Column Technology

In order to get efficient columns of large diameter (i.e.

>5 cm) for preparative purposes, it is necessary to have a packing material of adequate quality and also the appropriate column technology. Column technology is a very critical issue, since it is known that above a certain diameter columns tend to be unstable because of bed settling and the resulting formation of voids in the packing. These voids are very detrimental to the column efficiency and are responsible for band distortion. In addition, large columns are potentially more difficult to pack than small ones, particularly when small particles (<50 |im) are used. Indeed, the high pressure slurry-packing technique used to pack

Figure 2

Figure 3 Methods of dynamic compression. (A) Radial compression; (B) axial compression.

analytical columns cannot be used for large diameter columns for both practical and technical reasons.

Various solutions have been proposed to solve the problem of bed stability. It seems that the best approach is to compress the bed of particles, either radially (using columns with flexible walls immersed in a pressurized fluid) or, preferably, axially using a piston (see Figure 3). This bed compression must be dynamic so that voids are eliminated as soon as they form. Using dynamic axial compression, it is possible to pack columns of large diameter with small particles offering the same efficiency as analytical columns (see Figure 4). This technology is particularly versatile because it gives the operator the possibility of packing the column very easily and quickly with

Figure 4 Comparison of chromatograms from (A) 25 cm x 4.6 mm and (B) 25 cm x 150 mm.

columns.

Figure 4 Comparison of chromatograms from (A) 25 cm x 4.6 mm and (B) 25 cm x 150 mm.

columns.

any type of material. This is clearly important for equipment used in production where downtime has to be minimized. In addition, the length of the bed can be easily adjusted to optimize the column efficiency. Finally, whatever the compression technique used, it is very important to design the column ends properly. Indeed, in order to generate piston flow and avoid band distortion due to unequal flow distribution, it is necessary to spread the flow of liquid evenly across the cross-section of the column.

Solar Panel Basics

Solar Panel Basics

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