Reversed-phase thin-layer chromatography of 2-substituted benzoic acids with ammonium compounds as ion-pair reagents

Summary The retention behaviour of some substituted benzoic acids was tested on reversed-phase pre-coated plates in the presence of ammonium bromide and various tetraalkylammonium compounds with different alkyl chain lengths.It could be shown that the R_f values of the test compounds decrease in the absence and in the presence of ion-pair reagents with increasing water content of the eluent. The R_f values of the strongly acidic substituted benzoic acids decrease with both increasing concentration of the ion-pair reagent and with increasing chain length of the tetraalkylammonium compounds.Changing the inorganic counter-ions had no real influence on the separation and the size of R_f values when using tetramethylammonium compounds as ion-pair reagents.