Influence of ligand nature on the retention of heterocyclic azonaphthols and their chelates in thin-layer chromatography

The retention of Ni(II), Fe(III), Co(LI, III), Cu(II), and Pd(II) chelates of heterocyclic azonaphthols [1-(2-pyridylazo)-2-naphthol (PAN), 1-(2-thiaz olylazo)-2-naphthol (TAN), 1-(5-chloro-2-pyridylazo)-2-naphthol(CI-PAN), 1- (5-bromo-2-pyridylazo)-2-naphthol (Br-PAN), 1-(5-bromo-2-thiazolylazo)-2-na phthol (Br-TAN), and 1-(8-quinolylazo)-2-naphthol (QAN)] was comparatively studied by thin-layer chromatography on silica gel (Silufol plates). For th e majority of studied stationary phases and chelates, mobility increases in the order CI-PAN < TAN < PAN < QAN, which corresponds to the order of prot onation constants of the heterocycle nitrogen atom. The mobility of Br-TAN chelates is higher than that of TAN chelates. In reversed-phase high-perfor mance liquid chromatography, the retention increases in the order PAN < CI- PAN < Pr-PAN; TAN < Br-TAN, which is opposite to the order of retention in thin-layer chromatography. Evidently, it is the solubility of reagents and chelates in the mobile phase that determines their chromatographic behavior in thin-layer chromatography.