The behaviour of an electrochemical detector used in liquid chromatography and continuous flow voltammetry: Part 1. Mass transport-limited current

Abstract

A simple expression relating the current at a rectangular channel-type flow-through electrode to the volume flow rate of solution, cell dimensions and physical constants is derived. The expression for steady-state current is valid for laminar flow with neglect of longitudinal depolarizer diffusion. The equation is derived to extract information on the analytical utility of these cells, i.e. signal-to-noise ratio (SNR). For standard amperometric detection the optimum cell design is one in which the width of the cell is equal to the width of the electrode and the length and thickness of the cell are as small as possible, the limit of these dimensions either being physical or dictated by amplifier noise in the output. There is no optimum shape for an electrode of a given size. For standard amperometric detection with a constant cell volume, V, the optimum dimensions are given by b = ( VD 0.42 U) 1 2 , ( b = thickness, D = diffusion coefficient, - U= average volume flow rate). For flow rate-modulated operation, the optimum thickness is vanishingly small, and the electrode area (shape not critical) is given by A = 0.52 Ub D -1.