Retention Characteristics of Co⁺³, Fe⁺³, and Cu⁺² 4-(2-Pyridylazo)Resorcinol (PAR) Complexes on C-18 and Amino Silica Packings

Abstract

Chloroform extraction of Co-PAR, Fe-PAR, and Cu-PAR complexes in a pH 6.5 phosphate buffer implied the first two species were primarily monoanions, but the latter was a dianion. Examination of the literature and retention data of these complexes on C-18 and amino columns confirmed the more anionic nature of Cu-PAR. The Co⁺³ and Cu⁺² complexes were slightly resolved from each other, but the Fe⁺³ complex was retained longer on the C-18 silica. In contrast, the Co⁺³ and Fe⁺³ complexes were not resolved, but the Cu⁺² complex was well-retained on the weak anion exchange amino silica column. Use of short amino and C-18 columns in series provided a good separation of all three complexes. Detection of the metal complexes at 546 nm instead of 254 nm avoided interference by PAR and good detection limits were still maintained.