Dropping mercury electrode-technique for electrochemical analysis.

A dropping mercury electrode (DME) is a working electrode used in polarography, a technique for electrochemical analysis. It consists of a mercury reservoir and a capillary tube from which mercury drops continuously into the solution, providing a renewable and reproducible electrode surface.

1. Dropping Mercury Electrode Name- YASH L. PUROHIT Roll.No.-24-PCH-108 Subject-Physical Chemistry

2. Content INTRODUCTION CONSTRUCTION OF DME WORKING DISADVANTAGES APPLICATIONS

3. Introduction The dropping mercury electrode (DME) is a working electrode arrangement for polarography in which mercury continuously drops from a reservoir through a capillary tube into the solution . Types of mercury electrode : 1] DME(dropping mercury electrode) 2] SMDE (Static Mercury Drop Electrode) 3] HDME (Hanging Mercury drop electrode)

4. Construction of DME Mercury reservoir It consist of mercury reservoir bulb about 100 ml capacity . The reservoir is clamped in vertical position. It connected by flexible tubing to a glass capillary tube. The mercury reservoir is raised to appropriate height on the stand and it’s position is marked. The position/height of the reservoir should be kept the same throughout the experiment to get reproducible results (1 to 5 second).

5. Capillary tube The glass tube is 7 cm in length and 0.5 mm in diameter . One end of the capillary tube is attached to the flexible tube and clamped. The other end of the capillary tube dips under the surface of the solution to be analysed (electrode). The drops of mercury Come out from the capillary continuously . The drops of mercury are identical with dimeters of 0.5 to 1 mm . The life time of an individual drop is 3 to6 seconds. The DME is called as the working electrode or microelectrode or the indicator electrode .

6. Working Dropping mercury electrode is a polarization electrode and act as a both anode and cathode. The drop of mercury acts as counter electrode i.e. Anode if DME is cathode, cathode if DME is anode. The counter electrode(Pt) is non polarization electrode. The analyte solution, electrolyte like KCL is added i.e. 50-100 times of sample concentration.

7. Pure nitrogen gas is bubbled though the solution to expel out oxygen . The Gradually increasing voltage is applied to the polarographic cell and current is recorder . Graph is plotted between applied voltage and current , this graph is called as polarogram and the apparatus is known polarograph . The diffusion current produced is directly proportional to concentration of analyte and this is used for quantitative analysis.

8. Disadvantages of DME Capillary is very small and thus can be easily blocked . Mercury is very toxic . Surface area (0.50 to1 mm) of each drop of mercury is never constant .
It cannot be used at higher positive potential due to oxidation of mercury .

9. Applications of DME Electrochemical analysis : Metal ion detection (Cd²⁺, Pb²⁺, Zn²⁺). Pharmaceutical industry : Drug analysis. Environmental monitoring : Heavy metal detection. Industrial quality control .