Voltammetric determination of some opiates at modified carbon-based electrodes

Codeine (3-methylmorphine) is an analgesic and antitussive agent which belongs to the family of opiates naturally found in the poppy plant. In this study, the preparation of a carbon paste electrode modified with poly(guanine) as well as its novel application for the electrochemical oxidation and voltammetric determination of codeine are described. The sensitivity of the voltammetric measurements was significantly increased at modified electrode in comparison to the bare one. Besides, a further increase in the detecting sensitivity of codeine could be obtained in the presence of anionic surfactant (sodium dodecylsulfate, SDS). Using square-wave voltammetry, the compound yielded a well-defined voltammetric response in phosphate buffer (pH 4.0) containing 5×10-4 M SDS at +1.13 V (vs. Ag/AgCl). The process could be used to determine codeine in the concentration range from 2×10−7 to 3×10−6 M, with a detection limit of 1.3×10−8 M (0.4 ng mL-1). The suggested method was applied to pharmaceuticals.