Voltammetry and Polarography

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Voltammetry and Polarography

• Chapter 9

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• 9A Polarography
• 9B Linear-Sweep Voltammetry and Cyclic
  Voltammetry
• 9C Pulse Polarographic and Voltammetric Methods
• 9D Polarography Catalytical Waves
• 9E Stripping Voltammetriy

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Intruduction
Voltammetry and Polarography
i-E curves
Differences
Polarograph dropping mercury electrode (DME)
Voltammetric Methods GCE metal electrodes
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9A Polarograpy
9A-1 Instrumentation
(b)
(a)
(a)
Figure 9A-1 (a) Jaroslav Heyrovsky (1890-1967)
was awarded the 1959 Nobel Prize in chemistry for
his discovery and development of polarography.(b)
The first Polarography .
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9A-2 Polarogram
DME cathodic
Calomel anode
Figure 9A-2 The polarogram of Pb2
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Working electrode(indicated electrode)DME Referen
ce electrode Supporting electrolyte Remove
oxygen Stationary solution
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i K(Pb2-Pb20)
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Quantitative analysis
Qualitative analysis
Half-potential (E1/2)
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Conttroll Equation
Ilkovic Equation
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Interfering current Remove Residual
current Migration current
KCl, NH4Cl, KNO3 Maximum current
surfactant Oxygen waves
N2
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9A-3 Polarography Equation
Simple metal ions Reversible process
Reduction reaction
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Metal complex reversible process Reduction
reaction
Application ???????????
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Disadvantage Need more mercury and time Low
resolution Low sensitivity iR drop
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9 B Linear-Sweep Voltammetry and Cyclic
Voltammetry
9B-1 Linear-Sweep Voltammetry
scan one time in a drop of mercury
Polarography
Linear scan
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Quantitative Analysis (1)Randles-Sevcik?? Reversi
ble reaction ip Kn3/2Do1/2m2/3tp2/3v1/2C Rand
les K 2344, Sevcik K 1852 ip (mA)
Do(cm2/s) m(mg/s)tp(s)v(V/s)C(mM)  i n3/2
F3/2/R1/2T1/2 A Do1/2v1/2CP (nFvt/2RT) P(nFvt/2R
T) 0.447, 0.452,0.4463
(2)Plane electrode Diffusion current equation ip
2.69 x105n3/2Do1/2Av1/2C ip(A)
Do(cm2/s)A(cm2)v(V/s) C (mol/cm3) ip(A)
C(mol/L) , K269 1mol/cm3 10 3 mol/L
Ip(mA) C (mol/L) , K2.69 x105
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Quantitative Analysis
Reductive wave
Oxidative wave
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Characters

• One drop of mercury
• Simple and fast process
• High sensitivity partly remove ic
• Strong resolution

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9B-2 Cyclic Voltammetry
Basic principles
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Voltammetric Electrodes take a variety of shapes
and forms, which include small flat disks of a
conductor .The conductor may be inert metal .
such as platinum or gold pyrolytic graphite or
glassy carbon or a metal coated with a film
mercury.
Figure 9B-2 Accessible potential window of
platinum, mercury, and carbon electrodes in
supporting electrolytes.
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Application 1. To determine the reversibility of
electrode process (1)Reversible electrode
process
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(2) Irreversible electrode process
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Potassium ferricyanide voltammogram
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2. Mechanism of electrode reaction Ru(NH3)5Cl2
Fast scan rate Ru(NH3)5Cl2 e- Ru(NH3)5Cl
Slow scan rate, the emergence of a new redox
peaks Ru(NH3)5Cl2 H2O Ru(NH3)5H2O 2 Cl-
Ru(NH3)5H2O 3 e- Ru(NH3)5H2O 2
Voltammogram of Ru(NH3)5Cl2
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• Application
• (1) Oxidation and reduction processes in various
  media
• (2) Adsoption processes on surfaces
• (3) Electron transfer mechanisms at chemically
  modified electrode surfaces.

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9C Pulse Polarographic and Voltammetric Methods
Basic Principles Normal Pulse Polarography
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Differtail Pulse Polarography
remove ic and ib
Adervantage
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9D Polarographic Catalytic Wave
9D-1 Theory of Polarographic Catalytic Wave
Chemical reaction parallel to electrode reaction
Dynamical wave
Improve the signal to noise ratio Signal
/Noise
(electrode reaction)
(chemical reaction)
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Categories
Parallel polarographic catalytic wave Hydrogen
catalytic wave Adsorptive complex wave
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9D-2 Parallel Polarographic Catalytic Wave
O ne
R
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Parallel catalytic wave equation for the
catalytic current ic
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9D-3 Hydrogen Catalytic Wave
at DME Some nitrogen-containing,
sulfur-containing organic compounds or their
metal complexes
Determine amino acids, proteins.
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9D-4 Adsorptive Complex Wave
High sensitivity
10-710-9 mol L-1
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9E Stripping Voltammetry
Combination of Electrolytic enrichment and
stripping analysis
Categories
stripping
Anodic stripping voltammetry oxidation
reaction
Cathodic stripping voltammetry reduction
reaction
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Stripping Analysis Concentration step
electrolysis,
adsorption Stripping step Potential, Current,
Chemical
reaction Recording permanents
I-E, E-t, Q-t, Q-E Detection limit
10-12 M
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9E-1 Anodic stripping voltammetry
Deposition
Stripping
Curve of Anodic stripping voltammetry
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9E-2 Cathodic stripping voltammetry
Determine Cl-,Br-,I-,S2-,C2O42-
Sulfide stripping voltammetry curves
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9E-3 Working Electrodes in Stripping Voltammetry

Mechanical compression-type rotary mercury
electrode
Silver-based mercury film electrode
HMDE
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Rotating Ring-Disk Electrode
Disk electrode
Ring electrode
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Chemical modified electrode
Example
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specific analyte or group of analytes. While the
signal may in principle be continuous, devices
can be configured to yield single measurements to
meet specific market requirements. Applications
in medicine, drug discovery, the environment,
food, process industries, security and defence.
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