Abstract: 1,5,8,12-Tetraaza-2,4,9,11-tetramethylcyclotetradecinatonickel(II) was synthesized for a new Ni(II) complex of the asym. tetraaza macrocycle and this complex was electropolymd. 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 vs. 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 electropolymd. with the Ni(II) 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 anal. with the polymer modified electrodes was selective for l-ascorbic acid from the various additives in the real samples.

Abstract: Macrocyclic Ni(II) complex and hydrophilic polyurethane (PU) were used to modify activated glassy carbon (GC) electrodes for the electrocatalytic oxidation and selective detection of norepinephrine (NE). The Ni(II) complex was electropolymerized using cycling potentials, and the Ni(II) complex-modified electrode had a negatively shifted oxidation potential and increased current in phosphate buffer at pH 7.4. The linear range and detection limit were from 0.10 to 10^-M (390 nA?M-1, R=0.999) and 7.7 nM (signal-to-noise ratio, S/N=3) by amperometry with flow injection, respectively. The Ni(II) complex-modified electrodes were coated with hydrophilic PU for higher selectivity. Hydrophilic anionic PU was produced by the hydrolysis of PU containing ?-benzyl L-glutamate (PUBLG) segments. The hydrophilic PU-coated electrodes increased the selectivity for NE over ascorbic acid (AA) and uric acid (UA). Moreover, NE in a human urine sample was detected with higher sensitivity, reproducibility, and stability than by using Nafion-coated electrodes. Therefore, hydrophilic PU and Ni(II) complex can be used as new electrode materials for the electrocatalysis and selective electroanalysis of NE. In particular, hydrophilic PU can be used as an alternative anionic material to Nafion for better urine compatibility. © 2004 Elsevier Ltd. All rights reserved.