Nickel (II) tetraaza macrocycle modified electrodes for the electrocatalytic determination of L-ascorbic acid by the flow injection method

1,5,8,12-Tetraaza-2,4,9,11-tetramethylcyclotetradecinatonickel(II) was synthesized for a new Ni(II) complex of the asymmetric tetraaza macrocycle and this complex was electropolymerized on a glassy carbon electrode in acetonitrile by cyclic voltammetric and constant potential methods. The modified electrodes were characterized by cyclic voltammetry and hydrodynamic voltammetry. They showed electrocatalytic effects on the oxidation of L-ascorbic acid and the peak potential shifted to the negative by 200 mV compared with that for the bare electrode in the cyclic voltammograms. In the flow injection analysis the oxidation potential of L-ascorbic acid at the modified dual glassy carbon electrode also shifted to a lower potential and the sensitivity was enhanced greatly. The amperometric determination of L-ascorbic acid by the flow injection method was performed at 0.5 V versus Ag \ AgCl \ NaCl(sat.) and the calibration curve was linear in the range of 5.0 x 10(-7) to 1.0 x 10(-3) M (R = 0.9989). The detection limit was 4.7 x 10(-7) M. The modified electrode was highly stable under the hydrodynamic conditions, which could be used for 45 repeated injections within a relative standard deviation of 5%. A GCE electropolymerized with the Ni(LI) complex of the tetraaza macrocycle was used for the determination of L-ascorbic acid in commercial beverage samples and the results were in good agreement with the labeled values and those obtained by the reference method. The analysis with the polymer modified electrodes was selective for L-ascorbic acid from the various additives in the real samples. (C) 1999 Elsevier Science S.A. All rights reserved.