Patent ID: 8268146

Claim:
A wellbore tool comprising an electrochemical sensor for measuring the amount of hydrogen sulphide or thiols in a fluid, the sensor comprising: a housing having a flow path for the fluid therethrough, a gas permeable membrane disposed in the housing and having one side exposed to the flow path, a chamber disposed in the housing, the chamber being exposed to the other side of the membrane and containing reagents which together with the hydrogen sulphide or thiols entering the chamber via the membrane create a redox reaction resulting in an electrical current dependent upon the amount of hydrogen sulphide or thiols in said fluid, and at least two electrodes in the chamber which is exposed to the other side of the membrane, said electrodes being a working electrode and a counter electrode spaced from each other and both exposed to the reagents in the chamber, the well bore tool also comprising means for drawing in fluid and passing it along the said flow path, and electronic circuitry connected to the electrodes in the chamber, operable to apply repeatedly varying potential to the working electrode and measure the peak current flowing between the working electrode and the counter electrode.