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The Initial Stage of the Development of Planar Chromatograms

The aim of the work discussed in this paper was to re-investigate the initial stage of the retention process in TLC, namely the moment of first contact between the analyte deposited at the origin and the mobile phase employed. It was our intention to assess the impact of dissolution of the analyte by the mobile phase on the overall mobility of the analyte in the chromatographic system. To accomplish this goal parallel experiments were performed with analyte samples applied to the stationary phase and chromatographed with and without drying (i.e. with and without evaporation of the solvent used to dissolve the analyte). As test analytes we selected two compounds (5-phenylpentanol and 2-phenylbutyric acid) able to participate in lateral interactions by hydrogen bonding and another four compounds (anthracene, phenanthrene, perylene, and tetralin) totally unable to self-associate. The results obtained are presented in two different ways, i.e. as the dependence of densitometrically measured concentration profiles and of retardation factors (RF) on the amount of analyte and on the mode of application (dry or wet) to the stationary phase layer. It was discovered that for both types of analyte (i.e. participating and not participating in lateral interactions) the process of dissolution at the origin is time-consuming and thus contributes to the overall retardation of migration of the analytes.