Electrochemical method of determining oxygen, halothane and nitrous oxide

A method of electrochemically sensing the presence of oxygen and nitrous oxide and halothane in a fluid comprises exposing a gold or platinum electrode and a silver electrode to the fluid through permeable means and an electrode-contacting electrolyte through which gases from the fluid can pass,

• holding the gold or platinum electrode at a first potential such that oxygen is reduced at that electrode and sensing any first current flowing through the gold or platinum electrode;
• holding the silver electrode at said first potential such that oxygen and halothane are reduced at that electrode and sensing any second current flowing through the silver electrode;
• subsequently holding the silver electrode at a potential such that oxygen and halothane and nitrous oxide are reduced at that electrode and sensing any third current flowing through the silver electrode;
• and from the three currents determining whether any of the three gases are present.