Determination of L-DOPA at an optimized poly(caffeic acid) modified glassy carbon electrode
A thin layer of poly(caffeic acid) was electrodeposited onto the surface of a glassy carbon (GC) electrode under potentiostatic conditions in aqueous solution. This system was utilized for the detection of 3,4-dihydroxy-L-phenylalanine (L-DOPA) by square wave voltammetry (SWV) after the experimental parameters of pH, step, amplitude, and frequency were studied by a full factorial design (FFD) to identify the significant parameters and their interactions. The results showed that pH, step, and amplitude were significant, whereas frequency did not significantly impact response. Subsequently, a central composite design (CCD) was performed for the three significant factors in order to further optimize the method. The optimum conditions were pH: 4.8; step potential: 5 mV; amplitude: 88 mV. Under these optimized conditions, the modified electrode demonstrated high selectivity for L-DOPA in the presence of common biological interferences such as ascorbic acid and uric acid by the observation of three distinctive and well resolved oxidation peaks. The sensor was simple to prepare, provided short analysis times, and exhibited a linear range from 1.0–50.0 μM with a detection limit of 0.14 μM for analysis of L-DOPA.