Pulsed and square wave voltammetry Inventor Sir Geoffrey

Pulsed and square wave voltammetry Inventor: Sir Geoffrey Barker, Harwell, UK 1950 -60 s Modern versions. Janet and Robert Osteryoung, Univ. Colorado/SUNY Buffalo

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 -60 s by Sir Geoffrey Barker in UK, and later 1970 -80 s 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 E 60 ms time measurement Faradaic I Charging (decays faster)

Normal Pulsed Voltammetry (simplest) DL about 10 -fold lower than cyclic voltammetry (CV) Input waveform output I = IL/(1+θ) θ = {nf/RT)(E-Eo’)} IL=n. FCo*AD 1/2/(πt)1/2

Input waveforms output Normal pulse voltammetry Differential Pulse voltammetry Ep n. M detection limits

Square Wave Voltammetry – complex waveform, derivative output most sensitive instrumental electrochemical method Input waveform Ip= f(Co*, ΔE) Ep= E 1/2 – ΔE/2 output Ep n. M detection limits; Slightly better than Differential pulse

SWV outputs Net or difference current Forward Current Reverse current

NPV SWV difference current I x 1000 O 1 + e == R 2 Better resolution, Best sensitivity

SWV Output Net or difference current forward reverse

SWV parameters - increasing frequency (effect of DE is similar)

Approx DL NPV 10 -6 M/n DPV 2 x 10 -9 M/n SCV or LSV (CV) SWV 5 x 10 -5 M/n 10 -9 M/n