A Pencil Graphite Electrode In Situ Modified by Monovalent Copper: a Promising Tool for the Determination of Methylxanthines

A pencil graphite electrode (PeGE) exhibits a promising tool for the electrochemical analysis of xanthine (Xan) and its N-methyl derivatives (1-, 3-, 7- and 9-mXan). The changes in their level in blood, serum, urine, as products of purine catabolism, can indicate the development of some diseases. Sensitivity-enhanced voltammetric detection of mXans was achieved by forming of complex with Cu(I) and application of elimination procedure. The Cu(I)-mXan complex was identified by means of titration of electrochemically produced cuprous ions by mXan. Our approach enables separation of overlapped mXan oxidation signals. Based on the obtained results, we found that the effect of methyl group position on the xanthine skeleton was significant and it was also discussed.