SEPARATION AND DETERMINATION OF METAL-IONS WITH 2-NITROSO-1-NAPHTHOL-4-SULFONIC ACID BY HIGH-PERFORMANCE CAPILLARY ELECTROPHORESIS

Capillary electrophoresis study was carried out by using 2-nitroso-1-naphthol-4-sulfonic acid (nitroso-NW acid) as a chelating and chromogenic agent. Nitroso-NW acid (H2R) reacts with Co2+ to form the chelate anion, CoR3(3-), and also reacts with Fe2+, Ni2+, Cu2+ and Pd2+. However, except for Ni2+ and Cu2+, sharp peaks could not be obtained with a conventional carrier containing HR- and buffer components. This is probably because the metal chelates were highly charged: the chelates of Ni2+, Cu2+, Fe2+, Co2+ and Pd2+ are expected to be CuR2(2-), Fe(II)R3(4-), Co(III)R3(3-), NiR3(4-) and Pd(OH)2(2)R-, from their electrophoretic mobilities. The peaks of Fe2+, Co2+ and Pd2+ were sharpend by adding a quaternary ammonium ion to the carrier. The quaternary ammonium ion in,the carrier acts as a pairing cation of metal chelate anions. Of these, tetrabutylammonium ion(TBA+) was the best pairing ion for the metal chelates. By using a carrier containing HR-, TBA+ . Br- and buffer components (pH 7) good separation and highly sensitive detection of the five metal ions (Fe2+, Co2+, Ni2+, Cu2+ and Pd2+) could be achieved within 7 min. The proposed method was applied to the determination of cobalt in nickel salts.