Separation efficiency of adsorption and partition thin-layer chromatography and reversed-phase high-performance thin-layer chromatography with chemically bonded phases for alkylphenoxyalkanoic acids

Abstract

The separation of 32 alkyl-substituted phenoxyalkanoic acids from phenoxyacetic to 3-pentadecylphenoxylauric acid was studied using adsorption chromatography, three types of partition chromatography (water, formamide or liquid paraffin as stationary phases) and reversed-phase high-performance thin-layer chromatography (RP-HPTLC) with chemically bonded phases. All these chromatographic systems were found suitable from the analytical point of view, but some differences in their suitability for the separation of lower or higher homologues or in their detection sensitivity were observed. The most efficient methods seem to be RP-HPTLC and TLC on silica gel layers impregnated with formamide or dimethylformamide, respectively, the former owing to the good separation of the highest lipophilic homologues and to the formation of discrete spots, permitting sharper analytical differentiation of acids with smaller Rf F differences in general, and the latter owing to the highest ΔR M values for the methylene groups of all the homologues in connection with high detection sensitivity. The best detection was achieved by using 2,7-dichlorofluorescein as the spray reagent followed by observation in UV light. The detection limit was 0.5-10 μg of the acids, depending on the chromatographic system used.