ABSTRACT
The separation of multicomponent mixtures by thin-layer chromatography (TLC) or highperformance liquid chromatography (HPLC) under fixed experimental conditions is often complicated by large differences in the polarity of the various components. To deal with this problem, eluents of low strength are needed to separate the less strongly retained solutes, whereas the strongly retained components of the mixtures can be separated by eluents of high strength. This is referred to as the general elution problem (1), and in TLC it can be handled in various ways: gradient elution (stepwise or continuous), stationaryphase gradient, polyzonal TLC, or temperature programming. These various techniques are based on different band migration rates of the components of the mixture during the separation process.
