Pulsed and square wave voltammetry. Digital voltammetry waveforms – staircase used to approximate...

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 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

Idl (E /Rs)exp{ t /CdRs}

IF nFAD o

1/ 2Co*

(t)1/ 2(1 )

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

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

outputnM detection limits;Slightly better thanDifferential pulse

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