The present invention relates to a method for extraction of extractable components, such as dissolved substances, colloidal and/or suspended particles, in liquids. The invention relates especially to an on-line flow extraction method including the following consecutive steps:

- providing a flow of a first liquid including the extractable components,

- introducing into the flow of the first liquid a second liquid mainly immiscible with the first liquid, for extracting at least a portion of said extractable components from the first liquid into the second liquid, and

- separating the second liquid, including at least a portion of the extractable components, from the combined flow of said first and said second liquid.

The present invention also relates to an apparatus for on¬ line flow extraction of extractable components, such as dissolved substances, colloidal and/or suspended particles, in a liquid. Such apparatus including:

- a first tube or channel having a flow of a first liquid there through, the first liquid including the extractable components, and

- an other tube or a nozzle connected to the first tube, for introducing a second liquid mainly immiscible with the first liquid into the first tube.

A central need in analytical chemistry is to be able to work up and concentrate different samples of substances in order to be able to perform chemical analysis. Secondary or interfering matrix components have to be removed, whereas components, which are to be analyzed, often are extracted

into a medium, which is compatible with the subsequent analysis method. This step usually also leads to concentration of the components.

It is e.g. possible to extract dissolved hydrophobic substances present in a water-based sample, such as industrial or municipal waste water, from the water into different organic solvents, e.g. hexane, by extracting the water-based sample with a small amount of the solvent. Thereby a concentrate of hydrophobic substances in an almost water-free hexane phase is obtained. Immiscibility of liquids is necessary for conducting the liquid/liquid extraction, as the liquids have to be separated into two different phases after the extraction.

Liquid/liquid extraction techniques commonly used today include manual/mechanical shaking or mixing of the sample with extraction medium or solvent. However, also flow extraction systems with continuous liquid/liquid extraction are known. These systems include a continuous and controllable introduction of solvent into a stream of sample to be analyzed.

In these Flow Injection Analysis (FIA) systems discrete segments of the sample and the extraction medium are formed. A gradual extraction occurs in an extraction coil or tube, the time needed to obtain an equilibrium depending on the extraction kinetics.

The FIA systems usually employ a tube with a T-connection for introducing extraction medium into the flow of sample. This system has e.g. been used for analyzing waste water or drugs present in water-based solutions. Coaxially arranged tubes may be used besides the aforementioned tube with a T- connection.

A problem arises, however, when colloidal substances, such as fat droplets in water, or very fine particles suspended in water, are to be extracted. Such colloidal or very finely dispersed substances may e.g. have a negative surface charge which stabilizes the colloidal state. Frequently also other mechanisms, such as steric stabilization through formation of a protective polymer layer on the finely dispersed droplets, further stabilizes the colloidal or suspended state. This situation has been noticed to occur e.g. when fat/resin droplets formed in paper mill process waters are covered by a thin layer of hemicellulose.

As attempts have been made to perform a continuous extraction of aforementioned colloidal fat/resin drops into an organic solvent it has been noticed that the earlier mentioned flow injection analysis, FIA, gives an extremely poor extraction yield. This is believed to be a result of minimal organic solvent / colloidal particle contact over interfacial boundaries between organic solvent and sample segments. Repulsive electrostatic forces being formed in the phase boundary layers prevent the colloidal substances from coming into sufficient contact with the organic solvent phase. Almost no extraction takes place in spite of a relatively good contact between the two main phases, the organic phase and the water phase. The situation is different for substances dissolved in water. A pure two phase system leads rather rapidly to an extraction equilibrium. The fat/resin drops, however, have a very poor solubility in water.

It is known that the aforementioned problem can be solved by vigorous mixing of the liquids, e.g. by manual shaking.

The extraction medium, the solvent, is thereby finely dispersed and a forced contact between colloidal particles

and extraction medium is accomplished.

The applicability of the manual shaking method has been shown in laboratory tests extracting colloidal substances from paper industry process waters. A vigorous shaking of such a water sample with methyl-tertiary-butylether for a period of ca. 2 minutes, gave a satisfactory extraction of the colloidal substances. Manual liquid/liquid extraction procedures are, however, usually time and solvent consuming. It is, also, difficult to apply this mechanical shaking method in continuous or on-line analyzing systems, especially when working with small dimensional samples.

Reducing system and sample dimensions has become a more and more important aspect in analytical applications, e.g. in order to minimize consumption of chemicals, for cost and environmental reasons. Especially in situations where only minimal amounts of a sample is available, as in an number of medical related analysis, it is essential to be able to miniaturize the analysis system.

It is an object of the present invention to provide an improved method and apparatus for on-line flow extraction particularly of colloidal and/or suspended substances in liquids. It is thus an object of the present invention to provide a method which makes possible an efficient and fast on-line flow extraction of dissolved, as well as colloidal particles, suspended particles or extractable compounds adsorbed to particulate matter.

It is further an object of the present invention to provide an improved on-line flow extraction method and apparatus applicable in chemical analysis, as well as, in producing substances from extractable matrices.

It is still further an object of the present invention to provide an on-line flow extraction system needing only minimal amounts of sample and extraction solvent.

According to the present invention the above mentioned objects are achieved by methods and apparatus characterized by the features stated in the appended claims.

It has now surprisingly been found that an on-line flow extraction can be efficiently performed also of colloidal or suspended particles in a liquid by injecting the solvent or extraction medium as a high velocity jet stream into the flow of sample in an extraction tube. In order to accomplish this high velocity jet stream a narrow inlet passage or nozzle between the extraction tube and solvent inlet combined with a high pressure at the solvent inlet, usually in the range of 25 - 400 bar, is needed.

It is essential that the jet stream formed has a high enough kinetic energy for the solvent to immediately disintegrate into fine droplets having an impact on colloidal or suspended particles in the sample flow. The solvent is preferably disintegrated into fine droplets having a diameter of about 0.1 - 10 μm. The kinetic energy of the jet formed should preferably be high enough for the jet to be able to penetrate the flow of sample and hit the opposite inner side wall of the extraction tube. Preferably the jet reaching the other side wall should still have a kinetic energy high enough to be at least partly reflected from that other side wall back into the flow of sample.

The term "extraction tube" is here used for a wide variety of tubes or channels in which extraction medium, such as organic solvent, is mixed into the flow of sample. The extraction tube may be a tube or an extraction channel

formed between two plates or some other suitable construction.

The term "narrow inlet passage" is here used for a wide variety of nozzles or small openings, such as capillary nozzles, narrow bore capillaries or capillaries with a narrow bore insert, simple narrow bores, circular or non- circular in shape, which may be used to inject solvent into the extraction tube.

The term "colloidal or suspended particles" refers here to liquid, as well as, solid particles in a more or less stable colloidal or suspended form.

In an extraction process according to the present invention, the flow of sample liquid, including dissolved, colloidal and/or suspended material, is continuously or intermittently pumped or conveyed by suction through an extraction tube or sample tube. A second liquid, the extraction medium or solvent is introduced into the extraction tube through a solvent inlet tube. The second liquid is injected at high pressure providing a high velocity via one or several narrow inlet passages.

A solvent inlet tube may be directly or indirectly connected to the extraction tube. The outlet end of a solvent inlet tube, which is directly connected to an opening in the side wall of an extraction tube, may itself be small enough to provide the narrow inlet passage or nozzle needed for injecting the solvent. Alternatively a narrow bore capillary insert may be placed in the outlet end of an inlet tube of ordinary dimensions to provide the narrow inlet passage. In still another alternative application, where an inlet tube of ordinary dimensions is directly connected to the extraction tube, only a very

small opening/bore may be made in the side wall of the extraction tube for providing the inlet passage needed between the tubes.

Also in applications, where the solvent inlet tube is indirectly connected to the extraction tube, a narrow bore or other suitable narrow opening may be made in the side wall of the extraction tube, to provide for the narrow inlet passage needed for injecting solvent.

In the extraction process preferably, rather narrow extraction tubes are used. The extraction tube, i.e. the sample tube, may have an inner diameter of about 0.1 - 2 mm. The narrow inlet passages used to inject solvent into the extraction tube may be constructed, as mentioned earlier, in several different ways but should preferably, when circular, have an inner diameter of about 5 - 20 μm. It is further advantageous that the narrow inlet passages are made as short as possible, in order to prevent the need for excessive pressures for injecting the solvent at the inlet. Only very short capillary nozzles or short narrow bore inserts should be used in order not to increase pressure drop unduly. Narrow inlet passages made directly in the side wall of the extraction tube may have a funnel like shape converging toward the extraction tube.

By injecting the extraction medium at a high flow velocity into the sample flow, the extraction medium is dispersed into very small micro droplets, which are vigorously mixed with the flow of samples leading to an efficient extraction process. The micro drops formed have a high kinetic energy, 1/2 mv ² , analog e.g. to the action of a water jet of a high pressure cleaning gun, used for cleaning solid surfaces. The high kinetic energy leads to forced collisions and efficient contact between the micro drops of solvent and

colloidal or other particles present in the sample flow.

The pressure needed in order to obtain the objectives of the present invention, may vary within a wide range depending upon specific sample flow, the specific extraction medium and the apparatus used. The man skilled in the art will, however, find no difficulties in establishing the pressure needed to disperse the extraction medium in a sufficient manner.

The high pressure injection of extraction medium results in an effective and almost momentary extraction of colloidal and suspended substances. An equilibrium is, however, also simultaneously achieved between substances dissolved in the flow of samples and the extraction medium. Eventually a coalescence of micro drops into larger drops and segments of extraction medium will occur downstream of the injection point in the extraction tube. The extraction medium segments can be separated in a phase separator as a continuous flow from the flow of sample. Different types of continuous phase separators, described in literature, may be used for separation of the two phases. A pressure optimized porous PTFE membrane separator for instance allows only organic solvent to pass the pores in the membrane, whereas a water phase is not able to wet the membrane. In a settler, different phases are simply separated due to their difference in densities.

In the extraction apparatus two or more narrow inlet passages may be arranged in series or parallel. In an apparatus, having several narrow inlet passages in series, a repeated extraction process takes place, which will increase the efficiency of the extraction process and further improve the yield of the extraction. Of course, different extraction mediums, solvents, may be introduced

through the different inlet passages, if different components are to be extracted in successive steps. Introducing solvent through several parallel inlet passages is useful when larger sample flows are to be analyzed, as it increases the capacity of the extraction process.

The narrow inlet passage(s), e.g. the capillary nozzles, are preferably arranged to direct the inlet flow of extraction medium, e.g. an organic solvent, perpendicularly into the sample flow. When the extraction medium is injected perpendicularly dispersion into fine droplets is additionally enhanced due to the strong impact of the jet of micro drops onto the opposite wall of the extraction tube.

The new method and apparatus may be used to extract components that are permanently or only momentarily present in a liquid in a dissolved, colloidal or suspended state. A suspension of water and a solid or liquid medium, including the extractable component, may e.g. in some applications be prepared by mixing solid particles into water only immediately before injecting the extraction medium into the water. The suspension thus prepared may only be stable for a time period long enough for the extraction to take place.

The new method and apparatus may e.g. be used not only for analysis of components, but also for extraction of components from colloidal or suspended particles, in order to produce a product including these components.

The new method and apparatus may further be applied for separating solid components from the surface of solid particles suspended in a liquid. The jet of extraction medium having a very high velocity, i.e. high kinetic

energy, may be used to "peel" off certain layers of solid material from solid particles suspended in e.g. water.

The invention is in the following discussed in more detail with reference to the enclosed drawings, in which

FIG. 1 shows a schematic cross sectional view of a T- connection tube used in a conventional flow extraction system for injecting extraction medium into a flow of sample to be analyzed,

FIG.2 shows a schematic cross sectional view of a T- connection tube used for injecting extraction medium in accordance with the present invention,

FIG. 3 shows a schematic cross sectional view of another apparatus, according to the present invention,

FIG. 4 shows a cross section of the apparatus in FIG 3 along line AA' ,

FIG. 5 shows a schematic cross sectional view of still another apparatus according to the present invention,

FIG. 6 shows an enlarged view of the encircled portion in FIG. 5,

FIG. 7 shows a schematic cross sectional view of a further apparatus according to the present invention,

FIG. 8 shows a cross section of the apparatus shown in FIG. 7 along line BB' and

FIG. 9 shows a top view of the apparatus in FIG.7.

FIG. 1 shows a schematic cross sectional view of a T- connection tube 10 used in a conventional flow extraction system (FIA) for injecting extraction medium into a flow of sample, which is to be analyzed. The T-connection tube includes a main tube 12 and a branch tube 14. A flow of sample 16 to be analyzed is pumped or suctioned through the

main tube 12 in the direction shown by the arrow. Extraction medium 18 is introduced into the main tube through the branch tube 14 connected to an opening 20 in the side wall 22 of the main tube 12.

Extraction medium, which is immiscible with the sample to be analyzed or extracted, flows out from the branch tube 14 into the main tube 12 forming large discrete segments 24. The extraction medium, e.g. a hydrocarbon, and the sample, e.g. a water based solution, form consecutive segments flowing downstream towards a phase separator not shown. Solvent-soluble dissolved substances in the sample are extracted at an acceptable speed into the extraction medium.

FIG. 2 shows a T-connection tube 10 used as an extraction apparatus, in accordance with the present invention. The apparatus includes a main tube 12, i.e. the extraction tube, having a continuous flow of sample therein, and a branch tube or capillary 14, i.e. the solvent inlet tube, connected directly and perpendicularly to the side wall 22 of the main tube 12. A very small inlet opening 26, i.e. the narrow inlet passage, is formed in the side wall 22 for connecting the branch tube 14 with the main tube 12.

A high pressure pump, not shown, is connected to the branch tube 14 for forcing the extraction medium at a high velocity through the small inlet opening 26, whereby a jet stream of high velocity extraction medium is obtained in the main tube 12. The direction of the jet stream is perpendicular to the flow direction of liquid in the main tube. The jet of extraction medium is immediately dispersed in a large number of micro droplets 28 and is thereby very well mixed with the sample flow. An efficient and almost momentary extraction takes place. Downstream of the

injection point 30 micro droplets 28 coalescence into larger droplets 28' and further downstream into still larger segments 28' ' . The large segments 28" are separated from the flow of sample in a phase separator not shown.

The main tube 12 and the branch tube 14 may be made of metal, glass, silica or some other suitable material. In FIG. 2 one branch tube is connected perpendicular to the side wall of the main tube. In other applications of the present invention it may be suitable to connect several branch tubes in series or use other types of branch connections, such as Y-connections or W-connections known per se.

FIG. 3 and FIG. 4 show another variation of the T- connection tube. In this construction the section 32 of the main tube 12 including a harrow inlet opening 34 is coaxially surrounded by another tube 36 having a slightly larger diameter. The outer tube 36 is welded gas tight around to the main tube 12 to form an annular space 38 between the tubes 12 and 36.

The annular space 38 is pressurized with extraction medium through a branch tube 14, which is connected to the gas space through an opening 40 in the side wall 42 of the outer tube 38. The tube 14 is thereby indirectly connected to the main tube 12. The opening 40 between the tube 14 and the annular space 38 may be of ordinary dimensions. The inlet opening 34, formed in the side wall of the main tube and connecting the annular space 38 with the inside of the main tube 12, is made as a very small diameter bore, e.g. having a diameter of about 5 - 10 μm.

A high pressure pump, not shown, is connected to the branch tube and used to force the extraction medium to flow

through the narrow inlet opening 34 into the main tube 12 at a flow velocity of e.g. 0.5 - 1 ml/min. The sample is pumped through the main tube 12 with a flow velocity of e.g. 2 ml/min.

The construction shown in FIG. 3 and 4 utilizes as a test or main tube 12 a thin-walled steel tube, having a 0,1 mm material thickness. The small diameter bore or inlet opening 34 may be drilled in the thin-walled steel tube 12 with a laser, whereby the bore forms a nozzle with a very small length.

Fig. 5 and 6 show another extraction apparatus according to the present invention. A thin-walled glass or fused silica capillary tube 14, having an inner diameter of about 150 - 250 μm, is connected to a main glass tube 12, having an inner diameter of about 1 mm. The capillary tube 14 is glued with silicone glue, or any other solvent resistant glue, to the glass tube 12.

In order to decrease the cross sectional area of the inlet opening between the glass tube and the silica capillary tube 14 a short, e.g. 500 μm, inner piece of glass or fused silica capillary 46 is inserted into the end 48 of the capillary tube 14 before it is connected to the main tube. The outer diameter of the inserted inner piece of capillary 46 corresponds to the inner diameter of the outer capillary tube 14. The inner piece of capillary is glued with a polyimide glue 50 or other solvent resistant glue to the end 48 of the outer capillary tube 14. The inner diameter 44 of the separately inserted inner piece 46, forming the narrow inlet passage between the solvent inlet tube 14 and the extraction tube 12, may be very small e.g. about 5 - 10 μm.

The combined capillary construction 14 and 46 is glued with a silicone glue 52 to an opening 44 prebored in the glass tube 12. The end 48 of the combined capillary is connected to inject solvent perpendicularly to the direction of flow in the glass tube 12.

In use, the silica tube 14 is pressurized with extraction medium, with e.g. a high performance liquid chromatography HPLC pump, to a pressure preferably between 50 - 400 bar, while simultaneously conveying a flow of the sample through the glass tube 12 with a low pressure pump, 0.5 - 1 bar, such as a peristaltic pump.

In FIG. 7 to FIG. 9 a further construction of an extraction apparatus according to the present invention is shown. This construction provides a very small/miniature flow extraction apparatus applicable e.g. in clinical biochemistry or for determination of drugs in pharmaceutical preparations.

The extraction tube, i.e. the main channel 54, is made between two plates 56 and 58 made of silicon. The channel m=.y be made extremely small suitable for very small sample flows. The main channel 54, which in this application has a non-circular cross-section is formed between the plates 56 and 58 by etching a channel onto the surface of plate 58. Further a small narrow inlet opening 60 is formed in the channel 54 by etching an opening, e.g. a square hole or a slot, in plate 56. By etching in onocrystalline silicon it is possible to form extremely small channels and openings, which have a high accuracy. The silicon plates 56 and 58 may be connected to each other by gluing, anodic bonding, heating or other suitable methods known per se.

A cover plate 62 is arranged to cover the inlet opening 60

on the external side of plate 56. A gas tight space 64 is thereby formed between the cover plate 62 and plate 56. A capillary tube 14 (not shown) is connected to an opening 66 in the cover plate for introducing extraction medium into the space 64.

In use the gas tight space 64 is pressurized by extraction medium, which is introduced with a high pressure pump through opening 66. High pressure extraction medium is forced to flow through opening 60 from space 64 into the flow of sample in the channel 54.

If several inlet openings are made in plate 56 and/or plate 58 the combined plates may be enclosed in a gas tight outer tube or chamber, instead of using a cover plate 62 to form the gas tight space 64. The gas tight outer tube or chamber may then be pressurized with the extraction liquid.

The main advantages achieved with a silicon construction are high accuracy, as well as, an extremely narrow solvent inlet passage. The inlet pressure needed to force a high velocity solvent jet through the narrow inlet passage is lower than in other cases due to the lower pressure drop in the extremely short passage. One further advantage achieved is the possibility to arrange a large scale manufacture of identical extraction units, similar to fabrication of electronic components, which leads to a very low manufacturing cost by the piece.

In the following an experimental evaluation of the present invention will be given. Samples of thermomechanical pulp (TMP) suspension diluted in water to a concentration of 1 %, being freed of coarse fibers or other particles and having a pH 3.0 to 3.5 were prepared. The TMP solution included both dissolved and colloidal substances (DCS) .

A manual extraction of the DCS sample was undertaken in order to obtain a reference. A 4.00 ml DCS sample was measured into a test tube, then 2.00 ml methyl tert-butyl - ether (MTBE) was added. The sample was vigorously shaken by hand for 2 minutes and was then centrifuged at 1500 r/min for 5 minutes. The clear MTBE-layer was carefully pipetted off. This extraction was repeated twice with two 2 ml portions of pure MTBE. The MTBE solutions were combined and then evaporated in a stream of nitrogen. The dried residue was further analyzed by gas chromatography (GC) .

Two methods of on-line flow extraction of the sample were also evaluated. First a conventional (FIA) extraction of the sample was tested in an apparatus as shown in FIG. 1. The FIA extraction apparatus consisted of a length of glass capillary 14, having an inner diameter of 150 μm, fixed by silicone glue into the side wall 22 of a glass tube 12, having an inner diameter of 1 mm,

Secondly, a high pressure flow extraction (HPFE) of the sample according to the present invention was undertaken in an apparatus as shown in FIG. 5. The HPFE apparatus was of similar construction as the FIA apparatus, but a small length of a narrow bore glass or fused silica capillary insert 46, having an inner diameter of 10 μm, was glued with polyimide resin at the inside of the end of the capillary 14, originally having a diameter of about 150 μm. The capillary insert was approx. 500 μm long.

The ancillary equipment in both examples 2 and 3 consisted of a HPLC pump, delivering 1.05 ml/min of pure MTBE to the 150 μm capillary 14. For the FIA extraction the pressure drop over the capillary was ca. 2 bar. For the HPFE the pressure drop was ca. 285 bar.

The DCS sample was pumped at a velocity of 0.70 ml/min into the 1 mm glass tube 12 using a peristaltic pump. To the outlet of the glass tube was connected a length of Teflon tubing, l m length and 0.70 mm inner diameter, to form larger segments of the phases. The apparatus was run for several minutes prior to the first sample being taken. Approx. 10 ml of the clear water phase was carefully pipetted off, then centrifuged to ensure that all of the organic phase had separated. The water phase was then manually extracted in order to determine the amount of remaining DCS.

To the dried residue of MTBE solutions from each extraction, 80μl BSTFA (bis-trimethylsilyl- trifluoroacetamide) and 40 μl TMCS (trimethylchlorosilane) was added. The solution was kept in an oven at 70°C for ₂ 0 min, and was thereafter ready for analysis by gas chromatography. The GC analysis system was set up to give directly the concentration in mg/1 of the various extractive components and component groups in the sample.

Each extraction, manual, FIA and HPFE, was repeated three times and averaged to ensure reproducibility. The results given in table 1 display the relative extraction yields of each major component group analyzed.

Table l. Yields (%) of various component groups from extraction of TMP water.

Manual FIA HPFE fatty and resin acids 84% 65% 68% lignans 61 % 81 % 86% sterols 79% 40% 88% steryl esters 77% 28% 72% triglycerides 84% <4% 82%

The results show that lignans, which are dissolved in the water phase, as well as, fatty and resin acids, being partly dissolved in water, are very well extracted with conventional flow injection systems (FIA) . Triglycerides being non-soluble in water and only being present in colloid form, are practically not extracted at all with the conventional FIA system. Triglycerides are, however, very well extracted by the new HPFE system according to the present invention.

Thus the results of the tests confirm that a dramatic improvement has been achieved with the new high pressure extraction system.

' While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments of the invention, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Thus it is e.g. to be understood that the invention may be applied to a wide variety of extractable components and solvents even if the examples mentioned earlier mainly discuss extraction of hydrophobic substances with organic solvents. It is e.g. possible to apply the invention for extracting inorganic substances, such as metal chelates, from water-based solutions. It is of course also possible to use the present invention for extraction with water from solvent based solutions.