Analytical Methods and Bench Scale Preparative Bioseparations

The development of efficient and reliable processes for bioseparations is dependent on the availability of suitable analytical methods. This means it is important that work on analytical methodology for the bioproduct of interest starts at the very beginning of process development. Analytical studies are important throughout the development and scale up of the process, as changes can occur either to the product or to its associated impurities from what may be thought of as minor changes in the process. This chapter gives access to the vocabulary and techniques used in quality control and analytical development activities, starting with a description of specifications typically set for a pharmaceutical and the rationale behind them. Then, before discussing the assays themselves, we describe assay attributes, which can be measured and used to help not only the assay developer but also the biochemist and engineer responsible for developing downstream processes determine the usefulness and meaning of the assay. Finally, we turn to assays that are commonly applied in biotechnology, as they apply to biological activity, identity, and purity. These assays are the ultimate yardsticks by which the process is measured. Purification methods are developed for their ability to remove a contaminant from the product of interest, whether it is a related molecule, a contaminant related to a host organism, such as DNA or endotoxin, or a process contaminant, such as a residual solvent or water. Critical to understanding process performance is an understanding of how the assays that measure these contaminants have been developed, what the assay strengths and limitations are, and what they indicate and why. Electrophoresis and magnetic separation are two methods that are now used for the bench scale preparative purification of bioproducts, including living cells. The electrophoresis systems with the highest capacity are free-flow electrophoresis, density gradient electrophoresis, recycling free-flow isoelectric focusing, and rotating isoelectric focusing, and the principles of operation of these are discussed. The physical principles of magnetic separations are presented, as well as magnetic reagents and applications of magnetic separators.