Pulsed and square wave voltammetry

Inventor: Sir Geoffrey Barker, Harwell, UK 1950-60s

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 1950-60s by Sir Geoffrey Barker in UK, and later 1970-80s modernized by Janet and BobOsteryoung in the US

Etime

Basis of all pulsed methods: Response of reversible system to a potential pulse;Measuemenst at end of pulse discriminates against charging current

I

Faradaic

Charging (decays faster)

60 ms

measurement

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

Input waveforms output

Ep

Differential Pulse voltammetry

Normal pulse voltammetry

nM detection limits

Ep

Square Wave Voltammetry – complex waveform, derivative output most sensitive instrumental electrochemical method

Input waveform

output

nM detection limits;Slightly better thanDifferential pulse

Ip= f(Co*, ΔE)

Ep= E1/2 – ΔE/2

SWV outputs

Net or difference current

Reverse current

Forward Current

NPV SWV

O1 + e == R1

R1 + e == R2

Better resolution, Best sensitivity

I x 1000

difference current

forward

reverse

Net or difference current

SWV Output

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

Approx DL

NPV

DPV

SCV or LSV(CV)

SWV

10-6 M/n

2x10-9 M/n

5x10-5 M/n

10-9 M/n