Holwill, Ian Leslie John; (1993) Optical measurement and signal evaluation relating to particulate properties during purification of biological suspensions. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The variable nature of conditions in downstream processing operations in biotechnological and other areas necessitates the on-line monitoring of process variables for rapid analysis and possibly subsequent control to optimise yield in a multi-stage purification process. Optical measurement of such parameters offers a fast and non-invasive method to interrogate the process with the added advantage of the possibility to construct a robust, miniaturised measurement system using modern optical components. The problems encountered are turbulent and turbid conditions which are usually unsuitable for light scattering measurements. Also access to the process stream is often not simple and a method of automatic sampling must be employed. This thesis describes the application of dynamic light scattering to downstream processing operations and particularly to the measurement of virus-like particles and separation from their yeast host. The construction of a miniaturised dynamic light scattering system is also described. Several data analysis methods are assessed with a view to using them in a rapid analysis configuration. Most of the methods require moderate processing power but consideration is given to extensions to the standard techniques to apply them in a parallel processing environment which today is on the increase. The improvement of the convergence of such routines is discussed with the addition of prior information. A particular area of interest is the rapid sample preparation required before analysis by light scattering to improve the data quality. Large particulate material is usually not tolerated well in this method of measurement and should be removed. A technique is described and tested which facilitates rapid in-situ sample preparation and optical analysis. Otherwise sample preparation is carried out prior to analysis. As well as a dynamic light scattering study, an overview of optical measurement by other means in yeast-based systems is discussed with a view to optimising the system configuration.

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