A protocol controlling the analytical cycles of the proposed SIA procedure was programmed. Following this protocol, a sample solution (600 μL) was aspirated into the HC using the SP. After flow reversal, the sample zone was transported to the electrochemical FC at the required flow rate (2–20 μL/s). During the contact time between the sample and the working electrode, the analyte accumulated onto the electrode surface at an open circuit. After accumulation step, 0.1 M PBS was propelled through the FC. A stripping voltammogram was recorded under the stopped-flow conditions in the anodic potential range from 0.2 V to 1.4 V. The resulting stripping peak current of purine nucleobases was measured. Before the beginning of a new sample pre-treatment step, for removing adsorbed compounds, the electrode surface was regenerated by scanning potential (number of scans = 5) in the blank PBS for about 7 cycles. HClO4 was used to on-line activate the electrode surface, when necessary.