TRACE MEASUREMENTS OF INSULIN BY POTENTIOMETRIC STRIPPING ANALYSIS ATCARBON-PASTE ELECTRODES

A potentiometric stripping method for trace measurements of insulin at carbon paste electrodes is described. The method is based on the cont rolled adsorptive accumulation of this polypeptide hormone at the anod ically pretreated carbon surface followed by constant-current chronopo tentiometric measurements of the surface species. A well-defined peak. associated with the oxidation of the tyrosine residues, is observed o ver the flat baseline of tile potentiometric stripping operation. Vari ables of the pretreatment and measurement steps are optimized to offer a detection limit of 2 x 10(-9) hi after 5 min preconcentration. Exce ss of numerous potential interferences does not influence the response observed after transferring the electrode (with the accumulated insul in) to a blank electrolyte solution. A similar protocol is described f or trace measurements of the protein myoglobin.