Study of the Performances of Thin Layer Chromatography. V. Flow Rate in Reversed Phase Plates

Abstract

The conventional equation for the development of TLC plates predicts a velocity constant proportional to the cosine of the wetting angle of the surface by the mobile phase. Because silica is wet by all organic solvents used in normal TLC, this dependence was never checked. The development of reversed-phase TLC plates using chemically bonded n-alkyl silica offers a new situation as water-rich solvent mixtures do not wet these surfaces completely. Comparison of velocity constants measured in TLC using plates made with various adsorbents and contact angles measured directly shows the validity of the conventional equation and the cos θdependence. As a consequence, it takes an impractically long time to develop TLC plates using water/alcohol mixtures containing more than ca. 25–40% water (v/v) depending on the adsorbent, which limits the applicability of reversed-phase TLC in practical analysis.