Pulsed and square wave voltammetry
description
Transcript of Pulsed and square wave voltammetry
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