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

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

1) Mercury flow

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

2) Droplet formation and growth

• 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.