Abstract: An electrochemical cell has an electrolyte container 4 with a wall 5, apertured to let electrolyte soak a membrane 5b. A thin wire loop electrode 13 of (if necessary) precisely known length and cross-section rests on the membrane and contacts a metallised portion 21a of the membrane electrode 21, itself contacting the air through a sinter 22. The loop electrode 13 is sealed into its electrolyte chamber between 21a and 5b by an O-ring 15.If the electrolyte is acetonitrile, then methane in the air can be detected.

Abstract: A method of testing a body of fluid for the presence of at least one component in which a measuring means is exposed successively to two masses of fluid derived from the body of fluid, the two masses differing in respect of the concentration of an active component to which the measuring means is sensitive by an amount dependent upon the concentration in the body of fluid of the at least one component to be detected, the measuring means being exposed to at least one of the two masses of fluid for a time sufficient for the measuring means to reach a known proportion less than one hundred percent of its equilibrium state with the active component in the fluid to which the measuring means is exposed. The two masses may be derived from the same sample or from different samples of the body of fluid.