COLUMN WITH MICROPOROUS POLYMER MEDIA

Abstract: A continuous liquid chromatographic column containing a separation medium in the form of a macroporous polymer plug is disclosed. The column possesses numerous advantages over conventional columns which are packed with beads or particles. The plug contains both small pores less than 200 nm in diameter and large pores greater than 600 nm in diameter.

Description: COLUMN WITH MACROPOROUS POLYMER MEDIA BACKGROUND OF THE INVENTION Conventional chromatography is generally carried out by the passage of a sample that is to undergo chromatographic separation through a bed of spherical beads. These beads are usually packed in a tube or column in a manner to minimize interstitial volume between the beads so as to increase the efficiency of the column. The traditional synthetic route to make spherical particles is through suspension polymerization. In this kind of polymerization the choice of monomers is lim¬ ited to those which are not soluble in the dispersion phase. Thus, the technique is not applicable to all polymers. This technique is easy to carry out, but the beads that are obtain¬ ed are of rather polydispersed sizes. Therefore, a tedious and repetitive size fractionation must generally be carried out to obtain uniformly sized beads for packing. As a result, the packing of a column in this fashion is time-consuming and expensive. To improve the efficiency of columns, the use of small particles or beads is desirable since such beads generally pack more easily leaving less interstitial volume. Synthesis of small porous beads is achievable, such as by a seeded po¬ lymerization, and such beads have been used in columns to achieve higher efficiencies. The use of increasingly smaller beads has, however, caused problems, since the smaller the beads, the shorter the column that is required. Certain prob¬ lems associated with a short column can be solved. The column volume of such short columns is reduced (resulting in a lower separation capacity) unless reduction in length is compensated for by an increase in diameter. The best results for a separa¬ tion are usually achieved when the diameter of the pores of the beads exceeds the Stockes diameter of the macromolecule to be separated by threefold or more. As a result, the beads must be very porous and therefore they are even more difficult to pack because they have a low mechanical strength. The trend to further decrease particle size in order to increase the speed and resolution of liquid chromatography columns seems to be coming to an end due to these technical limita¬ tions. Current good quality chromatographic packings possess porosities of about 50 to 60%. Methods to increase the pore volume are known but the more porous packings that would re¬ sult would likely be so brittle that their mechanical proper¬ ties would not reach the standards that are expected for HPLC. Other less conventional approaches to improve column efficien¬ cy have been tried. For example. Bio Rad manufactures Bio-Rex ® , 0.4 mm thick flexible disks comprising styrene-divinylbenzene ion-exchange resin (90%) in a Teflon ® polymer web (10% of the overall vol¬ ume) for chromatographic separation of proteins. The use of 10% Teflon, polymer, even if perfectly placed between beads, can not fully occupythe interstitial space between them, leav¬ ing some voids between particles. This will prevent the col¬ umn from reaching its theoretical maximum efficiency. PCT Publication WO 90/07965 discloses a chromatographic column plug suitable for use with gravity flow, not with pres¬ surized flow. The plug contains cracks and channels suffi¬ ciently large to permit a hydrodynamic flow. The plug com¬ prises a polymerized mixture of acrylic acid and methylenebis- acrylamide. Hjerten et al., . Chromatography, 473 (1989), 273-275, published 2 months after the filing of PCT Pub. WO 90/07965, discloses that the plugs disclosed in the PCT publi¬ cation can not be used for chromatography, since they collapse when pressure is applied. In order to solve this problem, Hjerten recommends strongly compressing the plug to increase its resolution and ability to withstand pressure. Such com¬ pression would inherently produce non-uniform channels within the plug resulting in less than ideal column efficiency. U.S. Pat. Nos. 4,889,632, 4,923,610 and 4,952,349 (Svec et al.) disclose thin layer macroporous membranes for so-call¬ ed "membrane chromatography". The membranes are punched from a macroporous sheet of polymer and the cartridge in which they are used is different from and not a column. In fact, mem¬ brane chromatography is not chromatography since there are no repeated sorption-desorption steps as the separated molecule passes through the membrane. Ku akura et al., J. Mat. Sci.. 24 (1989), 1809-13, dis¬ close a porous polymer composite column. The polymer material is produced from a combination of monomers by means of a radi¬ ation casting polymerization at -78°C. The resulting polymer material contains extremely large holes of 10 to 40 microns in diameter, and not submicron pores. As a result, column ef¬ ficiency is far less than ideal. Accordingly, none of these approaches completely solve the problems associated with conventional packed bed chroma¬ tography columns. EP 0,231,684 discloses chromatography columns with cast in place porous ceramic, i.e. inorganic, plugs which merely maintain separation media in place, either directly in liquid chromatography devices or indirectly as restrictors in super¬ critical fluid chromatographic devices. The ceramic plug is not a separation medium. Thus, it is one of the objects of the present invention to produce a separation media for use in a chromatographic column that is compact and has substantially no interstitial volume. It is another object of the present invention to produce a chromatographic column that can be prepared easily and in¬ expensively. It is a further object of the present invention to pro¬ duce a polymeric, i.e. organic, separation media from a large variety of monomers so that the separation media can be tai¬ lored to suit the end use of the column. It is a further object is the production of a continuous bed which will be a separation medium for the separation of very large entities, such as protein aggregates, micelles, or nucleic acids. Certain of these large entities cannot be sep¬ arated in a conventional packed column because they undergo degradation due to the shear forces in interstitial spaces between the packed particles. These and still further objects of the present invention will be evident from the following description of the present invention. DISCLOSURE OF THE INVENTION Accordingly, the present invention is directed to a con¬ tinuous column, preferably a chromatographic column, contain¬ ing therein at least one plug of a continuous macroporous pol¬ ymer material disposed in the column across its internal cross-sectional area. The resulting column is useful as a chromatographic column and it will also find utility in vari¬ ous catalytic, diagnostic, and absorption processes due to its ability to pass liquids therethrough. The macroporous polymer material according to this invention has a solvent regain (ability to accommodate a non-solvating solvent within its pores) of greater than about 0.1 ml/g, preferably greater than 0.5 ml/g. The materials contain not only small pores, i.e. those below about 200 nm in diameter, but also large pores, i.e. those at least about 600 nm in diameter. The plug of macroporous media that extends across the internal cross-sec¬ tional area of the column generally has a thickness of at least about 5 mm. The thickness distinguishes the plug from a mere membrane. The plug is preferably an elongated rod- shaped material having a thickness (or length) ranging from about 5 to 200 mm. While it is currently preferred to employ a single plug, multiple plugs may also be used, especially when the multiple plugs have different compositions or struc¬ tures. It is therefore possible to engineer the sorption properties within a single continuous column instead of using multiple columns in a row. Thus, the upper plug may possess suppression properties for ion chromatography of conflicting ions while the following plug performs the desired separation. The macroporous polymer plug is produced by polymerizing a polyvinyl monomer or, more preferably, a mixture of a poly- vinyl monomer and a monovinyl monomer, in the presence of an initiator and a porogen. The polymerization mixture may also contain macroporous polymeric particles. The polymerization mixture is added to the column and polymerization is initiated therein so as to form a macroporous polymer plug. The organic polymer plug is then washed with a suitable liquid to remove the porogen. A chromatographic column containing at least one macro¬ porous polymer plug separation media of this invention poss¬ esses advantages over the prior art packed columns. For exam¬ ple, the columns of the present invention are compact due to the absence of interparticular volume. This results in a very high permeability ratio and thus a very high column efficien¬ cy. The column is easy to prepare since tedious packing of beads or particles is not required. Rather, the column of the present invention is prepared using a simple polymerization process which is carried out in the presence of a porogen. Another advantage of the column of this invention is the ver¬ satility in the selection of monomer chemistry used to form the separation media. This versatility results from the flex¬ ibility of the macroporous polymer process in which a plural¬ ity of different monomers may be used. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is the ion-exchange chromatogram of chicken egg albumin on the continuous column of Example V. Fig. 2 is the ion-exchange chro atogram of chicken egg white protein on the continuous column of Example V. Fig. 3 is the ion-exchange chromatogram of model protein mixture on the continuous column of Example V. Fig. 4 is the pore size distribution curve of the plug produced in Example VI. Fig. 5 is a curve showing the relationship between back pressure and flow rate through the plug of Example VII. Fig. 6 is the gradient elution chromatogram of cytochome C, myoglobine, and chicken egg albumin, of the plug of Example VII. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS More particularly, the columns of the present invention comprise a substantially rigid tube which while preferably cy¬ lindrical may also be rectangular or polygonal. The tube may be made from any of the conventional materials used to form chromatographic columns includingmetal, glass, and rigidpol¬ ymers. Although the tube may have a limited amount of flexi¬ bility, it must be substantially rigid so that there is sub¬ stantially no change in volume of the tube during the polymer¬ ization reaction. When the tube is to be used as a liquid chromatographic column, each end of the tube is closed with a fitting for connection to a liquid chromatograph. Any con¬ ventional fitting known in the art may be used. Within the tube is disposed at least one plug of macro¬ porous organic polymer. The plug extends completely across the internal cross-sectional area of the tube so that the sam¬ ple passing through the plug, which acts as the separation media for the column, must pass through the plug. The plug is generally greater than about 5 mm thick distinguishing it from a membrane. Its overall dimension will, of course, de¬ pend upon the size of the column. Generally, the plug will have a cross-sectional area ranging from square micrometers to square meters (limited only by the size of the tube that is available) and a thickness or length of from about 5 to 200 mm or more. One plug or a plurality of plugs may be used to extend the length in the tube that is occupied by the macro¬ porous plug. When more than one plug is used they may be of the same or different sizes and/or compositions. The resulting plug, in addition to containing small pores less than about 200 nm, contains very large pores. A portion of the porosity is provided by large pores having diameters greater than about 600 nm up to about 3,000 nm. Preferably the large pores are from about 800 to 2,500 nm, more preferab¬ ly from about 800 to 2,000, and most preferably about 900 to 2,000 nm in diameter. The large pores represent at least about 10% of the total pore volume of the plug. When the large pores are less than about 10% of the total pore volume, the back pressure would be too high. Preferably the large pores represent at least about 20% of the total pore volume, since the more large pores the lower the back pressure to force a liquid therethrough. The large pores may even repre¬ sent more than 50% of the total pore volume. The small pores generally have sizes in the range of about 0.8 to 200 nm, more preferably about 1 to 100 nm. The resulting plug is also sufficiently rigid such that the plug is usable as a separation medium in a liquid chromat- ograph at the pressures at which such devices normally oper¬ ate, i.e. up to about 40 MPa (6,000 psi) . The plug has a bal¬ ance of appropriate macroporosity and physical strength that a liquid composition including one or more organic solvents and water can pass through a plug 150 mm thick under a pres¬ sure of less than about 30 MPa (4,500 psi) at a linear flow rate of at least about 200 cm/hr. Theprocess or producing the columns generally comprises (1) adding to a rigid tube sealed at both ends a deaerated po- ly erizable mixture containing aporogen; (2) polymerizing the mixture to form a macroporous polymer plug; and (3) washing the plug (or plugs) with a solvent so as to remove the porogen present in the macroporous polymer produced. The polymerizationmixture at a minimum contains at least one polyvinyl monomer, a free radical generating initiator, and a porogen. The mixture may also contain one or more mono- vinyl monomers and/or soluble polymers or insoluble macropor¬ ous polymer particles. Suitable polyvinyl monomers include divinylbenzene, di- vinylnaphthalene, divinylpyridine, alkylene dimethacrylates, hydroxyalkylenedimethacrylates, hydroxyalkylenediacrylates, oligoethylene glycol dimethacrylates, oligoethylene glycol diacrylates, vinyl esters of polycarboxylic acids, divinyl ether, pentaerythritol di-, tri-, or tetramethacrylate or ac¬ rylate, trimethylopropane trimethacrylate or acrylate, alkyl¬ ene bis acrylamides or methacrylamides, and mixtures of any such suitable polyvinyl monomers. The alkylene groups gener¬ ally contain about 1-6 carbon atoms. Monovinyl monomers which may be used include styrene, ring substituted styrenes wherein the substituents include chloromethyl, alkyl with up to 18 carbon atoms, hydroxyl, t- butyloxycarbonyl, halogen, nitro, amino group, protected hy- droxyls or amino groups, vinylnaphthalene, acrylates, methac- rylates, vinylacetate, vinylpyrolidone, and mixtures thereof. The polyvinyl monomer or polyvinyl monomer plus the monovinyl monomer are generally present in the polymerization mixture in an amount of from about 10 to 60 vol. %, and more preferab¬ ly in an amount of from about 20 to 40 vol. %. The porogen that is used may be selected from a variety of different types of materials. For example, suitable liquid porogens include aliphatic hydrocarbons, aromatic hydrocar¬ bons, esters, alcohols, ketones, ethers, solutions of soluble polymers, and mixtures thereof. The porogen is generally pres¬ ent in the polymerization mixture in an amount of from about 40 to 90 vol %, more preferably in an amount of from about 60 to 80 vol %. Soluble polymers and insoluble polymer particles may be employed in combination with the monomers. These polymers are added to the polymerization mixture prior to polymerization. The soluble polymers are dissolved out of the plug after its formation by passing a solvent through the plug. The soluble polymers serve as a polymeric porogen to increase the porosity of the final plug. Suitable soluble polymers used herein in¬ clude non-crosslinked polymers or copolymers of such monomers as styrene or ring substituted styrene, acrylates, methacryl- ates, dienes, vinylchloride, and vinylacetate. The insoluble polymer particles are used to reduce the volume shrinkage dur¬ ing the polymerization. The lesser the volume of the monomers in the polymerization mixture the smaller the contraction of volume upon polymerization. Suitable insoluble polymer parti¬ cles used herein include macroporous polymer particles which are cross-linked copolymers of the same monomers. It is, how¬ ever, presently preferred due to compatibility to employ in¬ soluble polymer particles which are formed from the same mono¬ mers used to form the polymerization mixture with which they are to be combined. The polymer particles initially have a diameter of from about 1 to 1,000 micrometers. It is not ne¬ cessary that the mixture of polymer particles have the same particle size. In fact, it is more economical and, therefore presently preferred, to use irregularly sized polymer parti¬ cles. While not necessary, the polymer particles may be soak¬ ed with a liquid immiscible with the polymerization mixture which can contain an inhibitor which inhibits free radical polymerization. This is done in order to prevent polymeriza¬ tion in the inside of the macroporous particles which would cause filling of the pores and would effectively remove them from the separation process. The rod would then contain non- porous pools unable to contribute to the separation process. Suitable inhibitors include cupric chloride and sodium ni¬ trite. The inhibitor is generally present in an amount of from about 0.001 to 1 wt %, and more preferably in an amount of from about 0.1 to 1 wt % f based on the total weight of par¬ ticles. The polymer particles are preferably degassed prior to use in the polymerization mixture. This may be accomplished by any of the conventional means known in the art. It, how¬ ever, is presently preferred to soak the particles in water, optionally containing a polymerization inhibitor, and remove the air from the pores by keeping the water-polymer particle mixture under the vacuum of a water pump for a suitable period of time such as about 5 to 20 minutes. Excess water may then be removed by filtering. The soluble polymers are generally present in an amount of from about 5 to 40% by volume of the polymerization mixture and the insoluble polymer particles in an amount of from about 5 to 50% by volume. Conventional free-radical generating polymerization ini¬ tiators may be employed to initiate polymerization. Examples of suitable initiators include peroxides such as OO-t-amyl-0- (2-ethylhexyl)monoperoxycarbonate,dipropylperoxydicarbonate, and benzoyl peroxide, as well as azo compounds such as azobis- isobutyronitrile, 2,2'-azobis(2-amidinopropane) ihydrochlor- ide, and 2,2'-azobis(isobutyramide)dihydrate. It has been found that the choice of initiator may be used as a means to control the pore distribution in a plug. Specifically, when apolymerizationwas performedwithazobisisobutyronitrilethe large pores were more than 50% of the total pore volume, but when benzoyl peroxide was substituted the large pore volume was decreased to 20% of the total pore volume. The initiator is generally present in the polymerization mixture in an amount of from about 0.2 to 5% by weight of the monomers. Prior to the addition of the polymerization mixture to the tube, the mixture is deaerated by conventional means such as bubbling an inert gas such as nitrogen into the mixture for a sufficient period of time to remove oxygen present in the mixture. Once the polymerization mixture is prepared and de- aerated, it is added to a tube sealed at both ends by suitable fittings. All of the polymerization mixture may be added and then polymerized to form a single plug. Alternatively, the polymerization mixture may be added in parts with polymeriza¬ tion being performed after each addition and before the addi¬ tion of the next part. If the same monomer mixture is used in the successive additions, a single plug column is obtained. If 2 or more different polymerization mixtures are used suc¬ cessively, the process results in 2 or more different plugs. Presently preferred is the single plug column as it affords a better match to the current conventional packed column. The multiple plug technique is difficult to apply with convention¬ al instruments and will be best used with a new chromatograph¬ ic mode that takes advantage of the special combination of dif¬ ferent separation media in one single column. Then the tube is sealed in preparation for polymerization. Once the mixture is in the tube, polymerization is car¬ ried out in a conventional manner, generally at a temperature of from about 50 to 90°C for a period of from about 6 to 24 hours, depending on the initiator and monomers used. The po¬ lymerization is preferably carried out in an inert atmosphere such as nitrogen or argon. While heating may be supplied by any means known in the art, it is presently preferred to immerse the sealed tube containing the polymerization mixture into a heated bath. Shrinkage that occurs during polymeriza¬ tion influences the overall pore structure but contact with the walls of the rigid tube is maintained. After polymerization is complete, the solid macroporous polymer plug is washed to remove any porogenic solvent and with a suitable solvent to dissolve any soluble polymer pres- ent. Suitable washing solvents include methanol, ethanol, benzene, toluene, acetone, tetrahydrofuran, and dioxan. This washing process may be done in stages; for example, by washing with a solvent, then with water and then a solvent again, or by continuous washing with a solvent. The washing step is preferably carried out by pumping the solvent through the tube filled with the macroporous polymer. In certain situations, especially those wherein it is ad¬ vantageous to the subsequent use of the column to add certain functional groups to the macroporous polymer, the polymer may be treated with a suitable material to add specific functional groups. For example, wherein themacroporous polymer compris¬ es polymerizedglycidyl methacrylate, thepolymermaybe react¬ ed with an a ine such as diethylamine to give N,N-diethylamin- o-2-hydroxypropyl (DEAHP) groups or with triethylamine hydro- chloride to give quaternary trimethylamino (Q) groups, the epoxy groups groups of the polymer may be also first hydrolyz- ed and subsequently reacted with chloroacetic acid to give carboxymethyl (CM) groups or with oleum-l,4-dioxan complex to give sulfonic (SP) groups. These groups are essential for pro¬ tein separation using ion-exchange chromatography. The macro¬ porous polymer may be provided with hydrophobic groups by the reaction with alcoholates, e.g. potassium butylate, octylate, and hexadecylate. This set of groups is essential for separa¬ tion inhydrophobic interaction and reversed-phase modes. The polymer may also react with affinants specific for a single compound or small group of compounds and then it may be used in affinity chromatography. Suitable affinants are antibod¬ ies, antigens, dyes, sugars, lectins, proteins, and nucleic acids. In a similar manner, polymers based on other monomers may also be modified and used in all of the modes of chroma¬ tography. Thereafter, the plug may be washed with a suitable solvent either stagewise or in a one-step procedure. Still another alternative relating to the washing step involves removing the polymerized plug from the tube, washing it with a suitable solvent, and then returning it to the tube. The returned polymer may be left as is or it may be swelled to occupy more space in the tube by washing the polymer with a swelling solvent such as tetrahydrofuran, 1,4-dioxan, tolu¬ ene, or halogenated hydrocarbons. After the washing step, the tube containing the macropor¬ ous polymer is ready for use. It may be used as a continuous chromatographic column as well as for catalytic, diagnostic, or absorption processes in accordance with conventional tech¬ niques known in the art. For example, when the tube is used as a chromatographic column to separate a sample into its com¬ ponents water or a buffer solution can serve as a carrier for the sample. The solution containing the sample is passed through the plug in the tube by pumping. The separation pro¬ ceeds by changing the properties of the eluent, e.g. pH, ionic strength, content of an organic solvent, and the like. The gradient of composition may have any shape such as linear, step-like, or logarithmic. Detection of the separated sample may then be accomplished by means known in the art, either in the column itself, using staining techniques, or downstream of the plug, or outside the tube as the components elute indi¬ vidually from the column. The macroporous polymer separation media according to this invention is effective for separation of materials having molecular weights ranging from about hun¬ dreds to millions. Any separation which can be done with a packed column can be performed with the column of this inven¬ tion. The present invention will now described with reference to the following non-limiting examples in which all parts and percents are by weight unless otherwise noted. EXAMPLE I One end of a stainless steel tube (4.6 mm inner diameter, 50 mm length) provided on both ends with fittings for attach¬ ment to a liquid chromatograph was closed with a steel nut stopper, the tube was purged with nitrogen and its other end was closed with a silicon rubber septum. A polymerization mixture was prepared by mixing 4.8 g glycidyl methacrylate, 3.2 g ethylene dimethacrylate, 10.8 g cyclohexanol, 1.2 g dodecanol, and 0.08 g azobisisobutyronitrile. The mixture was bubbled with nitrogen for 20 minutes to remove any oxygen present. 0.1 ml of the mixture was injected through the sep¬ tum into the tube, and polymerization was started by heating in an thermostated oil bath at 70 β C. After 7 hours the tube was removed from the bath, cooled freely to room temperature, and the septum was removed. At this point the column contain¬ ed a solid macroporous polymer plug 5 mm in length. After washing the polymer with methanol, both ends of the tube were closed with chromatographic nuts and the column attached to a HPLC chromatograph. First, methanol was pumped through the column at different flow rates. The back pressure was 0.4 MPa at a flow rate 0.5 ml/min, 0.8 MPa at 1 ml/min and 1.6 MPa at 2 ml/min. The solvent was then changed to tetrahydrofuran and the back pressure was 0.2 MPa at 0.2 ml/min and 19 MPa at 2 ml/min. The dependence of back pressure on flow rate was found to be linear. After the measurements the column was opened at the bot¬ tom and the porous polymer rod was removed using solvent pressure. EXAMPLE II A procedure the same as that of Example I was used with the exception that 0.15 ml stock solution of the polymeriza¬ tion was used. The plug after removal from the tube was 9 mm long. The plug was placed in a 50 ml round bottomed flask and 5 ml diethylamine was added. The content was refluxed for 3 hours. The epoxy groups of polymerized glycidyl methacrylate units were reacted with the a ine to give N,N-diethylamino-2- hydroxypropyl groups (DEAHP) which are essential for protein separation using ion-exchange chromatography. After the re¬ action was finished, the rod was washed with methanol, water, methanol again, and dried. The content of the DEAHP groups was found to be 1.59 mmol/g. The dry plug was put back to the tube of the column, im¬ mersed in water for 2 hours, the ends sealed with fittings and one end joined to the pump of a HPLC chromatograph while the other remained not connected to the detector. In this config¬ uration the back pressure was measured. At a flow rate of 1 ml/min the back pressure was 0.5 MPa, at 3 ml/min it was 1.3 MPa, and at 5 ml/min it was 2.2 MPa. After connecting to the UV detector the back pressure increased to 0.4 MPa at a flow rate of 0.5 ml/min. The column was washed under chromatographic conditions using a 0.02 mol/1 TRIS-HC1 buffer solution, pH = 7.3 (buffer A) at a flow rate of 0.5 ml/min until the base line did not drift any more (20 minutes) . A solution containing 0.2 lg of cytochrome C, lysozyme, yoglobin, and ovalbumin was injected through a loop and left to absorb on the continuous bed of the polymer. There was no sign of any leaking even after 20 min¬ utes of pumping the buffer solution through the column. The absorption was total. Then a gradient elution was started. The eluent was changed from buffer A linearly to a buffer so¬ lution B (1 mol/1 sodium chloride in buffer A) within a 10 min. period. Despite the fact that the chromatographic condi¬ tions far from ideal were used for this preliminary test, a separation of all four proteins was observed. The retention times of the proteins were 7.4, 7.7, 7.9, and 8.1 minutes. EXAMPLE III Into the same tube as used in Example I was injected 0.3 ml of a stock mixture consisting of 3 ml styrene, 1.2 ml divi- nylbenzene (85% of DVB) , 6 ml benzylalcohol, and 0.05 g benzo- ylperoxide. After degassing, the tube was closed and polymer¬ ization proceeded at 70°C. for 24 hours. Using a steel plung- er an 18 mm long porous polymer plug was pushed out of the tube and washed for 4 days in several portions of methanol. After the washing the plug still fit in the original tube. When the solvent was changed to tetrahydrofuran, it swelled the plug. After about 20 minutes, the diameter of the plug exceeded the diameter of the tube. In order to shrink the plug to its original size, methanol was used for subsequent exchange of the solvent. The plug was then returned to the column and methanol was again exchanged back to tetrahydro¬ furan. The swelling in the column was monitored as a change of back pressure which increased from 0.3 MPa at the beginning when the rest of the tube was still filled with methanol to more than 10 MPa after exchanging some of the solvent. At that point the measurement was terminated to prevent any pos¬ sible damage of the equipment. EXAMPLE IV A mixture of the monomers described in the Example I was degassed by bubbling nitrogen for 10 minutes. Macroporous poly[glycidyl methacrylate-co-ethylene dimethacrylate] beads were soaked with distilled water and the air was removed from their pores by keeping the water-polymer mixture under the vacuum of a water pump for 10 minutes. The beads were then filtered to remove excess water. About 1 ml of the beads were then filled in a glass vial with a flat bottom continuously purged with nitrogen and 0.5 ml of the degassed polymerization mixture was added, the dispersion was stirred with a glass rod, and the vial was sealed. The polymerization proceeded at 70°C for 6 hours. After the polymerization was finished the content of the vial seemed to be homogeneous. Due to the reaction of the epoxy groups of the glycidyl methacrylate with the silanol groups of the glass surface it was impossible to remove the block from the vial without damage of the vial. Even then, separations of the glass from the block surface was very tedious. The block does not tend to split in small pieces or to separate fragments of the original beads and the connecting copolymer. EXAMPLE V A stainless steel column (8 mm inner diameter and 50 mm length) was sealed on one end, purged with argon and its other end closed with a silicon rubber septum. A polymerization mixture was prepared by mixing 36 ml glycidyl methacrylate, 24 ml ethylene dimethacrylate, 72 ml cyclohexanol, 18 ml do- decanol, and 0.6 g azobisisobutyronitrile. The mixture was sonicated for 15 minutes under water pump vacuum and then bub¬ bled with nitrogen for another 15 minutes to remove dissolved gases. The tube of the column was completely filled with the polymerization mixture and the tube closed. The polymeriza¬ tion proceeded in a water bath at 70°C for 8 hours. After the polymerization was completed, the column was removed from the bath and left to cool to the ambient temperature. In order to wash the rod, which was 50 mm in length, the stopper on both ends of the column was changed to chromatographic fit¬ tings and the column was attached to the HPLC chromatograph. First, methanol was pumped throught the column at different flow rates to wash the rod and to test the flow through the column at the same time. The back pressure was 0.8 MPa at a flow rate 0.5 ml.min., 1.9 MPa at 1 ml.min, 4 MPa at 2 ml/min, and 13 MPa at 5 ml/min. The back pressure did not change dur¬ ing the entire washing procedure. The total amount of the methanol pumped through the column was 200 ml. The column was removed from the chromatograph and 1 ml diethylamine was injected through the inlet of the column. The inlet and outlet of the column were stopped with delrin plugs and the column was placed in a water bath ther ostated to 60°C for 3 hours. The unreacted amine was then washed out with methanol after attaching the column to the HPLC chromatograph. During the modification process the plug swells and the swoll¬ en polymer partly occupies the pores. This translates into a high back pressure at the beginning of the washing proced¬ ure. The back pressure was 32 MPa at a flow rate of 2 ml/min. and 15 MPa at 1 ml/min. After 50 minutes of washing with methanol, a 1:1 mixture of water-methanol was used. The back pressure increased to 20 MPa at a flow rate of 0.5 ml/min. After another hour the methanol-water mixture was changed to distilled water. The back pressure decreased to 6.6 MPa at a flow rate 0.5 ml/min and to 12.7 MPa at 1 ml/min. Finally, the column was washed with a 0.02 mol/1 TRIS-HC1 buffer solu¬ tion (pH 7.6) (buffer A). At a flow rate of 0.5 ml/min the back pressure was 5.7 MPa. Solutions (211) of chicken egg albumin (8 mg/ml) , chick¬ en egg white protein (16 mg/ml) , and model protein mixture (16 mg/ml) were injected through a loop and left to adsorb on the continuous macroporous polymer plug in the flow of buffer A for 10 minutes. A gradient of concentration of buffer B (1 mol/1 NAC1 in buffer A) was used for elution of the proteins at a flow rate 0.5 ml/min. The respective chromatograms shown in Figures 1-3 are for albumin (Fig. 1) , egg white protein (Fig. 2) and model protein (Fig. 3) respectively. They were detected at wave length 218 nm. As is not unusual for gradi¬ ent chromatography, the baseline of Figs. 1-3 is not flat due to the gradient of solvent composition used. The solid lines in the figures are the chromatograms, and the dashed lines were added to show the changes of solvent compositions. EXAMPLE VI A stainless steel tube 8 mm in diameter and 50 mm long was closed on one end with a silicon rubber septum and on the other with a solid silicon rubber plug. A polymerization mix¬ ture was prepared by mixing 3 ml styrene, 2 ml divinylbenzene, 7.5 ml dodecanol, and 0.5 g azobisisobutyronitrile. The mix¬ ture was deaerated by purging nitrogen for 15 min. The mix¬ ture was injected through the septum into the steel tube and polymerization was started by heating of the tube in a thermo- stated air bath at 70°C. After 20 hours the tube was removed from the hot air and slowly cooled to ambient temperature. The stoppers at both ends of the column were removed and re¬ placed with standard chromatographic column fittings. The column was attached to a chromatograph and washed with metha- nol at a flow rate of 0.1 ml/min for 1 hour and at a flow rate of 1 ml/min for 30 min. The back pressure during the second washing procedure was constantly 0.2 MPa. The column was opened at the outlet end and the polymer¬ ized rod pressed out of the column with methanol at a flow rate of 20 ml/min. The rod was dried at room temperature, crushed into smaller pieces, and evaluated for pore size dis¬ tribution of the polymer using mercury porosimetry. The dis¬ tribution curve is shown in Figure 4 and it clearly documents the presence of both small pores less than 200 nm and large pores of 1,000 nm. EXAMPLE VII A column was prepared in accordance with the procedure of Example VI except that after the washing procedures with methanol were complete, the outlet fitting of the column was connected to a UV detector. The column was equilibrated 2 hours with acetonitrile-water 1:1 mixture at a flow rate of 1 ml/min. Then the equilibration was increased in several consecutive steps up to a flow rate of 25 ml/min and the back pressure recorded. The results are shown in Figure 5 in which the linear dependence of the back pressure on the flow rate is evident. This result confirms that the continuous rod col¬ umn is useful at very high flow rates while still in the range of reasonable back pressures for use in chromatography, i.e. below about 40 MPa (6,000 psi). A solution of cytochome C, myoglobine, and chicken egg albumin was injected into the column and a gradient elution chromatography started. A linear gradient from 20% acetoni- trile in water to 60% acetonitrile in water was used. The time allowed for changing the acetonitrile concentration from the starting to the final mixture (the gradient time) was 4 minutes at a flow rate of 5 ml/min, 2 minutes at 10 ml/min, 1.3 minutes at 15 ml/min, and 0.8 minutes at 25 ml/min. The chromatograms are shown in Figure 6. COMPARATIVE EXAMPLE A The procedure of Example 1 is repeated except that the stainless steel tube is replaced by a flexible poly(tetra- fluoroethylene) tube. When the resulting tube and with its polymer plug is connected to a conventional chromatograph, essentially no flow of tetrahydrofuran through the plug is observed at pressures as high as 40 MPa (6,000 psi) . When the plug is evaluated for pore size distribution as in Example 6 by cutting the tube apart to remove the plug, no pores larger than about 200 nm are found.

Claims: What is Claimed is: 1. A continuous liquid chromatographic column compris¬ ing a rigid tube and at least one continuous plug of a macro¬ porous organic polymer disposed within the column and extend¬ ing across the cross-sectional area of the column, wherein the plug contains small pores having diameters less than about 200 nm and large pores having diameters greater than about 600 nm and wherein the large pores provide at least about 10% of the total pore volume of the plug. 2. The column of Claim 1, wherein the macroporous poly¬ mer plug has a porosity of from about 30 to 90%. 3. The column of Claim 1, wherein the tube contains two or more different plugs of macroporous polymer. 4. The column of Claim 1, wherein the macroporous poly¬ mer comprises a polymer of a polyvinyl monomer. 5. The column of Claim 1, wherein the macroporous poly¬ mer comprises a copolymer of a polyvinyl monomer and a mono¬ vinyl monomer. 6. A process for producing the column of Claim 1 which comprises the steps of (i) adding a deaerated polymerization mixture containing a porogen to a tube closed at both ends; (ii) polymerizing the mixture to form a macroporous organic polymer plug, and (iii) washing the macroporous polymer plug to remove the porogen and to produce the plug containing small pores having diameters less than about 200 nm and large pores having diameters greater than about 600 nm. 7. The process of Claim 6, wherein the polymerization mixture is added in at least two portions, with polymerization being performed on each of the portions prior to the addition of the next portion. 8. The process of Claim 6, wherein at least two differ¬ ent polymerization mixtures are added consecutively, with po¬ lymerization being performed on each of the mixtures prior to the addition of the next mixture. 9. The process of Claim 6, wherein the washing step is performed while the plug is in the tube. 10. The process of Claim 6, wherein the washing step is performed by first removing the plug from the tube, washing the plug, followed by returning the plug to the tube. 11. The process of Claim 10, wherein the plug is swelled after it is returned to the tube. 12. The process of Claim 6, wherein the polymerization mixture comprises a polyvinyl monomer, an initiator, and a porogen. 13. The process of Claim 12, wherein the polymerization mixture further comprises a monovinyl monomer. 14. The process of Claims 12 and 13, wherein the polym¬ erization mixture further comprises a polymer. 15. The process of Claim 14, wherein the polymer is a soluble polymer. 16. The process of Claim 14, wherein the polymer is in¬ soluble polymer particles. 17. The process of Claim 16, wherein the polymer parti¬ cles are soaked with a liquid immiscible with the polymeriza¬ tion mixture prior to combining therewith. 18. The process of Claim 16, wherein the insoluble poly- mer particles are macroporous and are formed from the same mon¬ omer as is present in the polymerization mixture. 19. A process of separating compounds by liquid chroma¬ tography which comprises use of the column of Claims 1 to 5. 20. A column comprising a rigid tube and at least one continuous plug of a macroporous organic polymer disposed within the column and extending across the cross-sectional area of the column, wherein the plug contains small pores hav¬ ing diameters less than about 200 nm and large pores having diameters greater than about 600 nm and wherein said column is capable of passing a liquid selected from an organic sol¬ vent and water therethrough at a linear flow rate of at least about 200 cm/hr and at a pressure of less than about 30 MPa (4,500 psi) . 21. The column of Claim 20, wherein the large pores pro¬ vide at least about 10% of the total pore volume of the plug. 22. The column of Claim 20, wherein the macroporous pol¬ ymer comprises a polymer of a polyvinyl monomer. 23. The column of Claim 20, wherein the macroporous pol¬ ymer comprises a copolymer of a polyvinyl monomer and a mono¬ vinyl monomer.

Inventors: FRECHET JEAN M J, SVEC FRANTISEK, FRECHET, JEAN, M., J., SVEC, FRANTISEK
Applicants: CORNELL RES FOUNDATION INC, CORNELL RESEARCH FOUNDATION, INC.
Application year: 1992
Main classification: G01N30
IPC codes: B01D15, B01J20, G01N30