Hydrodynamic ultramicroelectrodes: kinetic and analytical applications

This review considers the development and application of hydrodynamic ultra microelectrodes (H-UMEs). These electrochemical systems comprise an amperom etric UME, with a characteristic dimension on the micrometre or sub-microme tre scale, operated in a well-defined convective- diffusive regime. The gre atly enhanced mass-transport rates that can be attained quantitatively at H -UMEs, over a wide dynamic range, has considerable benefits in terms of mea suring fast kinetics and in analytical applications. Four types of H-UMEs a re assessed: (i) fast-flow tubular and channel microelectrodes; (ii) a drop ping mercury microelectrode; (iii) a microscopic wall-tube electrode, terme d the microjet electrode (MJE); and (iv) a radial flow micro-ring electrode (RFMRE). Hydrodynamic modulation methods are also described, that can be u sed in association with UMEs to extend amperometric detection limits. Final ly, possible future directions for H-UMEs are considered briefly, along wit h new methods for enhancing the timescale of dynamic electrochemical measur ements. (C) 2001 Elsevier Science Ltd. All rights reserved.