Dropping Mercury Electrode (DME)

• The Dropping Mercury Electrode (DME) is commonly used in polarography and electrochemical techniques.
• It provides a clean, renewable surface for redox reactions, offering low background current and reproducibility.

Construction of Dropping Mercury Electrode:

1. Capillary Tube:

   • A fine glass tube with an internal diameter of 10-50 µm through which mercury flows. The tube is mounted vertically and connected to a mercury reservoir.

2. Mercury Reservoir:

   • Holds the mercury supply and controls its flow into the capillary by adjusting the reservoir height or using a pressure regulator.

3. Electrode Holder:

   • A supportive structure that holds the capillary tube and provides electrical connection to the mercury. It is typically made from insulating material.

4. Electrical Connection:

   • A conductive wire establishes contact between the mercury in the capillary and the potentiostat.

Working of Dropping Mercury Electrode:

1. Mercury Flow:

   • Mercury flows through the capillary by gravity or controlled pressure, forming droplets at the tip.

2. Droplet Formation:

   • The mercury droplet grows due to surface tension until it reaches a critical size and detaches.

3. Droplet Detachment:

   • Detachment occurs periodically (1-20 drops per second), ensuring a fresh, renewable surface for the next drop.

4. Electrochemical Measurement:

   • During droplet formation and detachment, the potentiostat applies potential, enabling redox reactions of the analyte at the mercury surface, generating a measurable current.

5. Renewable Surface:

   • Each droplet detachment creates a new clean surface, minimizing contamination and fouling.

Advantages:

• Clean, reproducible surface.
• Low background current.
• Suitable for studying a wide range of redox reactions.

Limitations:

• Mercury toxicity.
• Limited potential range due to mercury oxidation/reduction.

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