Pulsed and square wave voltammetry

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

2. 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

3. 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)

4. 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=nFCo*AD1/2/(πt)1/2

5. Input waveforms output Normal pulse voltammetry Differential Pulse voltammetry Ep nM detection limits

6. Square Wave Voltammetry – complex waveform, derivative output most sensitive instrumental electrochemical method Input waveform Ip= f(Co*, ΔE) Ep= E1/2 – ΔE/2 output Ep nM detection limits; Slightly better than Differential pulse

7. SWV outputs Net or difference current Forward Current Reverse current

8. NPV SWV difference current I x 1000 O1 + e == R1 R1 + e == R2 Better resolution, Best sensitivity

9. SWV Output Net or difference current forward reverse

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

11. Approx DL NPV 10-6 M/n DPV 2x10-9 M/n SCV or LSV (CV) 5x10-5 M/n SWV 10-9 M/n