Rotating unit for preparative-scale gas chromatography

Continuous matrix assisted refolding of alpha-lactalbumin by ion exchange chromatography with recycling of aggregates combined with ultradiafiltration

Continuous matrix assisted refolding (MAR) can be achieved on a solid support by using a continuous chromatographic system. Recycling the aggregate fraction, simultaneously formed during a refolding reaction, can further increase the refolding yield. Due to the nature of this reaction, aggregates are the main reason for a refolding yield below stoichiometric conversion. A preparative continuous annular chromatographic system (P-CAC) equipped with an ion exchange resin was used to continuously refold the model protein alpha-lactalbumin. For this purpose, this protein was denatured, reduced and adsorbed on the ion exchange resin. Elution was performed with or without redox reagents in the buffer system permitting fast formation of the native disulfide bonds. In the case redox reagents were present, the protein refolds then during its residence time on the matrix. However, aggregate formation is also increased and refolding yields are lower. Tightly bound aggregates were removed from the column by 2M guanidinium hydrochloride. In order to increase the system yield, this aggregate fraction was recycled after lowering the conductivity by ultradiafiltration and adjustment of the protein concentration by dilution. For on-column refolding, recycling of aggregates at a recycling rate of 0.17 increased the system yield from 25% to 30%. An algorithm was developed to show interdependencies of the single influencing parameters. The operability of the system was demonstrated but limitations due to instability of the P-CAC, especially inhomogeneous flow and peak wobbling, have to be considered.

Continuous annular chromatography

The principle of continuous annular chromatography (CAC) has been known for several decades. CAC is a continuous chromatographic mode, which lends itself to the separation of multi-component mixtures as well as of bi-component ones. In CAC, the mobile and stationary phases move in a crosscurrent fashion, which allows transformation of the typical one-dimensional batch column separation into a continuous two-dimensional one. With the exception of linear gradient elution, all chromatographic modes have at present been applied in CAC. This review focuses on the capacity of CAC for preparative bioseparation. The historical developments and the predecessors of modern CAC are briefly summarized. The state-of-the-art in the theoretical prediction and simulation of CAC separations is discussed, followed by an overview of current CAC instrumentation and example applications, especially for the isolation of proteins and other bio(macro)molecules. In this context, issues of scale up as well as method development and transfer from batch to continuous CAC columns are discussed using recent bioseparation efforts as pertinent examples.

Improved performance of protein separation by continuous annular chromatography in the size-exclusion mode

In size-exclusion chromatography (SEC), proteins and peptides are separated according to their molecular size in solution. SEC is especially useful as an effective fractionation step to separate a vast amount of impurities from the components of interest and/or as final step for the separation of purified proteins from their aggregates, in a so-called polishing step. However, the throughput in SEC is low compared to other chromatographic processes as good resolution can be achieved only with a limited feed volume (i.e., maximal approximately 5% of the column volume can be loaded). This limitation opposed widespread application of conventional SEC in industry despite its excellent separation potential. Therefore a continuous separation process (namely preparative continuous annular chromatography) was developed and compared to a conventional SEC system both using Superdex 200 prep grade as sorbent. An immunoglobulin G sample with a high content of aggregates was chosen as a model protein solution. The influence of the feed flow-rate, eluent flow-rate and rotation rate on the separation efficiency was investigated. The height equivalent to a theoretical plate was lower for preparative continuous annular chromatography which could be explained by reduced extra column band broadening. The packing quality was proved to be identical for both systems. The productivity of conventional batch SEC was lower compared to continuous SEC, consequently buffer consumption was higher in batch mode.

Isolation of a recombinant antibody from cell culture supernatant: continuous annular versus batch and expanded-bed chromatography

Annular chromatography represents a crossflow approach to chromatographic separations, that allows the continuous separation of multicomponent mixtures. The potential of the method for continuous bioseparation has been discussed for some time, however, we demonstrate for the first time the processing of a complex feed (cell culture supernatant) taken from an actual (bio)process. Moreover, while previously published applications of annular chromatography concentrated on noninteractive (gel filtration) or nonspecific (ion exchange) chromatography, we show the possibility of continuous annular affinity chromatography. In particular, a commercially available preparative continuous annular chromatography (P-CAC) system was used to purify a recombinant antibody (human IgG(1)-kappa) from CHO cell culture supernatants by (pseudo)affinity chromatography on hydroxyapatite (HA) and rProtein A. Methods developed using small (2 mL) batch columns could be directly transferred to the P-CAC, where they yielded similar results in terms of final product quality. Yields were between 87% and 92% in the case of HA and between 77% and 82% in the case of rProtein A chromatography. DNA removal was nearly quantitative in all cases. Concomitantly, the antibody fraction of the total protein content was raised by one order of magnitude in HA and by a factor of 50 by rProtein A chromatography. In addition, a novel HA material (particle diameter -120 microm) was investigated, which was compatible with expanded-bed applications. However, the final purity of the antibody thus obtained and also the yields (<70%) were less than satisfactory.