SOLVENT DEMIXING EFFECTS IN CONTINUOUS THIN-LAYER CHROMATOGRAPHY AND THEIR ELIMINATION

Demixing effects in thin-layer chromatography have been investigated for frequently used binary solvents of various compositions, and methods of eliminating such effects are described. The simplest way of eliminating solvent demixing consists in presaturation of the plate in the vapours of the polar solvent component or pre-development with its more concentrated solution. The sample should be spotted some distance behind the front of the developing solvent to secure steady-state conditions analogous to column development with an equilibrated mobile phase. For more concentrated polar solvents (e.g., ≫ 20%) it is sufficient to spot the sample several centimetres behind the solvent front; the RF values of solvent demixing are then high so that the presaturation or predevelopment step can be omitted. Procedures for the elimination of solvent demixing for typical solvent mixtures in the minimum time are given in terms of the distance of predevelopment. © 1979.