Axial-compression technology

Column packing - dynamic axial compression technology... 

T ay, the major manufacturers routinely produce in the order of 100,000 columns per year, and experienced manufacturers have learned to pack columns to a high reproducibility of their performance and stability. Thus the technologies designed to avoid or eliminate column voiding are not needed any more and are found only in niches where the problems have not yet been solved. The primary example is preparative chromatography with large-diameter columns. Because of their importance in preparative HPLC, we will discuss here the principles of radial- and axial-compression technologies. 

It is now well accepted that, for liquid chromatography, the obtention of large diameter, very efficient and stable columns requires the dynamic axial compression technology. The similarity between the HPLC and SFC columns and stationary phases suggest that the dynamic axial compression is the good solution and indeed efficiencies of 63 000 plates per meter were obtained with a good stationary phase. 

Correct column packing is obtained by using preparative columns equipped with dynamic axial compression (DAC) technology [10, 11]. The column includes a movable piston attached to a hydraulic jack. The piston is used to pack and unpack the column and to maintain the stationary phase under dynamic compression, ensuring perfect particle stacking (Figure 12.5) and bed stability through time. 

Electrically or hydraulically moved piston In terms of column technology, there is a consensus today that the best (and probably only) feasible approach at any size is dynamic axial compression (DAC). The piston can be driven by a hydraulic jacket, or pushed by a liquid, by a spring, or by an electrical motor. Radial compression is an alternative but it does not seem to be available at (very) large column diameter sizes. It also requires the use of prepacked cartridges, thus reducing the operator s freedom compared to DAC. Under appropriate conditions, the DAC technology ensures bed stability and reproducible performance. DAC can be scaled-up to very large size with remarkable reproducibility in performance. This has been verifled with columns up to 1600 mm internal diameter. 

Packing technology Dynamic axial compression Vacuum packing Circle suspension flow packing... 

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