Chemometric characterization of the RF values of pesticides in thin-layer chromatography on silica with mobile phases comprising a weakly polar diluent and a polar modifier. Part V

摘要

Relationships between RF values and mobile phase composition have been determined for the last twenty of almost one hundred pesticides studied in this work. Chromatography was performed on silica gel (and other adsorbents) with mobile phases comprising a weakly polar diluent (heptane) and a polar modifler (ethyl acetate, tetrahydrofuran, or dioxane). The relationships obtained constitute a retention database. Group selectivity was compared by use of correlation between RF coefficients, by analogy with two-dimensional TLC. The greatest spread of points, indicative of the highest selectivity, was obtained by use of non-aqueous mobile phases on silica and by use of the aqueous mobile phase methanol-water, 60 + 40 (v/v) on water wettable octadecyl silica (RP-18W). The most selective systems (normal- and reversed-phase) were chosen for separation of a mixture of nine pesticides; these were fully separated by two-dimensional development (2D TLC) on a TLC plate comprising coupled layers of octadecyl silica (reversed-phase, RP) and plain silica (normal-phase, NP).