In polarography with a dropping-mercury electrode, the flow that is controled by the rate of diffusion of the active solution species across the concentration gradient produced by the removal of ions or molecule at the electrode surface.

What is diffusion current in voltammetry?

In pulse voltammetry, the applied potential consists of a linear ramp with superimposed voltage pulses and the current is measured before and at the end of each pulse. ... Diffusion current is the difference between the limiting current and the residual current.

What is polarographic analysis?

polarography, also called polarographic analysis, or voltammetry, in analytic chemistry, an electrochemical method of analyzing solutions of reducible or oxidizable substances. ... Polarography is also used to identify numerous types of organic compounds and to study chemical equilibria and rates of reactions in solutions.

What is the function of polarographic electrode?

Introduction. Polarography is a voltammetric technique in which chemical species (ions or molecules) undergo oxidation (lose electrons) or reduction (gain electrons) at the surface of a dropping mercury electrode (DME) at an applied potential. Polarography only applies to the DME.

Where does the current observed in the polarography technique?

Here, the current is measured before the beginning and before the end of short potential pulses. The latter are superimposed to 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.

Explain: Residual Current, Diffusion current, Limiting current and Half Wave Potential.

32 related questions found

What is diffusion current in polarography?

[də′fyü·zhən ‚kər·ənt] (analytical chemistry) In polarography with a dropping-mercury electrode, the flow that is controled by the rate of diffusion of the active solution species across the concentration gradient produced by the removal of ions or molecule at the electrode surface.

Which equation is used for polarographic current?

Equation 4 is used widely in polarographic meas- urements and referred to as the Ilkovic equation. Relations between diffusion current and time have been investigated experimentally.

What is polarographic titration?

Amperometric titrations

The methods of polarography can be used to follow the progress of a titration that produces or consumes some electroactive species. The voltage applied to the working electrode is constant and sufficient to provide the diffusion-limited current for the observable analyte.

What is polarographic curve?

In direct current polarography (DCP) a constant potential is applied during the entire drop-life time. A current-voltage curve is constructed by applying a series of potential steps, each step being synchronized with the drop fall. ... The current is measured at the end of the drop life.

What is the full name of DME in polarographic cell assembly?

Dropping Mercury Electrode (DME):

Dropping mercury electrode (DME) is a working electrode arrangement for polarography in which mercury continuously drops from a reservoir through a capillary tube (internal diameter 0.03 - 0.05 mm) into the solution.

What are the conditions for performing polarographic determinations?

To conduct such an experiment, one requires at least two electrodes. The working electrode, which makes contact with the analyte, must apply the desired potential in a controlled way and facilitate the transfer of charge to and from the analyte. A second electrode acts as the other half of the cell.

How does oxygen interfere in polarographic analysis?

Oxygen is an electroreducible species its presence in solution produces a double wave in the range of 0 to - O2 +2H+ + 2e H2O2 H2O2 + 2H+ + 2e 2H2O This wave interferes with the analyte wave. Thus oxygen must be removed by bubbling nitrogen through the solution for five minutes to expel oxygen.

How does direct current polarography work?

Polarography uses potentiostatic control (Figure 1) of the working electrode polarized under conditions of convective diffusion; the current response i of the electrode system is measured depending on the polarizing voltage E whose time rate of change, dE/dt, is negligible with respect to the time constant of the mass ...

What causes diffusion current?

Diffusion current Density is a current in a semiconductor caused by the diffusion of charge carriers (holes and/or electrons). This is the current which is due to the transport of charges occurring because of non-uniform concentration of charged particles in a semiconductor.

What is diffusion current in analytical chemistry?

Diffusion current (i_d) is a current which is limited by the speed of particle diffusion in an electrolyte solution.

How can you prevent polarographic Maxima?

Maxima, frequently observed on polarographic waves due to the reduction or oxidation of cations, anions or neutral molecules thus interferring with analyte quantification, are usually suppressed by the addition of minute amounts of an appropriate surfacc-active agent.

What is mean by polarographic Maxima?

[pō¦lar·ə¦graf·ik ′mak·sə·məm] (analytical chemistry) A deceptively high voltage buildup on an electrode during polarographic analysis of an electrolyte; caused by a reduction or oxidation process at the electrode.

What is residual and diffusion current in polarography?

Reference electrode (Saturated calomel electrode) Auxillary electrode (Platinum electrode) Residual current is the slowly increasing current at the foot of the wave which is non faradaic in nature. The distance between the limiting diffusion plateau and the residual current is known as diffusion current (i_d).

What is DME in pharmaceutical analysis?

The dropping mercury electrode (DME) is a working electrode made of mercury and used in polarography. ... Like other working electrodes these electrodes are used in electrochemical studies using three electrode systems when investigating reaction mechanisms related to redox chemistry among other chemical phenomena.

Which indicator is used in Iodimetry and Iodometry?

The indicator that is usually chosen for titrations involving iodine (triiodide) is starch. Starch forms a dark blue complex with iodine. The end point in iodimetry corresponds to a sudden color change to blue. Likewise the end point in iodometry corresponds to a sudden loss of blue color due to the complex.

What is migration current?

[mī′grā·shən ‚kə·rənt] (physical chemistry) Additional current produced by electrostatic attraction of cations to the surface of a dropping electrode; an unpredictable and undesirable effect to be avoided during analytical voltammetry.

What is Amperometry used for?

Amperometry involves the measurements of currents at constant voltage applied at the dropping mercury electrode. The value of electrode potential is chosen in such a way that only the metal ion is reduced. This method is generally used for the determination of metal ion present in aqueous solution.

What is the meaning of limiting current?

The limiting current in electrochemistry is the limiting value of a faradaic current that is approached as the rate of charge transfer to an electrode is increased. The limiting current can be approached, for example, by increasing the electric potential or decreasing the rate of mass transfer to the electrode.

Which of the following are used to suppress the Maxima in polarography?

Gelatin has been used to suppress maxima in acid, alkaline (or ammoniacal) as well as in neutral media.