Transcript Slide 1

Pulsed Voltammetric Methods
Pulsed Voltammetric Techniques
Typical Set up for Polarography
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Pulsed Voltammetric Methods
DC Polarography with Dropping Mercury Electrode (DME)
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Pulsed Voltammetric Methods
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Sample-and-Hold or Tast (sampled-current) Voltammetry
E
DE
id (t )  708nDO1/ 2CO* m2 / 3t 1/ 6
t
t
id (t )  0.00567Ci m2 / 3 ( EPZC  E)t 1/ 3
Current is sampled late in the drop life,
so faradaic current is minimized versus near onset.
LOD ~ 10-5 M
Pulsed Voltammetric Methods
Normal Pulse (NPV or NPP) vs. Tast Voltammetry
id (t ) NPV
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nFADO1/ 2CO*
 1/ 2
 (t  t ' )1/ 2
Current sampled
and held.
If t
 t ' > 5RsCd (~0.05-15 ms), icharging is almost insignificant.
LOD ~ 10-5 -10-6M
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Pulsed Voltammetric Methods
Differential Pulse (DPV) vs. Normal Pulse Voltammetry
NPV
DPV
Small ifaradaic
when away
from E0’
Large ifaradaic
when near E0’
LOD ~ 10-6 -10-7 M
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Pulsed Voltammetric Methods
Comparison of Excitation Waveforms for Pulsed Voltammetries
NPV
DPV
Osteryoung
Square
Wave
Voltammetry
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Osteryoung Square Wave Voltammetry
LOD ~ 10-8 M
Pulsed Voltammetric Methods
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Pulsed Voltammetric Methods
Osteryoung Square Wave Voltammetry
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Pulsed Voltammetric Methods
Stripping Analysis Coupled to DPV - DPASV
ip = 0.138 Qmetal/tpulse-width
~50-nm thick Hg film on Glassy Carbon (vitreous)
electrode by electrodeposition from acidic Hg2+
Deposit M0
DPV
Limit of Detection of ~0.005 ppm
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