Miniature ammonia sensor which detects ammonia in three steps

Dutch researcher Björn Timmer has developed a miniature ammonia sensor which detects ammonia in three steps. The sensor uses very small quantities of a reagent and is cheap to use. It might find a use in hospitals for detecting stomach ulcers, and in pig stalls and poultry farms for measuring the ammonia concentration in the air.

Existing sensors for measuring ammonia are as large as a removal box and very expensive. However, a better alternative is now available. Electrical engineer Timmer, from the University of Twente, scaled down the ammonia-detecting apparatus to the size of a chip.

First of all the gaseous ammonia comes into contact with an acid solution which binds the ammonia to the water. A pump then transports the solution to a separating section. This consists of two channels, with in between a permeable membrane. This part adds an alkaline fluid so that the acidifying gases are bound to the water and can no longer pass through the membrane. In the solution formed, the ammonia is in a gaseous form.

The ammonia passes through the membrane into the second channel, through which a purified stream of water is pumped that transports the ammonia with it. Finally, a conductivity sensor measures the concentration of ammonia ions in the stream of water. The new sensor measures an ammonia concentration of one-part ammonia in one billion parts of air.

In hospitals it might be possible to use the miniature sensor to detect stomach ulcers. Too much ammonia in expired air is indicative of bacterial infections in the stomach, such as stomach ulcers. With the sensor these can be detected at an early stage.

The government is also interested in the sensor. The measuring technique has been developed at the Energy Research Centre of the Netherlands. With low purchase and service costs the government can, for example, hang up cheap measuring sensors to better chart the greenhouse effect. Another application lies in the stalls of pig and poultry farms. There, ammonia fumes are released from the manure. If the sensor can measure these concentrations, it will be possible for the farmer to specifically control the ventilation so as to maintain a healthy stall climate. The company R & R Mechatronics is investigating the feasibility of producing the chip.

The research was funded by the Technology Foundation STW.

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