Report

Pulsed and square wave voltammetry Digital voltammetry waveforms – staircase used to approximate a ramp for LSV; All modern potentiostats use this approach, also easy to use other input waveforms All sorts of pulsed voltammetry methods were developed in 1950-60s by Sir Geoffrey Barker in UK, and later 1970-80s modernized by Janet and Bob Osteryoung in the US Basis of all pulsed methods: Response of reversible system to a potential pulse; Measuemenst at end of pulse discriminates against charging current 60 ms E time measurement Faradaic I nFAD1/o 2Co* IF (t)1/ 2 (1 ) Charging (decays faster) Idl (E /Rs )exp{ t /Cd Rs} exp[nF /RT(E E o ')] Normal Pulsed Voltammetry (simplest) DL about 15-fold lower than cyclic voltammetry (CV) Input waveform output Input waveforms output Normal pulse voltammetry Differential Pulse voltammetry Ep nM detection limits Square Wave Voltammetry – complex waveform, derivative output most sensitive instrumental electrochemical method Input waveform Ep output nM detection limits; Slightly better than Differential pulse SWV outputs Net or difference current Forward Current Reverse current NPV SWV difference current I x 1000 O1 + e == R1 R1 + e == R2 Better resolution, Best sensitivity SWV Output Net or difference current forward reverse SWV parameters - increasing frequency (effect of E is similar) Approx DL NPV 10-6 M/n DPV 2x10-9 M/n SCV or LSV (CV) SWV 5x10-5 M/n 10-9 M/n