Screening solvent systems

To use CCC successfully it is necessary to empirically search for suitable solvent systems using non-CCC methods initially. The first goal is to find a system that provides a K of 1 to 2 and that provides good sample solubility in both phases. This latter point is important because sample capacity will be limited by the phase in which the sample is least soluble. Two approaches to screening K values will be described here briefly.

Using TLC Prepare a small amount of the proposed bi-phasic solvent system and partition some sample between about 200 |L of each phase. Spot 20 |L of each of the phases side by side on a TLC plate and develop with a suitable TLC system. Visual examination, or better, scanning with a TLC densitometer, of the separated spots for the two phases will allow a judgement to be made as to which of the components have K values in the neighbourhood of 1.

Using HPLC Dissolve a small amount of sample in about 500 | L of aqueous phase. Chromatograph 20 |L in a suitable HPLC system. Then equilibrate the aqueous solution with the same volume of non-aqueous phase, discard the non-aqueous extract and again chromatograph 20 | L of the aqueous phase. From the respective peak heights, the partition coefficients in the CCC solvent system can be calculated.

Since CCC retention depends only on K, using the equation for VR, or simply referring to Figure 3, the expected retention times of the sample components can be calculated.

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