Amperometric determination of ammonium ions with a microbial sensor

A sensor for NH+4 ions has been developed, which consists of immobilized micro-organisms (Bacillus subtilis, Pseudomonas aeruginosa, Trichosporon cutaneum) in combination with an electrochemical transducer. This sensor is based on the measurement of acceleration of respiration after addition of NH+4 in the presence of glucose. The physiological background of this signal and its connection with NH+4 ion uptake and/or metabolism is discussed. The response time of the sensor is about 5-10 s for NH+4 ions. A linearity was observed between 0.005 and 0.15 mmol dm-3 NH+4 ions. The sensitivity of the sensor remained almost constant for 12 days. The sensor was used to determine NH+4 ions in a microbial fermentation broth.