A receptacle connector mounted to the printed circuit board, includes an insulative housing defining a mating tongue and a metallic shell enclosing the housing to form a mating cavity in which said mating tongue forwardly extends. The potential of the working electrode is pulsed and measuring phases and relaxation phases are alternately produced, the pulse lengths of the measuring phase and relaxation phase being predetermined in a suitable manner. An electrical voltage is applied between the first and second electrodes, and a change in an electrical variable is measured between the first and second electrodes when ammonia is present. Moreover, movement of the cutting-pushing element backwards, away from the nozzle, by release of the force transmitting element, allows at least one tooth to engage and pull the container backwards into the housing.