-A-4,035,294, de¬ scribe how a sample is washed or extracted under cen- trifugation.

Several of these publications disclose extraction vessels which, however, are designed to give maximum effect during centrifugation. The centrifugation itself entails several other problems, especially during extrac¬ tion of a solid or semi-solid sample.

In manual extraction, there is a considerable risk that part of the solvent evaporates, and this affects not only the extract and, consequently, the examination re¬ sult, but also the job environment. Frequently, the sol¬ vents employed are highly volatile and poisonous or numbing. Consequently, a far-reaching automation of the extraction process is desirable.

The above-mentioned publications are illustrative of the prior art technique directed to the centrifugation of extraction vessels for particle washing in a first solu¬ tion by means of a solvent, while for example US-A- 3,752,651 discloses an apparatus for rotating test tubes about the longitudinal axis of each test tube.

Although this apparatus makes it possible to dispense with the manual shaking or stirring, it does not eliminate the difficulties encountered in the extraction of solid or semi-solid samples.

It therefore is an object of the present invention to provide a method for extraction of a solid or semi-solid sample without heat supply, the sample being repeatedly flushed with the same amount of solvent, i.e. for sequen- tial extraction of the sample.

A furhter object of this invention is to provide an apparatus with at least one sealed extraction unit for extraction of a sample under special conditions, for example in a dark room and/or a refrigerating chamber, in a special atmosphere, such as a shielding gas atmosphere, or when using a solvent injurious to health.

A third object of this invention is to provide an apparatus for rotating the extraction unit in such a manner that a given amount of a solvent, after passing through the sample, is collected and again caused to flow through or over the sample.

A fourth object of this invention is to provide an apparatus in which the solvent is moved relative to the sample without supply of thermal energy. These and other objects are achieved by a method for extraction of a solid or semi-solid sample, said method being characterised by causing an amount of a solvent to flow through an extraction sleeve disposed within an extraction unit and accommodating the sample; collecting said amount of solvent at one end of the extraction unit; and rotating the extraction unit to cause the collected amount of solvent first to flow past the extraction sleeve

and then again flow through the extraction sleeve containing the sample, whereby sequential extraction of the sample is obtained.

To achieve the above objects and to carry the method into effect, the present invention provides an extraction device for extraction of a solid or semi-solid sample, said device being characterised by at least one extraction unit comprising an extraction sleeve for accommodation of the sample, a hollow extraction head, the lower part of which has an opening on which the extraction sleeve is mountable, an extraction tube having an open end for accommodating a solvent, in which extraction tube the extraction head is partially insertable for fixing and/or closing the extraction tube with the opening of the ex- traction head positioned underneath the fixing or closing area, and a connector between the extraction tube and the extraction head for one-way transfer of the solvent from the extraction tube to the extraction head from which the solvent is recycled to the extraction tube via the extrac- tion sleeve.

The extraction device is further characterised by a holder which is rotatably mounted in a frame about a hori¬ zontal axis and in which one or more extraction units are removably attached, and by drive means for rotating the holder about the horizontal axis.

The attached drawings illustrate an embodiment of the device according to the invention for extraction of a sol¬ id or semi-solid sample, said embodiment being described in detail hereinafter. Fig. 1 shows an extraction unit according to the in¬ vention.

Fig. 2 illustrates schematically a device for extrac¬ tion of a solid or semi-solid sample with a plurality of the extraction units shown in Fig. 1. Fig 1 shows an extraction unit 10 which, in this case, comprises an elongate extraction tube 12. The extraction tube contains a solvent 14 with an upper

surface 16. The extraction tube 12 has an open end 18 in which an extraction head 20 is partially insertable.

The extraction head 20 is hollow and has, in its lower part 22, an opening (not shown) to which an ex- traction sleeve 24 is removably attached.

The extraction sleeve 24 is made of a permeable material suitable for extraction of a solid or semi-solid sample. The material is to carry the sample and simul¬ taneously to allow the solvent and parts of the sample dissolved therein to pass.

Like the extraction tube 12, the extraction head 20 is preferably circular, the lower part 22 of the extrac¬ tion head 20 having a diameter less than the inner diameter of the extraction tube 12. The shape of the extraction tube 12 is such, for example a conical shape of the end having the opening, that the partially inserted extraction head 20 is fixed and/or the extraction tube is closed, the opening of the extraction head 20 being positioned underneath the fixing/closing area.

A preferred embodiment of the extraction head 20 is formed, between the fixing/closing area and the opening of the extraction head, with two essentially diametrically opposed connecting passages 26, 28 each extending through the wall of the extraction head 20 and communicating the interior of the extraction tube 12 with the interior of the extraction head 20.

In another embodiment (not shown) of the present in¬ vention, the connecting passages 26, 28 have been replaced by one-way valves formed in the wall of the extraction head 20 and communicating the interior of the extraction tube 12 with the interior of the extraction head 20, to permit liquid or gas flow in but one direction.

One passage 26 is in the form of a tube extending to the upper part 27 of the extraction head 20, while the other passage 28 is a tube extending but a short distance up into the extraction head 20. The passage 26 serves to

transfer liquid, and the other passage 28 is a pressure equalising passage.

Fig. 2 shows a device for automatic extraction of a solid or semi-solid sample, comprising a holder 30 rotat- ably mounted in a frame 32 for rotation about a horizontal shaft 34. In Fig. 2, six elongate extraction units 10 according to Fig. 1 are detachably mounted in the holder 30 in such a manner that the longitudinal axis of each extraction unit 10 is perpendicular to the horizontal shaft 34. In this embodiment of the invention, the de¬ tachable mounting is achieved by means of a cross beam 37 provided with clamps.36a and 36b. A drive means in the form of a motor (not shown) and a transmission 40 is rendered operative by a control unit 38 for rotation of the holder 30 and thus the extraction units 10.

In order to carry the method of the invention into effect, the extraction device is prepared as follows. The sample, for example wheat to be extracted for determina¬ tion of its peroxide content, is placed in the detached extraction sleeve 24 of permeable material of the above- mentioned type. The extraction sleeve 24 is closed after application of the sample by means of a plug which also is permeable, for example a wad of cotton wool, whereupon the closed extraction sleeve 24 containing the sample is placed over the opening in the lower part 22 of the extraction head 20.

Before the extraction head 20 with the extraction sleeve 24 is inserted in the extraction tube 12, the latter is supplied with a specific amount of a solvent 14, for example alcohol or ether. This operation is preferably carried out in a fume cupboard in which also the extrac¬ tion head 20 containing the sample and the extraction tube 12 containing the solvent 14 can be assembled. The extrac¬ tion sleeve 24 is of such a shape and size that it can be attached, for example by means of a clamping ring, to the lower part 22 of the extraction head 20, and that the ex¬ traction sleeve, when held vertically, and with the ex-

traction head 20 and the extraction tube 12 in the as¬ sembled state, is located above the surface 16 of the solvent.

In this manner, a closed extraction unit is obtained, the interior of which does not communicate with the ambient atmosphere, but which may be provided with a pressure equalising valve for pressure equalisation in an initial stage before the extraction proper.

If the solvent employed is nonvolatile at working temperature, the extraction tube may, of course, be pre¬ pared first.

A number of extraction units 10 are assembled in ac¬ cordance with the above description and clamped in the vertical initial position in the holder 30 shown in Fig. 2 with such an orientation that the solvent 14 upon rotation of the extraction unit first flows towards and through the liquid transfer passage 26. In the embodiment illustrated, the clamping function is achieved by means of the cross¬ beam 37 and the clamps 36a, 36b. The following description of the course of events when the holder 30 and the extraction units 10 are operated (in this instance rotated) about the horizontal shaft 34, is applicable to all of the extraction units 10 clamped in the holder 30, and therefore only the operation of one extraction unit 10 is described.

After the desired number of flushings (in this in¬ stance the number of revolutions) have been fed into the control unit 38, and after pushing the start button, the control unit 38 activates the motor (not shown) which, via the transmission 40, initiates the rotation of the holder 30 and thus of the extraction unit 10, the direction of rotation being indicated in Fig. 1 by the arrows A.

At an angle of about 90° to the vertical initial position of the extraction tube 12, the solvent 14 flows along the inner wall of the extraction tube 12 past the extraction sleeve 24 containing the sample to the liquid transfer passage 26 to be collected in the hollow extrac-

tion head 20. At an angle of rotation of about 180°, all solvent 14 has collected in the hollow extraction head 20 which at this time is in a position directly below the initial position. Any gas, such as air, initially present in the extraction tube 20 is displaced by the solvent 14 entering the extraction head 20 and flows through the pressure equalising passage 28 past the extraction sleeve 24 containing the sample to the extraction tube 12.

Upon continued rotation of the extraction unit 12 in the direction of the arrows A, the solvent flows along the inner wall of the hollow extraction head 20. After rota¬ tion through about 280", the opening of the passages 26, 28 is above the level of the solvent. Since the solvent cannot flow back into the extraction tube 12 via any of the passages 26, 28, it is forced, at an angle of rotation of about 270° relative to the initial position of the ex¬ traction unit 10, to flow into the lower part 22 of the extraction head 20 through the opening herein and from there through the extraction sleeve 24 containing the sample.

Rotation is continued until the holder 30 and thus the extraction unit 10 have made a complete revolution, i.e. until they again assume their initial position. In this position, the control unit 38 interrupts the rotation of the holder 30 and thus of the extraction units 10 so that the solvent 14 can flow, in the right and proper manner, through the permeable extraction sleeve 24 containing the sample and recollect on the bottom of the . extraction tube 12. It has been found that optimal results are obtained with a time of revolution of about one minute, and that a waiting time of about four minutes in the initial position after a complete revolution gives the solvent ample time to interact with the sample and collect on the bottom of the extraction tube 12. However, these times may vary depending on the sample type, the solvent type etc.

At the end of the waiting time, and after the number of revolutions has been reduced in a revolution counter of the control unit 38, the motor is reactivated if the num¬ ber of remaining revolutions is higher than zero, and a new revolution is initiated, whereby sequential extraction of the sample is obtained.

The invention thus proposes an extraction device for extraction of a. solid or semi-solid sample, said device being capable, after a minimum of manual preparation, of automatically performing sequential extraction of the sample. The extraction is carried out in a closed system, which means that no loss of solvent occurs. The extraction device according to the invention makes it possible to ex¬ tract the sample under special conditions, for example in a dark room and/or refrigerating or heating room, and in a shielding gas atmosphere, to protect substances suscep¬ tible to oxidation. The device can be operated also in the absence of the laboratory staff.

It will be appreciated that anyone skilled in the art will find it obvious to change or modify both the method and the device according to the invention. Thus, it is not essential to the function of the present invention that the device is rotated, if for example a pendulum movement produces the same technical effect. Nor is the extraction unit limited to any specific construction as long as it gives the above-mentioned desired effect. In view hereof, the appended claims must be interpreted to comprise all changes and modifications that fall within the scope of the basic idea of this invention.