Ammonia nitrogen measurement system based on miniaturized ammonia sensing unit

An amperometric ammonia microsensor based on the thin liquid layer in micro-pool has been designed and prepared. An ammonia nitrogen measurement system utilizing such a microsensor has been constructed. The ammonia nitrogen measurement method using an amperometric ammonia microsensor was investigated. The microsensor is a microelectrode chip fabricated with MEMS technology. The thin electrolyte layer and the reservoir for electrolyte are combined, thus the reservoir is eliminated and the sensor size is reduced. Platinum black is chosen as the sensing material, which is electrodeposited on the bare microelectrodes using electrochemical method. LiCl solution, which is one kind of hygroscopic electrolyte, is chosen as the thin liquid layer. Measurements of ammonia nitrogen samples with various concentrations using the self-designed measurement system were carried out. A linear calibration curve between 0.4~5 mg/L with the correlation coefficient of 0.992 was obtained. A detection limit of 0.2 mg/L was achieved. The 90% response time was within 2 minutes. Measurement results reveal that the proposed ammonia nitrogen measurement method using the amperometric ammonia microsensor is feasible. The design of the thin liquid layer in micro-pool simplifies the structure and facilitates the fabrication process. Meanwhile, the thin layer of electrolyte reduces the time for ammonia to diffuse to the microelectrodes, thus a fast response time is achieved.