221:
there is initially a large increase in the surface area. As a consequence, the initial current is dominated by capacitive effects as charging of the rapidly increasing interface occurs. Toward the end of the drop life, there is little change in the surface area which diminishes the contribution of capacitance changes to the total current. At the same time, any redox process which occurs will result in faradaic current that decays approximately as the square root of time (due to the increasing dimensions of the Nernst diffusion layer). The exponential decay of the capacitive current is much more rapid than the decay of the faradaic current; hence, the faradaic current is proportionally larger at the end of the drop life. Unfortunately, this process is complicated by the continuously changing potential that is applied to the
204:
the current oscillations corresponding to the drops of Hg falling from the capillary. If the maximum currents of each drop were connected, a sigmoidal shape would result. The limiting current (the plateau on the sigmoid), is called the diffusion-limited current because diffusion is the principal contribution to the flux of the electroactive material at this point of the Hg drop life. More advanced varieties of polarography (see below) produce peaks (which allow for a better resolution of different chemical species) rather than the waves of classical polarography, and improve the detection limits, which in some cases can be as low as 10^-9 M.
234:
at the end of each drop lifetime (tast polarography). An even greater enhancement was the introduction of differential pulse polarography. Here, the current is measured before the beginning and before the end of short potential pulses. The latter are superimposed on the linear potential-time-function of the voltammetric scan. Typical amplitudes of these pulses range between 10 and 50 mV, whereas pulse duration is 20 to 50 ms. The difference between both current values is the analytical signal. This technique results in a 100 to 1000-fold improvement of the detection limit, because the capacitive component is effectively subtracted.
225:(the Hg drop) throughout the experiment. Because the potential changes during the drop lifetime (assuming typical experimental parameters of a 2 mV/s scan rate and a 4 s drop time, the potential can change by 8 mV from the beginning to the end of the drop), the charging of the interface (capacitive current) has a continuous contribution to the total current, even at the end of the drop when the surface area is not rapidly changing. As such, the typical signal to noise ratio of a polarographic experiment allows detection limits of only approximately 10 or 10 M.
213:
180:
148:, for which he won the Nobel prize in 1959. The main advantages of mercury as electrode material are as follows: 1) a large voltage window: ca. from +0.2 V to -1.8 V vs reversible hydrogen electrode (RHE). Hg electrode is particularly well-suited for studying electroreduction reactions. 2) very reproducible electrode surface, since mercury is liquid. 3) very easy cleaning of the electrode surface by making a new drop of mercury from a large Hg pool connected by a glass capillary.
167:
25:
233:
Dramatically better discrimination against the capacitive current can be obtained using the tast and pulse polarographic techniques. These have been developed with the introduction of analogue and digital electronic potentiostats. The first major improvement was obtained by measuring the current only
220:
There are limitations in particular for the classical polarography experiment for quantitative analytical measurements. Because the current is continuously measured during the growth of the Hg drop, there is a substantial contribution from capacitive current. As the Hg flows from the capillary end,
203:
of the working mercury drop electrode is linearly changed in time, and the electrode current is recorded at a certain time just before the mercury drop dislodges from a glass capillary from where the stream of mercury emerges. A plot of the current vs. potential in a polarography experiment shows
242:
Qualitative information can also be determined from the half-wave potential of the polarogram (the current vs. potential plot in a polarographic experiment). The value of the half-wave potential is related to the standard potential for the redox reaction being studied.
246:
This technique and especially the differential pulse anodic stripping voltammetry (DPASV) method can be used for environmental analysis, and especially for marine study for the characterisation of organic matter and metals interactions.
365:
492:
Nicholson, R. S.; Irving. Shain (1964-04-01). "Theory of
Stationary Electrode Polarography. Single Scan and Cyclic Methods Applied to Reversible, Irreversible, and Kinetic Systems".
170:
The number of publications (journal articles comprise ca. 42,000 out 45,468 , patent count is only 992) about polarography according to SciFinderN database on 2023-01-18.
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266:), which is the substance reduced or oxidized at the dropping mercury electrode. The Ilkovic equation has the form
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623:"Characterisation and modelling of marine dissolved organic matter interactions with major and trace cations"
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drop as a working electrode. In its most simple form polarography can be used to determine concentrations of
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until the 1990s (see figure below), when it was supplanted by other methods that did not require the use of
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Louis, Yoann; CĂ©dric
Garnier; Véronique Lenoble; Dario Omanović; Stéphane Mounier; Ivanka Pižeta (2009).
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Polarography is an electrochemical voltammetric technique that employs (dropping or static)
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Laboratory
Techniques in Electroanalytical Chemistry, Second Edition, Revised and Expanded
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The
Ilkovic equation is a relation used in polarography relating the diffusion current (
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Polarography played a major role as an experimental tool in the advancement of both
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136:(DME) or a static mercury drop electrode (SMDE), which are useful for their wide
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Reinmuth, W. H. (1961-11-01). "Theory of
Stationary Electrode Polarography".
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The equation is named after the scientist who derived it, the Slovak chemist
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is a constant which includes π and the density of mercury, and with the
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Skoog, Douglas A.; Donald M. West; F. James Holler (1995-08-25).
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is the number of electrons exchanged in the electrode reaction,
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360:{\displaystyle I_{\text{d}}=knD^{1/3}m_{r}^{2/3}t^{1/6}c}
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is the mass flow rate of Hg through the capillary (mg/s)
571:
Electrochemical
Methods: Fundamentals and Applications
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568:
275:
195:
species in liquids by measuring their mass-transport
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Kissinger, Peter; William R. Heineman (1996-01-23).
523:(7th ed.). Harcourt Brace College Publishers.
140:and renewable surfaces. It was invented in 1922 by
49:. Unsourced material may be challenged and removed.
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569:Bard, Allen J.; Larry R. Faulkner (2000-12-18).
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262:) and the concentration of the depolarizer (
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109:Learn how and when to remove this message
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423:is depolarizer concentration in mol/cm.
401:of the depolarizer in the medium (cm/s)
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521:Fundamentals of Analytical Chemistry
47:adding citations to reliable sources
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13:
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705:Adsorptive stripping voltammetry
594:Zoski, Cynthia G. (2007-02-07).
417:is the drop lifetime in seconds,
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642:10.1016/j.marenvres.2008.12.002
228:
216:HeyrovskĂ˝'s Polarograph and DME
34:needs additional citations for
957:Faraday's laws of electrolysis
841:Hanging mercury drop electrode
745:Differential pulse voltammetry
725:Cathodic stripping voltammetry
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446:Hanging mercury drop electrode
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780:Rotated electrode voltammetry
630:Marine Environmental Research
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876:Rotating ring-disk electrode
715:Anodic stripping voltammetry
597:Handbook of Electrochemistry
199:. In such an experiment the
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896:Standard hydrogen electrode
886:Saturated calomel electrode
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16:Method of chemical analysis
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821:Dropping mercury electrode
134:dropping mercury electrode
1004:Electroanalytical methods
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891:Silver chloride electrode
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691:Electroanalytical methods
765:Normal pulse voltammetry
760:Linear sweep voltammetry
441:Electroanalytical method
251:Quantitative information
871:Rotating disk electrode
846:Ion selective electrode
390:607 for average current
386:708 for maximal current
238:Qualitative information
183:HeyrovskĂ˝'s Polarograph
932:Butler–Volmer equation
785:Squarewave voltammetry
755:Hydrodynamic technique
710:Amperometric titration
384:has been evaluated at
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175:Principle of operation
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947:Debye–Hückel equation
790:Staircase voltammetry
573:(2 ed.). Wiley.
399:diffusion coefficient
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984:Analytical Chemistry
927:Activity coefficient
600:. Elsevier Science.
494:Analytical Chemistry
467:Analytical Chemistry
273:
153:Analytical Chemistry
43:improve this article
901:Ultramicroelectrode
866:Reference electrode
816:Auxiliary electrode
548:(2 ed.). CRC.
506:10.1021/ac60210a007
479:10.1021/ac60180a004
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851:Mercury coulometer
740:Cyclic voltammetry
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146:Jaroslav HeyrovskĂ˝
1009:Mercury (element)
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942:Cottrell equation
911:Working electrode
831:Electrolytic cell
750:Electrogravimetry
730:Chronoamperometry
720:Bulk electrolysis
607:978-0-444-51958-0
580:978-0-471-04372-0
555:978-0-8247-9445-3
530:978-0-03-005938-4
473:(12): 1793–1794.
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861:Potentiostat
770:Polarography
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122:Polarography
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41:Please help
36:verification
33:
881:Salt bridge
795:Voltammetry
208:Limitations
126:voltammetry
998:Categories
906:Voltameter
811:Amperostat
735:Coulometry
698:Techniques
452:References
128:where the
69:newspapers
826:Electrode
201:potential
99:June 2019
856:pH meter
650:19135243
435:See also
370:where:
144:chemist
397:is the
189:mercury
161:mercury
83:scholar
920:Theory
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