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VOLTAMMETRY

By

Kristeen Garcia

Racia Carlane Fabregas

Kriszel Cafirma

Anne Rejane Drueco

Fatima Johara Lakkian

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VOLTAMMETRY

Voltammetry is the name of a group of electrochemical techniques where current

is studied as a response to potential. Voltammetry provides information about thethermodynamics and kinetics of chemical reactions and identifies different

species in solution.

How it works

The electrochemical cell, where the voltammetric experiment is carried out,

consists of a working electrode, a reference electrode, and usually an auxiliary

electrode. The working electrode, which makes contact with the analyte, must

apply the desired potential in a controlled way and facilitate the transfer of chargeto and from the analyte.The reference electrode is a half cell with a known

reduction potential. Its only role is to act as reference in measuring and

controlling the working electrodes potential and at no point does it pass any

current. The auxiliary electrode passes all the current needed to balance the

current observed at the working electrode. To achieve this current, the auxiliary

will often swing to extreme potentials at the edges of the solvent window, where it

oxidizes or reduces the solvent or supporting electrolyte.

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General Theory

In voltammetry, the effects of the applied potential and the behavior of the redox

current are described by several well-known laws. The applied potential controls

the concentrations of the redox species at the electrode surface and the rate of

the reaction, as described by the Nernst or ButlerVolmer equations.

Nernst Equation - deals with cell potential as well as energy of chemical

reactions where the energy created gives rise to the cell potential of a

system called galvanic cell.

The general Nernst equation correlates the Gibb's FreeEnergyG and the EMF of a chemical system known as the galvaniccell. For the reaction:

a A + b B = c C + d Dand

[C]c [D]d

Q= ---------[A]a [B]b

It has been shown thatG =G + R Tln QandG = - n FE.

Therefore

- n F

E= - n F

E + R Tln Q where R, T, Q and Fare the gasconstant (8.314 J mol-1 K-1), temperature (in K), reaction quotient,and Faraday constant (96485 C) respectively. Thus, we have

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Square Wave Voltammetry

Cyclic Voltammetry

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Chronoamperometry

Anodic Stripping Voltammetry

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Differential Pulse Voltammetry

Polarography

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Heyrovskho Polarograph

Applications

o Quantitative determination of pharmaceutical compounds

o Determination of metal ion concentrations in water to subparts-per-billion

levels

o Determination of redox potentials

o Detection of eluted analytes in high-performance liquid chromatography

(HPLC) and flow injection

o Analysis

o Voltammetric sensors

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o Oxygen electrode