The Use of Alternative Modes and Techniques in Process Situations

The effect of loading beyond the point at which bands touch will differ from separation to separation. We must differentiate between a mass overload and a volume 

There is one major problem associated with working at very high loading which is the determination of cut points. Ultraviolet detectors become overloaded at relatively low concentrations and, whilst refractive index detectors are better in this respect, they suffer from other disadvantages such as an inability to cope with solvent gradients. Split flow to the detector may be helpful, but can cause problems. Where displacement is taking place, the boundary between adjacent peaks can be very sharp, and if the materieils are closely related, may not show on a detector suffi- 

Unfortunately, there is no simple answer to the problem of developing a separation for process use, and there is no substitute for experimentation. What is important, is that we should be aware of the wide range of options which are open to us, and not be blinkered by experience gained in analytical and small-scale preparative work. Process chromatography is a subject in its own right, with its own problems, not simply an extension of other forms of chromatography. 

There are two main application areas for size exclusion chromatography of proteins desalting or group separation and fractionation. Both areas are industrially of equal importance but the prerequisites for their ability of being sealed-up are quite different 

The principle of fractionation by SEC, ie, the total separation of two or more proteins that differ sufficiently in size and/or shape, is in the majority of cases based on all the components diffusing into the interior of the particle gel matrix. With few exceptions, fractionation SEC is therefore a process with comparatively low productivity due to the low gel diffusivity of proteins, the requirement of long columns, low flow-rates and, for optimum resolution, small sample volumes (0.005 - 0.05 V ). In many industrial applications, scaling-up of fractionation SEC means stacking several short, large diameter columns connected by small bore tubing. 

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