Investigations On A Miniaturized Ammonia Detection System

Gaseous ammonia is colorless and irritating, which has significant impact on environment as well as human health. However, in the field of clinical diagnosis, the levels of ammonia in the exhaled breath can be used to indirectly evaluate the effect of hemodialysis of the patients with renal failure, which provides an effective technical means for the diagnosis of disease and assessment of clinical application. Nowadays, the routine methodology for ammonia determination includes Mass Spectrometry, which usually needs bulky instruments. With the rising analytical requirements for field detection, bulky instruments are apparently unable to meet the demands. The miniaturization of analytical instruments for specific analytical purposes has been one of the most important analytical tasks.The present work is based on the national standard method, i.e, sodium hypochlorite-salicylic acid spectrophotometric method. A polypropylene film tube is employed as the flow cell. The detection unit consists of halogen light source, filters, optical fibers, flow cell, photoelectric conversion system and data acquisition card. The visible light (emission wavelength 360 nm-700 nm) generated by halogen lamp will pass the filters (700 nm). The filtered light is transmitted through the optical fiber, absorbed by the samples in the flow cells and then detected by the photodiode. The volume of flow cell which is made of polytetrafluoroethylene tube is 150μL (id.2 mm). Using DI water as carrier, the pre-reacted sample is introduced into the detection system by the peristaltic pump via the six-port inject valve. The sample signal is calculated through the difference between the absorbance of sample and blank. The experiment was divided into sample injection and detection units. A serious of conditions is optimized. Under the optimal experimental conditions, the detection limit of 10.8μg L-1 (n=9) and the linear range of 50-700μg L-1,along with a RSD value of 2.1%(n= 9) are achieved with the sample volume of 50μL. In order to validate the stability of the system, the calibration curve is investigated in five consecutive days and a satisfactory result is obtained. The reliability of the present system is verified by recoveries of ammonia in snow water. The present system is also used for gaseous ammonia in air. Polypropylene film tube is used as a novel gas absorber for developing the on-line detection for gaseous ammonia. Hope to achieve online testing for trace amounts of ammonia in exhaled breath. Although the preliminary result is obtained, further research needs to be carried out.