Radial compression technology

Radial compression uses radial pressure applied to a flexible-wall column to lessen wall effects. The mobile phase has a tendency to flow slightly faster near the wall of the column because of decreased permeability. The solute molecules that happen to be near the wall are carried along faster than the average of the solute band, and, consequently, band spreading results. Preparative scale radial compression chromatography columns have been found to possess efficiencies close to those of analytical-scale columns when an adequate radial compression level is used. Radial compression technology also helps lower the cost by substituting reusable column holders in place of expensive steel columns. 

One can get that better resolution for a particular particle size without the increased pressure through radial compression technology. The need to improve resolution as in the analytical world is there, but in the preparative world there is also the need to control the bed structure over long periods of time. The use of massive overload and massive overworking of the column to serve production purposes, demands a more rigid control over the... 

Radial-compression technology, 66-70 Random-walk theory, 24 Recycling, 267-268 Reduced parameters. 15... 

Radial compression technology was developed by workers at Waters as an alternative to classic column technology (10,11). Two weaknesses of classic column technology were addressed by radial compression technology ... 

In radial compression technology, the packed bed is contained in a flexible-wall tubing. Controlled hydraulic or mechanical forces are applied umformly to the outside wall of the column (Fig. 3.11). This compresses the packed bed, resulting in a denser and—when applied properly—more uniform structure. The technology is derived from isostatic compaction, which is frequently used in the ceramics industry, for example, in the mass production of spark plugs. 

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. 

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. 

The interstitial fraction of an uncompressed bed of hard spherical particles packed by conventional packing technologies is 40 2%. When hydraulic radial compression is applied to such a bed, it readily densities until an interstitial fraction of 34 1% is obtained at 3 MPa. A further increase in... 

Recent technological advances in the last two decades have led to the development of self-expanding or expandable metallic mesh stents. These stents represent the latest technology for the treatment of malignant and benign airway obstructions. A stent can be described as a tubular prosthesis that maintains luminal patency and a predefined luminal diameter of a tubular structure by opposing radial forces to extrinsic or intramural compressive forces. Thus, a stent provides internal support for luminal patency. 

Wood. H. J, Current Technology of Radial-Inflow Turbines for Compressible Fluids , J. of Eng. For Power. Trans. Am. Soc. Mech. Engrs., 85 (1963)... 

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