Microtube flowing coulometry

An aqueous solution containing supporting electrolyte and a small concentration of an electroactive analyte is allowed to flow, under a gravitational head, through a polarized platinum tube. The tube is narrow enough that, during their few seconds of residence time within the tube, virtually all the analyte molecules are able to diffuse to the tube wall and be electrolytically destroyed. The analyte concentration is accurately calculable, when the applied voltage and head are optimized, from the measured flow rate of the solution and the steady-state electric current, the latter being background-corrected by subtracting the current under no-flow conditions. Though the detailed theory is complicated, the principles of the method and its experimental realization are straightforward.