This work describes a unique combination of μPADs, continuous gravity-driven flow, and amperometry. We and others have demonstrated simple μPADs and electrochemical sensing using amperometry, chronoamperometry, cyclic voltammetry, and anodic stripping.5,11,12 For example, ampero- metric detection on paper has been reported after a separation with paper chromatography, using a gold electrochemical cell on polyester.13 In such demonstrations, the working electrode is generally close to the counter electrode. As a consequence, this configuration of electrodes makes the calculation of concentrations in reversible oxidation/reduction reactions complicated or ambiguous [because the ions to be analyzed, such as Fe(II)/Fe(III), can shuttle between electrodes at rates that are a priori unknown]. Analyses in which electrodes are positioned in sequence in a flowing stream of buffer are easier to interpret, as the products of the electrochemical reaction at one electrode are transported irreversibly to a second electrode or to a sink.