Product analysis - Pharmaceutical Biotechnology: Concepts and Aapplications - page 184

the presence of carbohydrates). Glycoproteins varying slightly in their carbohydrate content will
vary in their sialic acid content and, hence, exhibit slightly different pI values. In such instances,
isoelectric focusing analysis seeks to establish batch-to-batch consistency in terms of the banding
pattern observed.
Isoelectric focusing also fi nds application in analysing the stability of biopharmaceuticals over
the course of their shelf life. Repeat analysis of samples over time will detect deamidation or other
degradative processes that alter protein charge characteristics.
7.4.1 Capillaryelectrophoresis
Capillary electrophoresis systems are also likely to play an increasingly prominent analytical role
in the QC laboratory (Figure 7.2). As with other forms of electrophoresis, separation is based upon
different rates of protein migration upon application of an electric fi eld.
As its name suggests, in the case of capillary electrophoresis, this separation occurs within a
capillary tube. Typically, the capillary will have a diameter of 20-50 µm and be up to a 1 m long
(it is normally coiled to facilitate ease of use and storage). The dimensions of this system yield
greatly increased surface area:volume ratio (compared with slab gels), hence greatly increasing
the effi ciency of heat dissipation from the system. This, in turn, allows operation at a higher
current density, thus speeding up the rate of migration through the capillary. Sample analysis
can be undertaken in 15-30 min, and on-line detection at the end of the column allows automatic
detection and quantifi cation of eluting bands.
The speed, sensitivity, high degree of automation and ability to quantitate protein bands directly
render this system ideal for biopharmaceutical analysis.
Figure 7.2 Photograph of a capillary electrophoresis system (the HP-3D capillary electrophoresis system
manufactured by Hewlett Packard). Refer to text for details. Photograph courtesy of Hewlett Packard GmbH,
Germany