Photometric determination of aqueous cobalt (II), nickel (II), copper (II) and iron (III) with 1-nitroso-2-naphthol-3,6-disulfonic acid disodium salt in gelatin films

Abstract

Photometric determination of aqueous Co(II), Cu(II), Ni(II) and Fe(III) was performed using indicator films prepared by immobilization of 1-nitroso-2-naphthol-3,6-disulfonic acid disodium salt (NRS) into hardened photographic film. Immobilization was based on electrostatic interaction of reagent and metal complexes with the gelatin. The isoelectric point pH of hardened gelatin (4.46±0.04) was evaluated by viscometry. Co(II), Fe(III), Ni(II) form 1:3 complexes with NRS in gelatin at pH 2 and Cu(II) forms 1:2 complexes. Their log β' values were: Co-6.7, Fe-8.6, Cu-8.0, and Ni-6.4. The absorption maxima were: 370 nm for NRS, and 430 nm, 470 nm, 495 nm and 720 nm for complexes of Co(II), Ni(II), Cu(II) and Fe(III). An algorithm for their simultaneous determination using the indicator films was developed. The detection limits were: C lim(Co 2+) = 0.45×10-5 M, C lim(Fe 3+) = 0.50×10 -5 M, C lim(Cu 2+) = 0.67×10 -5 M, C lim(Ni 2+) = 0.75×10 -5 M,; and their sum C lim(∑M n+) = 0.82×10 -5 M. © Versita Sp. z o.o.