Voltammetric determination of homovanillic acid and vanillylmandelic acid on a disposable electrochemical measuring cell system with integrated carbon composite film electrodes

Abstract

An array of carbon composite electrodes embedded in a 96-well microtitration plate was applied to differential pulse voltammetry determination of standards of tumor biomarkers 2-(4-hydroxy-3-methoxy-phenyl) acetic acid (homovanillic acid, HVA) and (RS)-hydroxy(4-hydroxy-3-methoxy-phenyl) acetic acid (vanillylmandelic acid, VMA). For the preparation of composite electrodes, graphitic conductive microparticles and nonconductive polystyrene binder were used. For the measurement, a buffer of pH 2 was selected as the optimum medium for both analytes. In this medium, concentration dependences of stand-alone standards were measured; calculated quantification limits were 0.3 µmol dm−3 for HVA and 0.8 µmol dm−3 for VMA. Sorption of analytes on employed working electrode was examined in order to verify, whether the current is influenced by the time period between cell filling and measurement. The sorption was not observed and the current was stable even after 10 min. Developed method was verified by the determination of a mixture of standards of both analytes. Mixtures of analytes of various proportions were measured and the obtained calibration curves showed good agreement with standard values. Furthermore, the results showed that the behavior of the mixture of analytes is not different from the behavior of the actual standards, so that it is possible to calculate the concentration of both analytes side by side.