Modified poly(glycidyl methacrylate-co-ethylene dimethacrylate) continuous rod columns for preparative-scale ion-exchange chromatography of proteins

Exploiting immobilized metal affinity membranes for the isolation or purification of therapeutically relevant species

Increasing reports regarding the isolation or purification of biospecies for therapeutic purpose using the immobilized metal affinity chromatography have been presented in recent years. At the same time, membrane chromatography technique has also gained more and more attention for their advantage in speeding the separation process. The immobilized metal affinity membrane technique developed by combining these two techniques may provide an alternative potential tool for separating the therapeutically relevant biospecies. In this review paper, the features of the immobilized metal affinity membranes are discussed and concentrated on three subtopics: membrane matrices, immobilized metal affinity method, and membrane module designs. Several examples of practically applying the immobilized metal affinity membranes on the purification of potential therapeutics reported in the literature are subsequently presented. Lastly, this review also provides an overall evaluation on the possible advantages and problems existing in this technique to point out opportunities and further improvements for more applied development of the immobilized metal affinity membranes.

Comparison between adsorption isotherm determination techniques and overloaded band profiles on four batches of monolithic columns

The adsorption isotherms of 4-tert.-butyl phenol were measured on four different monolithic columns, using three different techniques, classical frontal analysis (FA), the perturbation on a plateau method (PP) and the recently introduced numerical procedure known as the inverse numerical method (IN). This last approach requires only the recording of a few overloaded profiles and has the potential advantage of affording a dramatic decrease of the amounts of compounds, solvent, and time needed to determine accurate estimates of the coefficients of the isotherm. The reproducibility of the adsorption data measured on the four columns is discussed with reference to the specific techniques used for obtaining these data and to the most suitable equation used for modeling them. The data obtained for the different columns were highly consistent. The inverse numerical approach was confirmed to provide a powerful, accurate, and economic method for measuring single component adsorption data.

High-performance affinity chromatography with immobilization of protein A and L-histidine on molded monolith

Reactive monoliths of macroporous poly(glycidyl methacrylate-co-ethylene dimethacrylate) have been prepared by "in-situ" copolymerization of the monomers in the presence of porogenic diluents. Protein A and L-histidine were immobilized on the monoliths directly or through a spacer arm, respectively. The properties of these two kinds of affinity columns were characterized, and the results showed that the columns with coupling of ligands by a spacer arm have some extent of non-specific adsorption for bovine serum albumin. The affinity column based on the monolithic polymer support provided us with good hydrodynamic characteristic, low flow resistance, and easy preparation. These two affinity columns were used for the purification of immunoglobulin G from human serum. The purity of the purified IgG was detected by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS). The stability of the protein A affinity column was investigated, and its performance remained invariable after half a year. The effects of the nature and the pH of the buffer system on the adsorption capacity of human IgG on histidyl affinity column were also investigated. The protein A affinity column is favorable for rapid analysis of human IgG samples. In contrast, the advantages of mild elution conditions, high stability, as well as low cost provide the histidyl column further potential possibility for fast removal of IgG from human plasma in clinical applications.

High-performance affinity chromatography for characterization of human immunoglobulin G digestion with papain

Reactive continuous rods of macroporous poly(glycidyl methacrylate-co-ethylene dimethacrylate) were prepared within the confines of a stainless steel column. Then papain was immobilized on these monoliths either directly or linked by a spacer arm. In a further step, a protein A affinity column was used for the characterization of the digestion products of human immunoglobulin G (IgG) by papain. The results showed that papain immobilized on the monolithic rod through a spacer arm exhibits higher activity for the digestion of human IgG than that without a spacer arm. The apparent Michaelis-Menten kinetic constants of free and immobilized papain, K(m) and V(max), were determined. The digestion conditions of human IgG with free and immobilized papain were optimized. Comparison of the thermal stability of free and immobilized papain showed that the immobilized papain exhibited higher thermal stability than the free enzyme. The half-time of immobilized papain reaches about a week under optimum pH and temperature conditions.

Porous polymer monoliths: an alternative to classical beads

Porous polymer monoliths are a new category of materials developed during the last decade. These materials are prepared using a simple molding process carried out within the confines of a closed mold. Polymerization of a mixture that typically contains monomers, free-radical initiator, and porogenic solvent affords macroporous materials with large through-pores that enable flow-through applications. The versatility of the preparation technique is demonstrated by its use with hydrophobic, hydrophilic, ionizable, and zwitterionic monomers. The porous properties of the monolith can be controlled over a broad range. These, in turn, determine the hydrodynamic properties of the devices that contain the molded media. Since all the mobile phase must flow through the monolith, the mass transport within the molded material is dominated very much by convection, and the monolithic devices perform well even at very high flow rates. The applications of monolithic materials are demonstrated on the chromatographic separation of biological compounds and synthetic polymers, electrochromatography, gas chromatography, enzyme immobilization, molecular recognition, and in advanced detection systems. Grafting of the pore walls with selected polymers leads to materials with completely changed surface chemistries.

Chromatographic reactors based on biological activity

In the last decade there were many papers published on the study of enzyme catalyzed reactions performed in so-called chromatographic reactors. The attractive feature of such systems is that during the course of the reaction the compounds are already separated, which can drive the reaction beyond the thermodynamic equilibrium as well as remove putative inhibitors. In this chapter, an overview of such chromatographic bioreactor systems is given. Besides, some immobilization techniques to improve enzyme activity are discussed together with modern chromatographic supports with improved hydrodynamic characteristics to be used in this context.

Short monolithic columns as stationary phases for biochromatography

Monolithic supports represent a novel type of stationary phases for liquid and gas chromatography, for capillary electrochromatography, and as supports for bioconversion and solid phase synthesis. As opposed to individual particles packed into chromatographic columns, monolithic supports are cast as continuous homogeneous phases. They represent an approach that provides high rates of mass transfer at lower pressure drops as well as high efficiencies even at elevated flow rates. Therefore, much faster separations are possible and the productivity of chromatographic processes can be increased by at least one order of magnitude as compared to traditional chromatographic columns packed with porous particles. Besides the speed, the nature of the pores allows easy access even in the case of large molecules, which make monolithic supports a method of choice for the separation of nanoparticles like pDNA and viruses. Finally, for the optimal purification of larger biomolecules, the chromatographic column needs to be short. This enhances the speed of the separation process and reduces backpressure, unspecific binding, product degradation and minor changes in the structure of the biomolecule, without sacrificing resolution. Short Monolithic Columns (SMC) were engineered to combine both features and have the potential of becoming the method of choice for the purification of larger biomolecules and nanopartides on the semi-preparative scale.

Adsorption equilibria of butyl- and amylbenzene on monolithic silica-based columns

The adsorption isotherms of butyl- and amylbenzene on silica monolithic columns were measured by frontal analysis. The external, internal and total porosities of these columns were determined by inverse size-exclusion chromatography. The adsorption isotherms are concave upward in the entire concentration range investigated. They were fitted to the anti-Langmuir model, an unusual model in liquid-solid and liquid-liquid phase equilibria. Band profiles under overloaded conditions were recorded. They were in good agreement with the profiles calculated using th,e lumped pore diffusion model of chromatography and these adsorption isotherms.

Monolithic stationary phases for liquid chromatography and capillary electrochromatography

A monolithic stationary phase is the continuous unitary porous structure prepared by in situ polymerization or consolidation inside the column tubing and, if necessary, the surface is functionalized to convert it into a sorbent with the desired chromatographic binding properties [J. Chromatogr. A 855 (1999) 273]. Monolithic stationary phases have attracted considerable attention in liquid chromatography and capillary electrochromatography in recent years due to their simple preparation procedure, unique properties and excellent performance, especially for separation of biopolymers. This review summarizes the preparation, characterization and applications of the monolithic stationary phases. In addition, the disadvantages and limitations of the monolithic stationary phases are also briefly discussed.

Urea-formaldehyde resin monolith as a new packing material for affinity chromatography

A urea-formaldehyde resin (UF) continuous bed has been prepared through in-situ condensation polymerization in a confined tube. The monolith is an agglomerate of 2-microm irregular particles. Nitrogen adsorption shows that the monolith has a bimodal pore size distribution. It has low resistance to flow. A dyed monolith is obtained through modification of the UF monolith with Cibacron blue F3GA. Although its dye concentration and dynamic capacity are low compared to Sepharose type affinity media, the dyed monolith can separate some proteins in the affinity mode of liquid chromatography.

Direct synthesis of peptides on convective interaction media monolithic columns for affinity chromatography

Solid-phase peptide synthesis was performed on glycidyle methacrylate-co-ethylene dimethacrylate monoliths using Fmoc chemistry. The native epoxy groups were amino-functionalized by reaction with ethylenediamine or ammonia ions. A peptide directed against human blood coagulation factor VIII was synthesized as a model peptide. Amino acid analysis revealed the correct amino acid ratio as present in the sequence. The ligand density of 5 micromol/mL was equal to that achieved with conventional peptide immobilization via epoxy groups. These supports were directly used as peptide affinity chromatography matrixes. The functionality of the CIM monolithic supports was proven by affinity chromatography of factor VIII. The ammonia-functionalized support performed with low hydrophobicity and did not show unspecific adsorption of proteins.

Affinity membrane chromatography for the analysis and purification of proteins

Affinity chromatography is unique among separation methods as it is the only technique that permits the purification of proteins based on biological functions rather than individual physical or chemical properties. The high specificity of affinity chromatography is due to the strong interaction between the ligand and the proteins of interest. Membrane separation allows the processing of a large amount of sample in a relatively short time owing to its structure, which provides a system with rapid reaction kinetics. The integration of membrane and affinity chromatography provides a number of advantages over traditional affinity chromatography with porous-bead packed columns, especially with regard to time and recovery of activity. This review gives detailed descriptions of materials used as membrane substrates, preparation of basic membranes, coupling of affinity ligands to membrane supports, and categories of affinity membrane cartridges. It also summarizes the applications of cellulose/glycidyl methacrylate composite membranes for proteins separation developed in our laboratory.

Chromatographic separation of proteins on metal immobilized iminodiacetic acid-bound molded monolithic rods of macroporous poly(glycidyl methacrylate-co-ethylene dimethacrylate)

Continuous rod of macroporous poly(glycidyl methacrylate-co-ethylene dimethacrylate) was prepared by a free radical polymerization within the confines of a stainless-steel column. The epoxide groups of the rod were modified by a reaction with iminodiacetic acid (IDA) that affords the active site to form metal IDA chelates used for immobilized metal affinity chromatography (IMAC). The efficiency of coupling of IDA to the epoxide-contained matrix was studied as a function of reaction time and temperature. High-performance separation of proteins, based on immobilized different metals on the column, were described. The influence of pH on the adsorption capacity of bovine serum albumin on the Cu2+-IDA continuous rod column was investigated in the range from 5.0 to 9.0. Purification of lysozyme from egg white and human serum albumin (HSA) on the commercially available HSA solution were performed on the naked IDA and Cu2+-IDA continuous rod columns, respectively; and the purity of the obtained fractions was detected by matrix-assisted laser desorption-ionization time-of-flight mass spectrometry.

Capillary electrochromatography in anion-exchange and normal-phase mode using monolithic stationary phases

Hydrophilic macroporous weak and strong anion-exchange stationary phases have been prepared in a monolithic format within untreated fused-silica capillaries by the simple thermally or UV-initiated polymerization of 2-dimethylaminoethyl methacrylate, 2-hydroxyethyl methacrylate and ethylene dimethacrylate in the presence of a binary porogenic mixture of dodecanol and cyclohexanol. The tertiary amino functionalities were then alkylated in situ to afford strong anion-exchangers. These new monolithic stationary phases with optimized porous properties were used for the CEC separation of various organic anions. Thus, a mixture of 2-substituted propionic acid drugs (profens) was separated in 13 min and high column efficiencies of up to 231,000 plates/m were achieved. The separation of substituted benzoic acids indicates that the selectivity results primarily from the anion-exchange interactions, while electrophoretic migration contributes only slightly. In addition, these hydrophilic anion-exchangers are also able to separate weakly acidic, neutral and basic compounds such as phenols, xanthines and aromatic amines in normal-phase electrochromatographic mode.

New synthetic ways for the preparation of high-performance liquid chromatography supports

The latest developments and in particular important synthetic aspects for the preparation of modern HPLC supports are reviewed. In this context, the chemistry of inorganic supports based on silica, zirconia, titania or aluminum oxide as well as of organic supports based on poly(styrene-divinylbenzene), acrylates, methacrylates and other, more specialized polymers is covered. Special consideration is given to modern approaches such as sol-gel technology, molecular imprinting, perfusion chromatography, the preparation of monolithic separation media as well as to organic HPLC supports prepared by new polymer technologies such as ring-opening metathesis polymerization. Synthetic particularities relevant for the corresponding applications are outlined.

Poly(glycidyl methacrylate-divinylbenzene-triallylisocyanurate) continuous-bed protein chromatography

A novel continuous bed with high dynamic adsorption capacity for protein has been developed. It is a macroporous poly(glycidyl methacrylate-divinylbenzene-triallylisocyanurate) rod prepared by in situ copolymerization in a chromatographic tube. The bed matrix contained epoxy groups, so diethylaminohydroxypropyl groups were coupled to the matrix, leading to an anion-exchange continuous bed. The component, specific surface area, and the pore structure of the bed matrix were characterized by Fourier transform infrared spectroscopy, BET method and scanning and transmission electron microscopies, respectively. The flow properties, column efficiency and the dynamic adsorption behavior of the bed were studied. The results show that the continuous bed, a ternary copolymer of glycidyl methacrylate (GMA), divinylbenzene (DVB) and triallylisocyanurate (TAIC) with a specific surface area of 56.4 m2/g, consisted of a three-dimensional structure made up of continuous clusters of microspheres (300 nm) and interconnected irregular pores. The rate of mass transfer is enhanced by the convection of the mobile phase through the pores. The dynamic adsorption isotherm of the anion-exchange column for bovine serum albumin was expressed by the Langmuir equation with a dynamic capacity as high as 76.0 mg/g. Moreover, the separation of proteins, i.e. lysozyme, hemoglobin and bovine serum albumin, is little affected by mobile-phase velocity up to 902.5 cm/h; it was completed within 5 min at 902.5 cm/h.

Monoliths as stationary phases for separation of proteins and polynucleotides and enzymatic conversion

Monoliths are considered as a novel generation of stationary phases. They were applied for capillary electrochromatography and liquid chromatography exploiting every action principle such as ion-exchange, affinity recognition, reversed-phase, and hydrophobic interaction. The fast separation was explained by convective transport of the solutes through the bed. The contribution of this mode of transport is similarly explained as done for the beds packed with particles with gigapores. For monolithic beds, the concept of an ultrashort bed was frequently used. This mode of operation allows very short separation time. In many cases a gradient elution is necessary to achieve separation. Examples of applications for protein and polynucleotide separation performed on monoliths are given. Enzymatic conversion was described showing the examples of several immobilzed enzymes.

Grafted macroporous polymer monolithic disks: a new format of scavengers for solution-phase combinatorial chemistry

Polyethylene encased porous poly(chloromethylstyrene-co-divinylbenzene) disks have been prepared by polymerization in a cylindrical glass mold and cut to a disk format. Following attachment of a free radical azo initiator 4,4'-azobis(4-cyanovaleric acid) to available functionalities at the surface of the pores, the polymerization of 2-vinyl-4,4-dimethylazlactone was initiated from the surface. To avoid an undesirable increase in flow resistance and to improve the yield of grafting, divinylbenzene was added to the polymerization mixture in order to form a layer of swellable reactive polymer gel within the pores. The use of these disks as scavenging filters to remove various amines from solutions in flow-through operations was demonstrated by effective removal of amines in a very short period of time from their solutions in a variety of solvents, even including alcohols and water.

Solid-phase trapping of solutes for further chromatographic or electrophoretic analysis

Because of its simplicity, speed and effectiveness, solid-phase extraction (SPE) has become the preferred technique for concentration of selected analytes prior to chromatographic or electrophoretic analysis. In this review the historical development of SPE is briefly traced. Then the principles of SPE are reviewed in some detail. Numerous references are given on the format, sorbents, elution conditions, online techniques and automation with special emphasis on relatively recent developments. The principles and recent advances in solid-phase microextraction (SPME) are also reviewed. The final section on selected recent applications includes an extensive list of references to work published within the last three years. Future trends and developments are discussed briefly.

Construction of large-volume monolithic columns

Monolithic supports have become the subject of extensive study in the past years. Despite their advantageous features and many successful chromatographic applications in the analytical scale, only a very few examples of larger volume monoliths were described. In the case of GMA-EDMA monoliths, this can be attributed to the fact that due to the exothermic polymerization a pronounced temperature increase inside the monolith significantly affects the structure. The temperature increase depends on the thickness of the monolith, and consequently, there is an upper limit that allows the preparation of a unit with a uniform structure. In the present work, we have analyzed a heat release during the polymerization and have derived a mathematical model for the prediction of the maximal thickness of the monolithic annulus having a uniform structure. On the basis of the calculations, two annuluses of different diameters were polymerized and merged into a single monolithic unit with a volume of 80 mL. In addition, a special housing was designed to provide a uniform flow distribution in the radial direction over the entire monolith bed. It was shown that such a monolithic column exhibits flow-independent separation efficiency and dynamic binding capacity up to flow rates higher than 100 mL/min. The separation and loading times are in the range of a few minutes. The pressure drop on the column is linearly dependent on the flow rate and does not exceed 2.5 MPa at a flow rate of 250 ml/min.

Sol-gel monolithic columns with reversed electroosmotic flow for capillary electrochromatography

Sol-gel chemistry was used to prepare porous monolithic columns for capillary electrochromatography. The developed sol-gel approach proved invaluable and generates monolithic columns in a simple and rapid manner. Practically any desired column length ranging from a few tens of centimeters to a few meters may be readily obtained. The incorporation of the sol-gel precursor, N-octadecyldimethyl[3-(trimethoxysilyl)propyl]ammonium chloride, into the sol solution proved to be critical as this reagent possesses an octadecyl moiety that allows for chromatographic interactions of analytes with the monolithic stationary phase. Additionally, this reagent served to yield a positively charged surface, thereby providing the relatively strong reversed electroosmotic flow (EOF) in capillary electrochromatography. The enhanced permeability of the monolithic capillaries allowed for the use of such columns without the need for modifications to the commercial CE instrument. There was no need to pressurize both capillary ends during operation or to use high pressures for column rinsing. With the developed procedure, no bubble formation was detected during analysis with the monolithic capillaries when using electric field strengths of up to 300 V cm(-1). The EOF in the monolith columns was found to be dependent on the percentage of organic modifier present in the mobile phase. Separation efficiencies of up to 1.75 x 10(5) plates/m (87,300 plates/column) were achieved on a 50 cm x 50 microm i.d. column using polycyclic aromatic hydrocarbons and aromatic aldehydes and ketones as test solutes.

Separation of oligonucleotides on novel monolithic columns with ion-exchange functional surfaces

Porous monolithic columns have been prepared by the direct free radical copolymerization of glycidyl methacrylate and ethylene dimethacrylate within the confines of a 50x8 mm I.D. chromatographic column in the presence of porogens. The epoxide groups of these monoliths were modified to different extents by reaction with diethylamine to afford 1-N,N-diethylamino-2-hydroxypropyl functionalities useful for ion-exchange chromatography. Following characterization of the monoliths, the columns were tested in the chromatographic separation of a homologous series of oligodeoxyadenylic [pd(A)(12-18)] and oligothymidylic acids [d(pT)(12-24)] at different flow-rates. Very good separations of the oligonucleotides were achieved even at the high flow-rate of 4 ml/min.

Network modeling of the convective flow and diffusion of molecules adsorbing in monoliths and in porous particles packed in a chromatographic column

A cubic lattice network of interconnected pores was constructed to represent the porous structure existing in a monolith (continuous bed) or in a column packed with porous chromatographic particles. Expressions were also constructed and utilized to simulate, through the use of the pore network model, the intraparticle interstitial velocity and pore diffusivity of adsorbate molecules in porous chromatographic particles or in monoliths under retained and unretained conditions. The combined effects of steric hindrance at the entrance to the pores and frictional resistance within the pores, as well as the effects of pore size, pore connectivity, nT, of the porous network, molecular size of adsorbate and ligand (active site), and the fractional saturation of adsorption sites (ligands), have been considered. The results for the adsorption systems studied in this work, indicate that the obstruction effects on the intraparticle interstitial velocity, due to (a) the thickness of the immobilized layer of active sites and (b) the thickness of the adsorbed layer, are small and appear to be insignificant when they are compared with the very significant effect that the value of the pore connectivity, nT, has on the magnitude of the intraparticle interstitial velocity. The effective pore diffusion coefficient of the adsorbate molecules was found to decline with increasing molecular size of ligand, with increasing fractional saturation of the active sites or with diminishing pore size, and with decreasing pore connectivity, nT. The results also show that the magnitude of the interstitial fluid velocity is many times larger than the diffusion velocity of the adsorbate molecules within the porous adsorbent particles. Furthermore, the results clearly show that the intraparticle interstitial velocity and the pore diffusivity of the adsorbate increase significantly as the value of the pore connectivity, nT, of the porous medium increases. The results of this work indicate that the pore network model and the expressions presented in this work, could allow one, for a given porous adsorbent, adsorbate, ligand (active site), and interstitial column fluid velocity, to determine in an a priori manner the values of the intraparticle interstitial velocity and pore diffusivity within the monolith or within the porous adsorbent particles as the fractional saturation of the active sites changes. The values of these transport parameters could then be employed in the macroscopic models that could predict the dynamic behavior, scale-up, and design of chromatographic systems. The theoretical results could also have important implications in the selection of a ligand as well as in the selection and construction of an affinity porous matrix.

Continuous superporous agarose beds for chromatography and electrophoresis

Continuous agarose beds (monoliths) were prepared by casting agarose emulsions designed to generate superporous agarose. The gel structures obtained were transected by superpores (diameters could be varied in the range 20-200 microns) through which liquids could be pumped. The pore structure and the basic properties of the continuous gel were investigated by microscopy and size exclusion chromatography. The chromatographic behaviour was approximately the same as for beds packed with homogeneous agarose beads with a particle diameter equivalent to the distance between the superpores. In one application, the superporous continuous agarose bed was derivatized with a NAD+ analogue and used in the affinity purification of bovine lactate dehydrogenase from a crude extract. In another application, a new superporous composite gel material was prepared by adding hydroxyapatite particles to the agarose phase. The composite bed was used to separate a protein mixture by hydroxyapatite chromatography. In a third application, the continuous superporous agarose material was used as an electrophoresis gel. Here, a water-immiscible organic liquid was pumped through the superpores to dissipate the joule heat evolved, thus allowing high current densities.

New packing materials for protein chromatography

This review describes new packing materials designed for protein chromatography, covering advances in base supports and stationary phases. Base supports are classified according to their chemical composition. Since most separation media are bead shaped, typical procedures used for their preparation are also presented. In order to provide matrices combining improved chemical stability and chromatographic performances, composite materials continue to be developed, including bonded stationary phases, pore composites and mixed carriers. The different approaches to their preparation are described and characteristics that play a major role in the chromatographic process are discussed. Recently introduced materials and some of their applications under non-denaturing conditions in the different chromatographic modes are also presented.

Rigid porous polyacrylamide-based monolithic columns containing butyl methacrylate as a separation medium for the rapid hydrophobic interaction chromatography of proteins

Macroporous poly(acrylamide-co-butyl methacrylate-co-N,N'-methylenebisacrylamide) monoliths containing up to 15% butyl methacrylate units have been prepared by direct polymerization within the confines of HPLC columns. The hydrodynamic and chromatographic properties of these 50 mm x 8 mm I.D. columns-such as back pressure at different flow-rates, effect of percentage of hydrophobic component in the polymerization mixture, effect of salt concentration on the retention of proteins, dynamic loading capacity, and recovery-were determined under conditions typical of hydrophobic interaction chromatography. Using the monolithic column, five proteins were easily separated within only 3 min.

Application of compact porous tubes for preparative isolation of clotting factor VIII from human plasma

Membranes as well as compact porous disks are successfully used for fast analytical separations of biopolymers. So far, technical difficulties have prevented the proper scaling-up of the processes and the use of membranes and compact disks for preparative separations in a large scale. In this paper, the use of a compact porous tube for fast preparative separations of proteins is shown as a possible solution to these problems. The units have yielded good results, in terms of performance and speed of separation. The application of compact porous tubes for the preparative isolation of clotting factor VIII from human plasma shows that this method can even be used for the separation of very sensitive biopolymers. As far as yield and purity of the isolated proteins are concerned, the method was comparable to preparative column chromatography. The period of time required for separation was five times shorter than with corresponding column chromatographic methods. Compact porous disks made of the same support material can also be used for in-process analysis in order to control the separation. The quick response, which is obtained from these units within 5 to 60 s, allows close monitoring of the purification process.

Molded continuous poly(styrene-co-divinylbenzene) rod as a separation medium for the very fast separation of polymers. Comparison of the chromatographic properties of the monolithic rod with columns packed with porous and non-porous beads in high-performance liquid chromatography of polystyrenes

Gradient elution separations of polystyrene standards in a monolithic molded 50 x 8 mm I.D. poly(styrene-co-divinylbenzene) rod column and in 50 x 8 mm I.D. and 30 x 4.1 mm I.D. columns packed with porous and non-porous poly(styrene-co-divinylbenzene) beads has been carried out. All of these separation media differ in shape and porosity. Excellent separations of eight polystyrene standards were achieved with both the molded monolithic rod and porous beads at moderate flow-rates. However, the monolithic medium proved to be superior for high-speed separations using very steep gradients at a flow-rate of 20 ml/min. Three polystyrene standards were separated in the rod column within 4 s. The separation in the column packed with non-porous beads was poor at flow-rates of 2-8 ml/min, while higher flow-rates led to an unacceptably high back pressure.

New formats of polymeric stationary phases for HPLC separations: molded macroporous disks and rods

A molding process has been used for the preparation of separation media in different shapes such as rods and flat membrane-like disks. The polymerization is carried out using a mixture of monomers, porogenic solvent and free-radical initiator under conditions that afford macroporous materials with through-pores or channels large enough to provide the high flow characteristics required for applications in chromatography. In contrast to classical suspension polymerization, the solubility of monomers in water does not restrict their use. The versatility of the preparation technique is demonstrated in polymerizations involving both hydrophobic and hydrophilic monomers such as styrene, chloromethylstyrene, glycidyl methacrylate, alkyl methacrylates and acrylamide. Techniques have been developed that allow fine control of the porous properties of the polymers. These, in turn, determine the hydrodynamic properties of the separation devices that contain the molded media. Since all the mobile phase must flow through the separation medium, the mass transport within the molded media is accelerated considerably by convection. Therefore, the separations can be performed at much higher flow rates than in packed columns. This is particularly important for separations of large molecules such as proteins for which diffusion is a serious problem that significantly slows down the separation processes. The molded separation media have been used for the separation of biological compounds using gentle chromatographic modes such as hydrophobic interaction, ion-exchange and affinity chromatography during which the biological activity of the separated compounds is completely retained.