Differential pulse voltammetry
Encyclopedia
Differential Pulse Voltammetry
(AKA Differential Pulse Polarography
or DPP) is often used to make electrochemical
measurements. It can be considered as a derivative of linear sweep voltammetry
or staircase voltammetry
, with a series of regular voltage pulses superimposed on the potential linear sweep or stair steps. The current is measured immediately before each potential change, and the current difference is plotted as a function of potential. By sampling the current just before the potential is changed, the effect of the charging current can be decreased.
By contrast, in normal pulse voltammetry the current resulting from a series of ever larger potential pulses is compared with the current at a constant 'baseline' voltage. Another type of pulse voltammetry is squarewave voltammetry
, which can be considered a special type of differential pulse voltammetry in which equal time is spent at the potential of the ramped baseline and potential of the superimposed pulse.
. The potential
between the working electrode
and the reference electrode
is changed as a pulse
from an initial potential to an interlevel potential and remains at the interlevel potential for about 5 to 100 milliseconds; then it changes to the final potential, which is different from the initial potential. The pulse is repeated, changing the final potential, and a constant difference is kept between the initial and the interlevel potential. The value of the current between the working electrode and auxiliary electrode
before and after the pulse are sampled and their differences are plotted versus potential
properties of extremely small amounts of chemicals because of the following two features:
(1) In these measurements, the effect of the charging current can be minimized, so high sensitivity
is achieved.
(2) Faradaic current
is extracted, so electrode reactions can be analyzed more precisely.
(1) Reversible reactions show symmetrical
peaks, and irreversible reactions show asymmetrical peaks.
(2) The peak potential is equal to E1/2r-ΔE in reversible reactions, and the peak current is proportional to the concentration.
(3) The detection limit is about 10-8 M.
Voltammetry
Voltammetry is a category of electroanalytical methods used in analytical chemistry and various industrial processes. In voltammetry, information about an analyte is obtained by measuring the current as the potential is varied.- Three electrode system :...
(AKA Differential Pulse Polarography
Polarography
Polarography is a subclass of voltammetry where the working electrode is a dropping mercury electrode or a static mercury drop electrode ., useful for its wide cathodic range and renewable surface...
or DPP) is often used to make electrochemical
Electrochemistry
Electrochemistry is a branch of chemistry that studies chemical reactions which take place in a solution at the interface of an electron conductor and an ionic conductor , and which involve electron transfer between the electrode and the electrolyte or species in solution.If a chemical reaction is...
measurements. It can be considered as a derivative of linear sweep voltammetry
Linear sweep voltammetry
Linear sweep voltammetry is a voltammetric method where the current at a working electrode is measured while the potential between the working electrode and a reference electrode is swept linearly in time...
or staircase voltammetry
Staircase voltammetry
Staircase voltammetry is a derivative of linear sweep voltammetry. In linear sweep voltammetry the current at a working electrode is measured while the potential between the working electrode and a reference electrode is swept linearly in time...
, with a series of regular voltage pulses superimposed on the potential linear sweep or stair steps. The current is measured immediately before each potential change, and the current difference is plotted as a function of potential. By sampling the current just before the potential is changed, the effect of the charging current can be decreased.
By contrast, in normal pulse voltammetry the current resulting from a series of ever larger potential pulses is compared with the current at a constant 'baseline' voltage. Another type of pulse voltammetry is squarewave voltammetry
Squarewave voltammetry
Squarewave voltammetry is a further improvement of staircase voltammetry which is itself a derivative of linear sweep voltammetry. In linear sweep voltammetry the current at a working electrode is measured while the potential between the working electrode and a reference electrode is swept...
, which can be considered a special type of differential pulse voltammetry in which equal time is spent at the potential of the ramped baseline and potential of the superimposed pulse.
Electrochemical Cell Set-Up
The system of this measurement is usually the same as that of standard voltammetryVoltammetry
Voltammetry is a category of electroanalytical methods used in analytical chemistry and various industrial processes. In voltammetry, information about an analyte is obtained by measuring the current as the potential is varied.- Three electrode system :...
. The potential
Potential
*In linguistics, the potential mood*The mathematical study of potentials is known as potential theory; it is the study of harmonic functions on manifolds...
between the working electrode
Working electrode
The working electrode is the electrode in an electrochemical system on which the reaction of interest is occurring. The working electrode is often used in conjunction with an auxiliary electrode, and a reference electrode in a three electrode system...
and the reference electrode
Reference electrode
A reference electrode is an electrode which has a stable and well-known electrode potential. The high stability of the electrode potential is usually reached by employing a redox system with constant concentrations of each participants of the redox reaction.There are many ways reference...
is changed as a pulse
Pulse
In medicine, one's pulse represents the tactile arterial palpation of the heartbeat by trained fingertips. The pulse may be palpated in any place that allows an artery to be compressed against a bone, such as at the neck , at the wrist , behind the knee , on the inside of the elbow , and near the...
from an initial potential to an interlevel potential and remains at the interlevel potential for about 5 to 100 milliseconds; then it changes to the final potential, which is different from the initial potential. The pulse is repeated, changing the final potential, and a constant difference is kept between the initial and the interlevel potential. The value of the current between the working electrode and auxiliary electrode
Auxiliary electrode
The Auxiliary electrode, often also called the counter electrode, is an electrode used in a three electrode electrochemical cell for voltammetric analysis or other reactions in which an electrical current is expected to flow...
before and after the pulse are sampled and their differences are plotted versus potential
Uses
These measurements can be used to study the redoxRedox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
properties of extremely small amounts of chemicals because of the following two features:
(1) In these measurements, the effect of the charging current can be minimized, so high sensitivity
Sensitivity (electronics)
The sensitivity of an electronic device, such as a communications system receiver, or detection device, such as a PIN diode, is the minimum magnitude of input signal required to produce a specified output signal having a specified signal-to-noise ratio, or other specified criteria.Sensitivity is...
is achieved.
(2) Faradaic current
Faradaic current
The faradaic current is the current generated by the reduction or oxidation of some chemical substance at an electrode. The net faradaic current is the algebraic sum of all the faradaic currents flowing through an indicator electrode or working electrode....
is extracted, so electrode reactions can be analyzed more precisely.
Characteristics
Differential pulse voltammetry has these characteristics:(1) Reversible reactions show symmetrical
Symmetry
Symmetry generally conveys two primary meanings. The first is an imprecise sense of harmonious or aesthetically pleasing proportionality and balance; such that it reflects beauty or perfection...
peaks, and irreversible reactions show asymmetrical peaks.
(2) The peak potential is equal to E1/2r-ΔE in reversible reactions, and the peak current is proportional to the concentration.
(3) The detection limit is about 10-8 M.
External links
- http://www.drhuang.com/science/chemistry/electrochemistry/polar.doc.htm
- http://pubs.acs.org/doi/pdf/10.1021/ed073p544?cookieSet=1