Iridium-Based Electrocatalytic Systems for the Determination of Insulin

摘要

Two electrochemical catalytic systems for the determina-tion of insulin were developed. The homogeneous sy~n was based on the oxidation of insulin by chioro complexes of iridium(lV). Kinetic studies revealed that the aqui~m of iridium complexes activated them toward the ox~im of insulin in acidic solutions; e.g., the rate constant was equal to 25,900, and 8400 Lmot1 s1 Au the .i~ of insulin by the IrClS~, Ir(HzO)CIs, h(HaO)aE~ complexes, respectively. line ~1mem d ~complexes argued for the 0uw-q3he~~d&e homogeneous oxndiiion readia.. ~edrqiIihgf~-ed indium complexes on the glansy cfrn electrode resulted in the formation of the iridium oxide (IrOx) surface film, which was used in the heterogeneous detec-tion system for insulin. The catalytic activity of the IrOx film toward insulin oxidation was ascribed to a combina-tion of electron-transfer mediation and oxygen transfer which was related to the add/base chemistry of the film. The IrOx film electrode was used as an amperometric detector for flow injection analysis of insulin in pH 7.40 phosphate buffer. linear least-squares calibration curves over the range 0.05—0.50 pM (five points) had slopes of 35.2 + 0.4 nApM’ and correlation coeffidents of 0.999. The detection limit for insulin was 20 nM using the criterion of a signal of 3 times the peak-to-peak noise. The advantageous properties of the detector based on the IrOx film are its inherent stability at physiological pH, high catalytic activity toward insulin oxidation, and simplicity of preparation.