An electrochemical sensor for measuring the amount of hydrogen sulphide or thiols in a fluid in a wellbore comprises a temperature- and pressure-resistant housing containing a flow path for the fluids. The fluids flow over one side of a gas permeable membrane made of zeolite or a suitable ceramic material,...http://www.google.de/patents/US7758734?utm_source=gb-gplus-sharePatent US7758734 - Methods and apparatus for the measurement of hydrogen sulphide and thiols in fluids
