Voltammetry

basics of linear sweep, differential and normal pulse voltammetry. check out the 10th slide in full view.

1. Voltammetry and polarography 1. Normal Pulse voltammetry 2. DIFFERENTIAL Pulse voltammetry By Shobana.N.S Queen Mary’s College, Chennai

2. Voltammetry It is an Electro- analytical technique. It gives information about the analyte . We can even measure the amount of current by varying the voltage . The change in current with the varying voltage gives the plot and is known as uoltammogram There is a minimum potential required to initiate an oxidation or reduction reaction at an electrode.

3. Instrumentation It is a three electrode system. 1. Working electrode ; 2. Reference electrode and 3. Auxiliary electrode. working electrode; (2) auxiliary electrode; (3) reference electrode

4. Working Electrode Ranges from small mercury drop to flat platinum disc. Platinum disc DME

5. Other commonly used electrode materials gold, platinum and glassy carbon. Glassy carbon Gold electrode

6. Depending on the choice of working electrode, the type of voltammetry is decided. Example : We use Dropping Mercury Electrode (DME) in Polarography technique We use Platinum electrode in Cyclic Voltammetry We use Glassy Carbon as electrode in Linear Sweep Voltammetry .

7. Reference Electrode Usually Standard electrode is used as Reference electrode. Its potential is constant . It provides potential to the Working electrode. Common reference electrode are : Calomel electrode and Ag/ AgCl electrode

8. Auxiliary Electrode It is usually a thin platinum wire. It serves merely to carry the current flowing through the cell. Usually redox reaction occur simultaneously at the auxiliary electrode.

9. Type of Voltammetry LINEAR SWEEP VOLTAMMETRY STAIRCASE VOLTAMMETRY CYCLIC VOLTAMMETRY SQUAREWAVE VOLTAMMETRY ANODIC STRIPPING VOLTAMMETRY CATHODIC STRIPPING VOLTAMMETRY ABSORPTIVE STRIPPING VOLTAMMETRY ALTERNATING CURRENT VOLTAMMETRY POLAROGRAPHY ROTATED ELECTRODE VOLTAMMETRY NORMAL PULSE VOLTAMMETRY DIFFERENTIAL PULSE VOLTAMMETRY CHRONOAMPEROMETRY.

10. Linear Sweep Voltammetry In linear sweep voltammetry (LSV) a fixed potential range. the voltage is scanned from a lower limit to an upper limit.

11. In LSV measurements the current response is plotted as a function of voltage rather than time. The scan begins from the left hand side of the current/voltage plot where no current flows. As the voltage is swept further to the right (to more reductive values) a current begins to flow and eventually reaches a peak before dropping

12. Normal Pulse Voltammetry Normal polarography has been replaced by various forms of pulse polarography. It uses a series of potential pulses . Here the pulse time ( tp ) is 50ms . Each potential has different amplitude

13. Differential Pulse Voltammetry If potential pulse is applied periodically to the Linear Sweep Voltammetry , then it is known as Differential Pulse Polarography. Hence it is denoted as the differential of linear sweep voltammetry .

14. The current is measured twice per cycle. Here the pulse time ( tp ) is 17ms. The difference in the two currents gives rise to the peak-shaped voltammogram . consistent enhancement of the signal is achieved. Detection limit is as low as 10 -8 M Each potential step has the same amplitude

15. Polarography Polarography is the branch of voltammetry in which a dropping mercury electrode (DME) is used as the working electrode.

16. Conventional DC Wide cathodic potential range and a renewable surface Hence widely used for the determination of many reducible species Reduction begins at sufficiently negative potential voltage applied to the polarisable electrode is increased over the range of 0-2V It is known as incomplete electrolysis .

17. Jaroslav Heyrovsky He was the inventor of Polarographic technique. He received Nobel Prize in 1959 He is known as father of electro analytical method .

18. Polarography has a special characteristic : Use of polarized electrode. Use of depolarized electrode. POLARIZED ELECTRODE : DME DEPOLARIZED ELECTRODE : SCE

19. Dropping Mercury Electrode It is the working electrode in one of the voltammetry technique known as polarography

20. Advantages of DME Clean Surface generated Rapid constant current achievement Even metal with high negative standard voltage systems can be studied without hydrogen. Amalgam formation more favourable.

21. THANK YOU !!