MICROTUBE FLOWING COULOMETRY

An aqueous solution containing supporting electrolyte and a small conc entration of an electroactive analyte is allowed to flow, under a grav itational head, through a polarized platinum tube. The tube is narrow enough that, during their few seconds of residence time within the tub e, 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 ele ctric current, the latter being background-corrected by subtracting th e current under no-flow conditions. Though the detailed theory is comp licated, the principles of the method and its experimental realization are straightforward.