Other Chromatographic Approaches

Substances with high K values that are not eluted, will be to some extent separated along the column and can be recovered by stopping the apparatus and pumping out the column contents. An alternative approach is to switch phases without stopping the chromatogra-phy. In the MLCPC, the appropriate directions for pumping the phases is head to tail for the heavy phase and tail to head for the lighter phase, so this approach involves switching the column inlet as well. For the CDCCC, the corresponding directions are downward for heavy phase and upward for lighter phase.

Yet another approach to manipulating CCC is to fill the column initially with a non-equilibrium ratio of phase volumes by simultaneously filling both phases at once. Retention of particular K values can be enhanced or diminished by choosing the appropriate phase-volume ratio. Gradients can also be used for a number of systems, particularly where the composition of the stationary phase changes very little as the polarity of the mobile phase is changed.

For acidic and basic substances, adjustment of pH or use of a pH gradient can be useful. The range of pH is not a limitation as far as the apparatus is concerned. Ion-pair formation and use of liquid-ion exchangers can also be exploited, and various chelat-ing agents have been used for the separation of metals, particularly rare earths. Optical resolutions have been achieved by addition of chiral selectors predominantly soluble in one of the phases to the solvent system.

The above examples indicate a few of the many ways in which CCC apparatus can be manipulated to achieve separations by means other than straightforward chromatography.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

Get My Free Ebook

Post a comment