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

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.