General strategies in the separation of proteins by high-performance liquid chromatographic methods

High temperature fast chromatography of proteins using a silica-based stationary phase with greatly enhanced low pH stability

Reversed-phase liquid chromatography (RPLC) is very widely used for the separation and characterization of proteins and peptides. A novel type of highly stable silica-based stationary phase has been developed for protein separations. A dense monolayer of dimethyl-(chloromethyl)phenylethyl)-chlorosilane (DM-CMPES) on the surface of silica is "hyper-crosslinked" with a polyfunctional aromatic crosslinker through Friedel-Crafts chemistry resulting in stationary phases with extraordinary stability in acidic media. Elemental analysis data confirm the high degree of cross-linking among the surface groups. The hyper-crosslinked phases are extremely stable under highly acidic mobile phase conditions even at a temperature as high as 150 degrees C. A wide-pore (300 A) material made in this way is used here to separate proteins by a reversed-phase mechanism and compared to a commercially available "sterically protected" C18 phase. For small molecules, including neutral and basic compounds, these crosslinked phases give comparable peak shape and efficiency to the commercial phase. Our results show that no pore blockage takes place as commonly afflicts polymer coated phases. In consequence, protein separations on the new phases are acceptable. Using strong ion-pairing reagents, such as HPF6, improves the separation efficiency. Compared to the commercial phases, these new phases can be used at lower pHs and much higher temperatures thereby enabling much faster separations which is the primary focus of this work. Better efficiency for proteins was obtained at high temperature. However, at conventional linear velocities the instability of proteins at high temperature becomes a problem which establishes an upper temperature limit. Uses of a narrowbore column and high flow rates both solves this problem by reducing the time that proteins spend on the hot column and, of course, speeds up the separation of the protein mixture. Finally, an ultrafast gradient (<1 min) protein separation was obtained by utilizing the high temperature and thus high linear velocities afforded by the extreme stability of these new phases. The phases are stable even after 50h of exposure to 0.1% TFA at 120 degrees C. This paper is dedicated to the memory of Csaba Horvath whose work in high temperature HPLC inspired the development of the stationary phases described here.

Parametric investigation on the effect of channel topologies on electrophoretic separations

This paper presents a systematic study that illustrates the importance of the topologies of microchannels on electrokinetically based separation. Using theoretical and numerical analyses, we designed and showed that topologies that significantly increased the surface-to-volume ratio of the channel can provide dramatic improvement in the ability of the channel both to dissipate the heat generated by Joule heating and to reduce the axial dispersion associated with the siphoning effect. The incremental benefit and tradeoff of geometric complexity was also evaluated. The improvement offered by topographically patterned channels, such as finned structures, is especially pertinent in the development of preparative or semi-preparative scale electrokinetically driven separations, such as capillary electrophoresis and capillary electrochromatography, in which large cross sections of channels are required to achieve the needed volumetric throughput.

Multiple ligand applications in high-performance immunoaffinity chromatography

A mixture of antibodies specific for albumin and transferrin, immobilized onto a single support, was used for the simultaneous extraction of albumin and transferrin from immunoglobulin G by high-performance immunoaffinity chromatography. The affinity column was coupled to a strong cation exchanger in order to monitor the success of the extraction and to demonstrate the compatibility of the two chromatographic modes. Coupling of non-affinity chromatography with multiple ligand affinity chromatography is discussed as an alternative to positive affinity chromatography for protein purification.

Rapid, two-step purification process for the preparation of pyrogen-free murine immunoglobulin G1 monoclonal antibodies

A cost-efficient process was specifically designed for the preparation of gram amounts of highly pure murine immunoglobulin (Ig) G1 monoclonal antibodies (mAbs). This rapid, simple and scalable purification process employs a unique binding and elution protocol for IgG1 mAbs on a silica-based, mixed-mode ion-exchange resin followed by conventional anion-exchange chromatography. mAbs are bound to BakerBond ABx medium at pH 5.6 directly from serum-supplemented hybridoma culture supernatants. Contaminating proteins and nucleic acids are removed by an intermediate wash at pH'6.5, followed by the specific elution of IgG1 mAbs with 100 mM Tris-HCl (pH 8.5). The mAb eluate is then loaded directly on to QAE-Sepharose Fast Flow medium and eluted with 10 mM sodium phosphate buffer (pH 7.4), containing 150 mM sodium chloride. The resulting IgG1 mAbs are greater than 98% pure, free from measurable endotoxin, formulated in a physiological buffer and suitable for in vivo applications.

Recent advances in capillary electrophoresis of proteins, peptides and amino acids

The current status of high-performance capillary electrophoresis as an analytical separation method for proteins, peptides and amino acids is assessed. Recent advances in suppressing the effects of electroosmotic flow and irreversible adsorption of proteins at the capillary wall are reviewed, together with procedures for optimal separations of peptides and amino acids. The detection aspects emphasize the role of laser-induced fluorescence and capillary electrophoresis/mass spectrometry in high-sensitivity measurements.

Protein purification

This monograph summarizes recent developments in the purification and analysis of natural and recombinant proteins. The basic strategies employed in protein purification are reviewed with regards to the characteristics of the protein of interest that may aid its isolation, choice of the starting material, and use of denaturants. Preparation of cell-free extracts followed by bulk precipitation and/or phase partition constitute the initial steps of many purification schemes. Chromatographic methods (size exclusion, ion exchange, hydroxylapatite, reversed phase, hydrophobic interaction and affinity based) utilizing either traditional, low pressure or high-performance liquid chromatography instrumentation are discussed. Electrophoretic techniques used to analyze the homogeneity of the protein product include SDS-PAGE, isotachophoresis, IEF and two dimensional gel electrophoresis.

Comparison of mono Q, superose-6, and ABx fast protein liquid chromatography for the purification of IgM monoclonal antibodies

Nine immunoglobulin M (IgM) monoclonal antibodies (MAbs) produced in ascites fluids or in cell culture supernatants, have been purified on a fast protein liquid chromatography (FPLC) system using anion-exchange, size-exclusion, or mixed-mode chromatography matrices. The use of a mixed-mode ABx column provided an IgM that had a purity of greater than 99% after a single purification step. Anion-exchange chromatography using a Mono Q column, provided a partial purification of the IgM which could subsequently be purified to a product of ca. 90% purity (determined from sodium dodecyl sulfate polyacrylamide gel electrophoresis) by size-exclusion chromatography on a Superose-6 column. Alternatively, the ascites containing the IgM was ammonium sulfate precipitated and chromatographed on the Superose-6 column under normal- as well as high-ionic strength conditions, which also yielded a product of ca. 90% purity. The purification of IgM from concentrated cell culture supernatants was evaluated using the Superose-6 or the ABx column. IgM purified from this source was greater than 99% pure when chromatographed on the mixed-mode column and ca. 60% pure on the size-exclusion column. MAbs from each of the procedures retained their immunoreactivity, as shown by indirect immunofluorescence staining of fixed cell preparations. A comparison of these methods revealed that mixed mode chromatography was simple, efficient, and yielded a product of high purity. The optimization of these methods facilitates the large-scale purification of mouse IgM MAbs and provides practical procedures for generating IgMs for use as diagnostic and therapeutic reagents.

Separation of proteins by reversed-phase high-performance liquid chromatography. I. Optimizing the column

In the process of developing a new analytical technology (the chromatophoresis process) which couples reversed-phase high-performance liquid chromatography (HPLC) to sodium dodecyl sulfate polyacrylamide gel electrophoresis in a real-time automated system, it was apparent that improvements in resolving power for the first-dimension (HPLC) separation were necessary. The present paper describes the optimization of the column for our initial work on reversed-phase HPLC separations. Polymeric (polystyrene) packings having particle diameters of 5 micron and pore diameters of 300 A were generally superior in terms of resolution, sample recovery and minimization of "ghosting". Optimum column dimensions were 50 x 1.0 mm I.D. for the flow-rates required in our system (10-100 microliter/min).