Two-stage fractionation of a mixture of pesticides by micropreparative TLC and HPLC

Abstract

A ten-component mixture of pesticides was applied to the edge of the layer in 'frontal + elution' mode for preliminary fractionation by zonal micropreparative TLC. The separated, simpler, fractions were applied to an octadecyl silica layer wettable with water (TLC, RP-18W) and re-chromatographed. The plate was scanned and videoscanned, furnishing a real picture of the plate and showing complete separation of the fractions. The simpler fractions were also analyzed by HPLC on an octadecyl silica (LC-18) column. Preparative separation of the complex mixtures by TLC on silica (non-aqueous mobile phase, normal-phase (NP) chromatography) combined with TLC or HPLC (aqueous mobile phase, reversed-phase (RP) chromatography) results in the strong possibility of full separation of the simpler fractions in the second stage by use of the two independent methods, owing to the different selectivity of NP and RP systems (TLC and HPLC).