Transcript Pulsed and Square Wave Voltammetry

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 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
60 ms
E
time
measurement
Faradaic
I
nFAD1/o 2Co*
IF 
(t)1/ 2 (1  )
Charging (decays faster)

Idl  (E /Rs )exp{ t /Cd Rs}
  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
Normal pulse voltammetry
Differential Pulse voltammetry
Ep
nM detection limits
Square Wave Voltammetry – complex waveform, derivative output most sensitive
instrumental electrochemical method
Input waveform
Ep
output
nM detection limits;
Slightly better than
Differential pulse
SWV outputs
Net or difference current
Forward
Current
Reverse current
NPV
SWV
difference current
I x 1000
O1 + e == R1
R1 + e == R2
Better resolution,
Best sensitivity
SWV Output
Net or difference current
forward
reverse
SWV parameters - increasing frequency (effect of E is similar)
Approx DL
NPV
10-6 M/n
DPV
2x10-9 M/n
SCV or LSV
(CV)
SWV
5x10-5 M/n
10-9 M/n