Rapid protein profiling with a novel anion-exchange material

Recent developments in analytical chromatography

Capillary gas chromatography (GC) is rapidly reaching a state of maturity. Recent advances in GC include new highly selective and stable open-tubular columns, capillary sampling techniques, and element-sensitive (plasma) detectors. An impressive growth of modern liquid chromatography continues with an emphasis on the separations of biopolymers, new silica-based and stable polymeric packings, microcolumn techniques, electroosmotically driven separations, and ultrasensitive detection. Supercritical fluid chromatography has gained considerable attention primarily because of its distinctive detection capabilities. Novel combinations of chromatographic techniques with each other, or with spectroscopic methods, continue to be explored.

Protein separation using non-porous sorbents

This article overviews the development of non-porous sorbents having small particle diameters which have proven effective for rapid analysis and micropreparative separation of proteins by liquid chromatography. Much attention is given to the preparation and application of silica- and polystyrene-based non-porous packings for various chromatographic modes, especially affinity chromatography. Modeling works on the prediction and parameter estimation for the dynamics of protein adsorption using non-porous sorbents are reviewed and briefly described. To conclude this review, future prospects of the application of non-porous sorbents are also presented.

High-speed high-performance liquid chromatography of peptides and proteins

Over the last thirty years the name HPLC has been synonymous with high-speed liquid chromatography and during the last ten years we have experienced a dramatic increase in the speed of analysis particularly as far as the separation of biological macromolecules, such as proteins, is concerned. With a solid grounding in the chromatographic theories, column technology has been mainly responsible for the advances in this field. Recent development shows that columns packed with micropellicular or gigaporous stationary phases of the bidisperse or the bimodal type facilitate rapid mass transfer between the mobile and stationary phases and thus can deliver high resolution separations in a very short time. This suggest that HPLC has the potential to be the prime analytical technique for on-line monitoring of biotechnological processes in real time. Further enhancement of the speed of separation comes from the use of elevated temperatures. The role of temperature in HPLC has largely been ignored and most commercial instruments are not equipped with appropriate temperature control. Results presented here strongly suggest, however, that elevated column temperature may find increasing use in the HPLC of large molecules. In such analytical applications temperature programming may also play a major role provided columns with low heat capacity, such as packed fused-silica capillaries, gain wider employment in HPLC.

Rapid analysis of somatostatin in pharmaceutical preparations by HPLC with a micropellicular reversed-phase column

A rapid high-performance liquid chromatography method for the analysis of somatostatin in pharmaceutical preparations is described. A commercially available column packed with 2 microns spherical non-porous silica-based reversed-phase sorbent is used, along with a mobile phase consisting of acetonitrile and aqueous phosphoric acid, adjusted to pH 2.8 with sodium hydroxide. The effect of the organic modifier content and column temperature on the retention behaviour of somatostatin is reported. The method is found to be highly selective and specific, as indicated by the baseline separation of a mixture containing somatostatin and two analogue peptides, which differ from the analyte for one and two amino acids, respectively. Down to 10 ng of somatostatin can be detected and the detector response is linear over the concentration range from 4.14 to 20.75 micrograms ml-1. The application of this method to two commercial pharmaceutical formulations of somatostatin is found to give a mean percentage recovery from each of the two commercial samples, subjected to multiple injection analysis (n = 5), of 100.9% with a RSD of 0.92%, and 102.6% with a RSD of 1.56%, respectively.

Reversed-phase liquid chromatography with microspherical octadecyl-zirconia bonded stationary phases

Microspherical zirconia particles were synthesized and surface modified with octadecylsilane compounds for reversed-phase high-performance liquid chromatography. Monomeric and "polymeric" octadecyl-zirconia bonded stationary phases were obtained by reacting the support with octadecyldimethylchlorosilane or octadecyltrichlorosilane, respectively. The surface coverage of the zirconia-based stationary phases with octadecyl functions was approximately the same as that of octadecyl-silica sorbents. These phases were evaluated in terms of reversed-phase chromatographic properties with non-polar, slightly polar and ionic species over a wide range of mobile phase composition and pH. Monomeric octadecyl-zirconia with end-capping exhibited some metallic interactions with both basic and acidic solutes, but these interactions were greatly reduced in the presence of competing agents (e.g., tartrate ions) in the mobile phase. The "polymeric" octadecyl-zirconia sorbents exhibited higher retention than the monomeric ones with the various solutes investigated, and their residual absorptivities toward acidic solutes were much lower. The retention of non-polar and slightly polar aromatic compounds was quasi-homoenergetic on both types of octadecyl-zirconia stationary phases. Stability studies conducted at extreme pH conditions (pH 2.0 and pH 12.0), have shown that "polymeric" octadecyl-zirconia sorbents are more stable than their monomeric counterparts. These stationary phases were quite useful in the separation of polycyclic aromatic hydrocarbons, alkylbenzene and phenyl alkylalcohol homologous series, oligosaccharides, dansyl-amino acids, peptides and proteins.

Fimbriated stationary phases for proteins

This paper describes synthetic procedures for preparing fimbriated stationary phases on poly(styrene-divinylbenzene) (PS-DVB) packing materials. The synthesis consists of a five-step procedure in which the order in which the steps are carried out may be varied. These steps are (i) polymerization of monomers to form an amphiphilic copolymer or oligomer, (ii) adsorption of either monomers, or polymer onto the PS-DVB surface, (iii) solvent induction of functional group orientation at the PS-DVB-polymer interface and polymer-water interface, (iv) a cross-linking reaction that forms a hydrophilic surface layer, and (v) derivatization of the surface layer with stationary phase.

Real-time kinetic analysis of limited proteolysis by ion-exchange chromatography using compressed, non-porous agarose beads

In biotechnology there is a great need for methods that can be used for kinetic studies of ongoing processes, such as limited proteolysis. Ion-exchange chromatography on a nonporous, compressed agarose matrix was used in the study presented in this paper to monitor papain cleavage of fungal cellulases. This non-porous matrix allows completion of a chromatographic analysis, with baseline resolution, within 30-60 s. Utilizing this very fast chromatographic method one can monitor a proteolysis 'continuously' by repeated chromatographic analysis of the incubation mixture and, if desired, terminate it at the optimal moment. Fractions were also collected for identification by activity assays and analytical SDS-PAGE.

Rapid separation, quantitation and purification of products of polymerase chain reaction by liquid chromatography

The polymerase chain reaction (PCR), a new, powerful method for rapid enzymatic amplification of specific DNA fragments, has gained tremendous popularity in molecular biology. This paper describes the successful application of liquid chromatography to the analysis of products of the PCR. Efficient separation of both DNA restriction fragments and amplified PCR products were achieved in 10-12 min on a new ion-exchange column, DEAE-NPR, packed with 2.5-microns non-porous particles. The PCR products were quantitated with a reproducibility within 10%. Use of liquid chromatography was demonstrated for separation and quantitation of PCR products in amounts below those required for direct analysis by ethidium bromide gel electrophoresis or a Hoechst 33258 dye-based fluorescence assay. Liquid chromatography was also demonstrated to be effective for quick optimization of PCR procedures.

Micropellicular stationary phases for rapid protein analysis by high-performance liquid chromatography

The high separating speed, efficiency and operational stability of various micropellicular stationary phases are demonstrated in the high-performance liquid chromatography (HPLC) of biopolymers. The micropellicular sorbents were prepared from 2-microns fluid-impervious silica microspheres as the support, with a thin layer of different retentive materials at the surface. These include a molecular fur of octyl or stearyl chains for reversed-phase chromatography as well as a hydrophilic layer with amino groups and polyethyleneglycol chains for anion-exchange and hydrophobic interaction chromatography, respectively. The use of appropriate micropellicular stationary phases for protein separation by metal-interaction and affinity chromatography is also illustrated. In most cases, operation at elevated column temperature was found to be preferable for rapid separations. Preliminary results show that the stability of micropellicular columns compares very favorably with that of columns conventionally used in HPLC and that they are easy to maintain.

Fast separation of biological macromolecules on non-porous, microparticulate columns

The use of high-performance liquid chromatographic columns for the separation of proteins and nucleic acids is gradually increasing in biochemical laboratories. The efficiency of these columns for such separations has been much lower than that achievable for the separation of smaller molecules. Non-porous microparticulate packings are the logical answer one arrives at after consideration of the chromatographic behaviour of proteins. Non-porous stationary phases are described for the separation of proteins, peptides and nucleic acids. The stationary phases used are TSK-Gel NPR-C18, TSK-Gel NPR-DEAE, TSK-Gel NPR-SP and HYTACH MicroPell C18. A number of fundamental properties of columns based on these sorbents were evaluated, such as permeability, retention behaviour towards small and large molecules, load capacity and stability. Instrumental requirements for these columns are discussed and some applications described.

Evaluation of advanced silica packings for the separation of biopolymers by high-performance liquid chromatography. VI. Design, chromatographic performance and application of non-porous silica-based anion exchangers

The linear solvent strength model of Snyder was applied to describe fast protein separations on 2.1-micron non-porous, silica-based strong anion exchangers. It was demonstrated on short columns packed with these anion exchangers that (i) a substantially higher resolution of proteins and nucleotides was obtained at gradient times of less than 5 min than on porous anion exchangers; (ii) the low external surface area of the non-porous anion exchanger is not a critical parameter in analytical separations and (iii) microgram-amounts of enzymes of high purity and full biological activity were isolated.

High-performance liquid chromatography of proteins on N-methylpyridinium polymer columns

Two types of 4-methylpyridinium polymers (4VP-DVB-Me and 4VP-EG-Me, cross-linked with divinylbenzene and ethylene glycol dimethacrylate, respectively) were employed for the analysis of proteins in ion-exchange high-performance liquid chromatography. These polymers had different physical properties in the dry state, but showed similar retentions in size-exclusion chromatography using carbohydrate standards. Generally, the 4VP-EG-Me column was superior to the 4VP-DVB-Me column with regard to separation and recovery of proteins.

High-performance anion-exchange chromatography of proteins using aza-ether bonded silica-based phases

The use of wide-pore silica-based hydrophilic aza-ether bonded phases for the chromatographic separation of proteins under anion-exchange conditions was studied. Polyether silanes containing terminal morpholine or piperazine derivatives are synthesized for attachment to the silica surface and provide a flexible approach to bonded phase design. In one instance, a quaternized amine support may be prepared by further derivatization of the methylpiperazine bonded phase. The supports provide high-performance anion-exchange chromatographic separations of proteins using gradients of increasing salt content, e.g., to 1.0 M sodium acetate at pH 7.0. The salt type and concentration can be varied to control protein retention while the buffer system used at pH 7.0 exerts a minimal influence on the separation. The anion exchangers may be reproducibly prepared and exhibit chromatographic retention stability at pH 7.5 for at least 2 months of operation. Acceptable capacity for protein on the bonded phase is demonstrated with high recovery of solute mass. The flexibility in anion exchanger design provides a probe of bonded ligand hydrophobic effects which can contribute in an undefined and deleterious manner to the desired ion-exchange separation. Taken together, these results provide a greater insight into the operating characteristics of anion exchangers, especially with regard to competing retention mechanisms.

Micropreparative high-performance liquid chromatography of proteins and peptides

The use of short microbore reversed phase and ion-exchange HPLC columns in the preparation of low level (submicrogram) quantities of proteins and peptides is discussed. The sequential use of columns of differing selectivity to purify complex mixtures is described. An example is given of the use of microbore columns to purify a murine myeloid leukemia inhibitory factor prior to sequence analysis.

Rapid high-performance affinity chromatography on micropellicular sorbents

Short columns (30 x 4.6 mm I.D.), packed with 2-micron fluid-impervious silica microspheres with surface-bound Protein A or a lectin were used for fast separation and quantitation of immunoglobulins and glycoproteins by biospecific interaction chromatography. With stepwise elution, the total analysis time including column reequilibration did not exceed 3 min. In the assay of IgG with a stepwise change in pH best results were obtained with citrate buffer, which facilitated not only fast but also very sensitive analysis. The calibration curve was linear in the range 0.5-40 micrograms of human IgG. By using morpholinoethanesulfonic acid-4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid-acetic acid buffer with a linear decrease in pH from 6.0 to 4.0 and an increase in magnesium chloride concentration to 200 mM for elution, the subclasses of human IgG were separated at 40 degrees C above pH 4.0 in 3 min. Micropellicular concanavalin A and wheat germ agglutinin were used for rapid affinity chromatography of horseradish peroxidase and fetuin, respectively. The results suggest that micropellicular affinity sorbents afford fast and sensitive high-performance liquid chromatographic analysis by biospecific interaction chromatography. Although developed primarily for rapid analysis, the micropellicular Protein A exhibited unexpectedly high adsorption capacity (e.g., 4.5 mg human IgG per ml of wet bed volume). This suggests that such columns could be employed in preparative protein chromatography as well.

High-performance liquid chromatography of proteins on compressed, non-porous agarose beads. II. Anion-exchange chromatography

Macroporous agarose beads were rendered impermeable to proteins by shrinkage and cross-linking in organic solvents. The chromatographic properties of compressed beds of these non-porous beads derivatized for high-performance ion-exchange chromatography were studied, e.g., the resolution as a function of gradient time, flow-rate (at constant gradient volume) and loading capacity. The columns permit high flow-rates and the resolution is about the same at low and high flow-rates. The beads are stable up to pH 14.

High-performance liquid chromatography of proteins on compressed, non-porous agarose beads. I. Hydrophobic-interaction chromatography

Macroporous agarose beads were converted into non-porous beads by shrinkage and cross-linking in organic solvents. These beads could be used for high-performance hydrophobic-interaction chromatography without derivatization with non-polar ligands, because the 1,4-butanediol diglycidyl ether, used as cross-linker, gives relatively hydrophobic bridges. The resolution for compressed columns packed with these beads was determined as a function of gradient time at constant flow-rate, flow-rate at constant gradient volume and flow-rate at constant gradient time and as a function of loading capacity. Interestingly, the resolution is virtually independent of flow-rate at constant gradient volume even when the column is packed with relatively large beads (diameter 30 microns). The beads have the advantage of being stable up to pH 14.

Rapid analysis of proteins and peptides by reversed-phase chromatography with polymeric micropellicular sorbents

Peptides and proteins were separated by reversed-phase chromatography on a 30 x 4.6 mm I.D. column packed with non-porous crosslinked polystyrene particles having a mean particle diameter of 3 micron and a rugulose surface. The polymeric support did swell slightly in organic solvents, but the estimated 5-8% change in particle diameter did not adversely affect the efficiency of the column which was used repeatedly with gradient elution from water to organic solvent under conditions typically employed in reversed-phase chromatography. In these experiments, the pH of the eluent was varied in a wide range in order to compare the effect of acidic and alkaline eluents on the separation of protein and complex peptide mixtures. The column showed no deterioration even after extensive exposure to alkaline mobile phases. The retention behavior of sixteen proteins having widely different pI values was studied as a function of the eluent pH. The chromatographic system exhibited large selectivity differences upon changing the pH of the eluent from 2 to 11. Analytical information about peptide and protein mixtures could therefore be enhanced by using eluents at the pH extremes. At the pH extremes of 2 and 11 peak sharpness and protein mass recovery were found to be superior to those obtained with neutral eluents. Usually the column temperature was held at 80 degrees C and typical analysis times ranged from 30 s to 10 min as illustrated by chromatograms of protein mixtures and by peptide maps. With regular use under such conditions the column showed no deterioration after three months.

Synthesis of a non-porous, polystyrene-based strong anion-exchange packing material and its application to fast high-performance liquid chromatography of proteins

Adsorbed coating technology has been used to produce a strong anion-exchange stationary phase on 3-micron non-porous poly(styrene-divinylbenzene) particles. In order to take full advantage of the excellent kinetic properties of the resultant packing material, small columns of 5 mm X 6 mm I.D. were used. These columns were pressure- and pH-stable and allowed protein separations to be made in less than 1 min at ambient temperature.

Ion-exchange chromatography of proteins on a polyethyleneimine-grafted hydrophilic polymer for high-performance liquid chromatography

A new, macroporous, synthetic polymer, Hydrophase HP-PEI, having highly hydrophilic surface characteristics enhanced by evenly distributed polyethyleneimine groups on its surface, was evaluated as an high-performance ion-exchange chromatographic packing material for the separation of proteins and nucleotides. A steel column (100 mm x 7.8 mm I.D.) packed with this material produces more than 33,000 plates per m. This base polymer included large proteins, such as thyroglobulin and apoferritin, in a size-exclusion mode. With various proteins it gave high recovery, high resolution and high capacity.

Rapid peptide mapping by high-performance liquid chromatography

Short columns, packed with pellicular sorbents made of 2-micron fluid-impervious silica microspheres, were used at elevated column temperatures for rapid peptide mapping by high-performance liquid chromatography (HPLC). Enzymic digests of various proteins were chromatographed by gradient elution. In many cases the time of analysis was 10 min or less. In order to increase the retention particularly, that of short, polar peptides under such conditions, 1 mM octyl sodium sulfate or 5 mM hexyl sodium sulfate were added to the starting eluent. The length of the 4.6 mm I.D. columns was 30 or 75 mm, the sample load was in the range of 10-1000 pmoles. Highest analytical sensitivity was obtained at a flow-rate of 0.5 ml/min and room temperature, whereas for rapid analysis flow-rates of up to 2 ml/min were used at 80 degrees C. This temperature allowed the use of relatively high flow velocities of the mobile phase without significant loss in efficiency. The method was highly reproducible, as shown by the results obtained by automated analysis of cyanogen bromide fragments of lysozyme at high speed. The quality of the rapid peptide maps compares favorably with that of maps obtained by standard reversed-phase HPLC methods, which require much longer analysis times.

Carrier-free zone electrophoresis, displacement electrophoresis and isoelectric focusing in a high-performance electrophoresis apparatus

A characteristic feature of high-performance electrophoresis (HPE), the electrophoretic counterpart of high-performance liquid chromatography (HPLC), is that the separation chamber is a thin-walled, narrow-bore (0.05-0.3 mm) glass or fused-silica capillary tube for rapid dissipation of the Joule heat in order to minimize thermal zone deformation even at high field strengths. This paper is centered around the usefulness of HPE for separation in a carrier-free medium (i.e., in buffer alone) and deals with both zone electrophoresis, isoelectric focusing and displacement electrophoresis. Examples are given of analytical and micropreparative separations of inorganic and organic ions, proteins, viruses and bacteria. The run times are 5-30 min. Discontinuous buffer systems have up to now been used exclusively for the separation of proteins by electrophoresis in polyacrylamide gels ("disc electrophoresis"). However, the Ornstein and Davis discontinuous buffer system has been modified to adapt it to carrier-free zone electrophoresis in order to achieve automatic sharpening of the starting zone. Very high resolution of serum proteins was obtained when they were subjected to free high-performance disc electrophoresis in such a modified buffer system. To show that the HPE apparatus permits electrophoresis also in a gel medium, a polyacrylamide electrophoresis in SDS is presented. This experiment illustrates the difference between electropherograms obtained in free solution and in a molecular-sieving medium. Detection can be performed both on- and off-tube. The latter technique permits the rapid identification of the solutes by photodiode array spectrophotometry and the collection of fractions for further studies. The former detection method is simpler but mainly useful for analytical purposes. Non-UV-absorbing ions can be monitored with the aid of an on-tube UV detector if the run is performed in a UV-absorbing buffer.

Performance evaluation of non-porous versus porous ion-exchange packings in the separation of proteins by high-performance liquid chromatography

The performance of a non-porous, anion-exchange packing was evaluated and compared with a number of similar porous high-performance liquid chromatography packings. The non-porous columns were found to be equally efficient for proteins spanning a wide range of molecular weights, while the porous columns exhibited decreasing efficiency as the proteins became larger. The porous materials also exhibited size exclusion effects that were not seen with the non-porous materials, which partially accounts for the loss of efficiency with large proteins. When increasingly steep gradients were employed, the loss of resolution was less with the non-porous materials.

Ion-exchange and hydrophobic-interaction high-performance liquid chromatography of proteins. A practical study

A number of commercially available columns for ion-exchange and hydrophobic-interaction high-performance liquid chromatography (HPLC) have been tested, ranging from very fast columns with low capacity to preparative columns. The experiments represent a selection of column applications likely to occur in a biochemical laboratory. The use of several ion-exchange columns for separation of serum and membrane proteins has been demonstrated. Columns with a silica gel matrix and with a polymer matrix have proved to be of equal value in experiments with water-soluble proteins. In experiments with hydrophobic membrane proteins the choice of the column depends on the protein to be isolated. A combination of a cation-exchange and an anion-exchange column as a tandem as well as a mixed-bed column, were applied for the separation of serum proteins and for the isolation of a 175,000-dalton membrane glycoprotein. One problem of hydrophobic-interaction HPLC is the poor solubility of some proteins, for example serum proteins at high salt concentrations. This difficulty can be overcome by the use of columns with higher hydrophobicity which require lower initial salt concentrations. Less hydrophobic columns have been shown to separate hydrophobic membrane proteins by a combination of salt and detergent gradients.

Rapid cation-exchange chromatography of hemoglobins and other proteins

A new, weak cation exchanger (MA7C) is useful for the very rapid resolution of protein mixtures. MA7C columns (30 X 4.6 mm I.D.) are packed with non-porous spherical particles (7-micron in diameter) having carboxylic acid ion-exchange groups. These columns can readily separate human hemoglobin A1c from other hemoglobin species in 7 min. Quantitative results agree well with those of accepted techniques. Other separations are possible with flow-rates up to 5 ml/min. Chromatography on MA7C columns is characterized by very narrow bandwidths, even at high flow-rates.