In
this optimization step, a small amount of the sample is dissolved in test tubes
containing various ratios of the biphasic solvent system and then partitioned
between the two phases in a test tube. Both upper and lower phases are then
examined by tlc etc. The partitioning results when examined and visualized by
TLC to give a good indication of potentially successful CCC solvents. Since
we chose the organic phase as the stationary phase ( reverse phase operation
of the CCC ) the amount of methanol in the aqueous phase is varied, in order
to pull the compounds from the organic phase into the mobile aqueous phase as
the amount of methanol increases.
Note : Whilst this technique of
tlc/test tube partitioning screening often proves to be accurate in predicting
suitable CCC solvents, as we show for this example, it is not universally
successful. Researchers should be aware that successful test tube partitioning
/ tlc does not guarantee successful CCC, plus a lack of resolution by tlc
does not mean that this system may not be successful by CCC. Often it is best
to do a generic CCC gradient to predict which solvent will be appropriate
( Dr Les Brown, is available to Quattro users / potential purchasers to discuss
any CCC applications ).
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