E.V. Stepanov, P.V. Zyrianov

Ammonia (NH3) is one of the end products of nitrogen metabolism. It-s production takes place practically in all human organs and tissues. Amino acids, amines, amine groups in proteins are the main sources of NH3 in organism. Tens of different enzymatic systems take part in ammonium production. In spite of the high intensity of these processes the ammonium content in blood and tissues is not high because of processes of NH3 bounding and elimination with urine, sweat and exhaled air. The urea production in liver is the main such process of elimination. The NH3 content in organs and tissues is defined by the intensities ratio for these processes and depends on the energy metabolism, acid-base balance, protein catabolism and hormone regulation. The NH3 con-tent in exhaled air could reflect ammonium content in venous blood and then could serve for es-timation of the organism ammonium state and factors of its variation. Dynamic and mechanisms of NH3 excretion with exhaled air for healthy person and in pathologies are not well studied now because of difficulties of its accurate quantitative analysis in breath. At the same time the data on NH3 excretion with breath could be useful for the purpose of clinical diagnostics including neph-rology, hepatology, toxicology, pulmonology, as well as for diagnostics in hyperbaric physiology and sport medicine. And this defines the development of high sensitive and selective technique for ammonia detection in exhaled air is topical. In frames of the present study a selection of spectral regions best for the ammonia detection in exhaled air was provided. For this purpose rotational-vibration spectra of NH3, CO2 and H2O in the middle IR spectral region near 10 micron were calculated and analyzed. The best spectral regions were found to be located near 967 and 1067 cm-1. An adaptation of optical schematic of gas analyzer based on tunable diode lasers was provided. Electrical, thermal and spectral properties of tunable diode laser operated in this spectral region and used for the ammonia detection were carefully studied. To increase the detection sensitivity of the spectral analysis two channel optical scheme and multipass gas cell with optical path of 15 m were used. Special algorithms of spectral data filtering and processing as well as noise suppression were applied to minimize systematic and random errors of NH3 concentration analysis in breath and to provide this measurements in real time regime. The applied optical schematics and electronic solutions have provided the analytical parameters of the system necessary for quantitative analysis of NH3 content in exhaled air. Particularly, the concentration sensitivity was at the level of 0.1 ppb, accuracy - 3-5%, selectivity to CO2 and H2O - close to 100%, speed of the analysis - 3-10 s, volume of gas sample - 0.5-1.0 l. Special protocols of endogenous NH3 studies in human breath were developed including order of respiration maneuvers and analysis conditions. Variations of ammonia content in exhaled air of healthy persons were studied. The normal level of NH3 content in breath was measured to be in the region of 150-200 ppb and could increase 2-3 times as much for smoking persons.