Trace assay of insulin in a pharmacy drug with a paste electrode

This paper describes the development of a voltammetric assay of insulin using a DNA immobilized onto a carbon nanotube paste electrode (CNPE), the peak potential of which was 0.2 V, vs. Ag/AgCl on the CNPE. The cyclic voltammetry (CV) and square-wave (SW) stripping voltammetry parameters of the optimized conditions were determined. Low analytical working ranges of 10-80 ugL^-1 CV and 0.01-0.1 ngL^-1 SW were attained. The precision of the insulin concentration of 0.01 ugL^-1 was 0.14 (n = 15) RSD using the optimum conditions, in which the detection limit was 0.004 ngL^-1 (6.9 × 10^-12 M) (S/N = 3) using only an accumulation time of 400 s. The developed method was applied to determine insulin in a pharmacy drug from analytical-grade chemicals (from Aldrich).