Voltammetric Determination of Codeine on Glassy Carbon Electrode Modified with Nafion/MWCNTs

A glassy carbon electrode modified with a Nafion/MWCNTs composite is shown to enable the determination of codeine using differential pulse voltammetry in phosphate buffer of pH 3.0. At a preconcentration time of 15 s, the calibration graph is linear in the 0.5 µM (0.15 mg·L(−1)) to 15 µM (4.5 mg·L(−1)) concentration range with a correlation coefficient of 0.998. The detection limit at a preconcentration time of 120 s is as low as 4.5 μg·L(−1). The repeatability of the method at a 0.6 μg·L(−1) concentration level, expressed as the RSD, is 3.7% (for n = 5). The method was successfully applied and validated by analyzing codeine in drug, human plasma, and urine samples.