Preparative Chromatography - Alternative Preparative Techniques > Page 44

Alternative Preparative Techniques

Although there may well be an economic limit to the scale of preparative chromatography, there does not appear to be any practical constraint to column size. Performance data from columns of over a meter in diameter have been reported which has shown that they can be operated very successfully. Unfortunately there is very limited design and operational data available for such columns due to the highly proprietary nature of their use. Large diameter columns, however, must have an appropriate sample distribution system at the column inlet. This is to ensure that the sample is dispersed evenly over the whole cross section of the column so that the full capacity of the column is utilized and as a secondary consideration significant column efficiency is not lost. Although the actual column may need to be custom made, solvent pumps, with high volume delivery at moderate pressures, are readily available. Most of the pipe fittings, valves, etc. can be obtained from manufacturers that supply equipment for general chemical plant operation. Large columns, handling large sample loads, will be effected by the heat generated in the column during solute absorption in the stationary phase. Consequently, it may require appropriate heat exchange systems to be arranged to prevent the separation being denigrated by localized temperature changes.

A number of alternative LC distributions systems (distribution systems, that is, other than simple columns) have been developed for preparative work and need to be described. Some of these have found limited use but, nevertheless, have been shown to be very effective for large scale chromatographic purification for certain types of application. Unfortunately, the successful applications of these systems are also largely proprietary and so operating details are often not easy to obtain.