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Recent developments aiming to microsensors based on floating gate field effect transistors (FGFET) were investigated for application in a rodent cage monitoring. Given that these sensors were on the forefront of technology, a theoretical model was developed for the ammonia sensor to further understand the chemical reaction taking place on its surface. The sensors were tested in a controlled environment, where the air quality was known. The magnitude and time of the response to different levels of ammonia were determined in the 50-100 ppm range. The reaction mechanism selected for the model which was best supported by the literature and the experiments was molecular adsorption of ammonia on a titanium nitride surface. The experimental results were fitted to the model to obtain the adsorption and desorption rate constants, the equilibrium concentration constant, equilibrium constant, and Gibb's free energy, which were 6.28 L/mol · s, 6.43 × 10-3 s-1, 976.7 L/mol, 39.04, and -9.25 kJ/mol, respectively. Based on these values, it was determined that the forward reaction, or adsorption, occurs spontaneously. There was good correlation between the theoretical model and the experimental results, indicating that the theoretical model was sufficient for this application.