Related Experiment Video
Updated: Apr 26, 2026

Fast and Accurate Exhaled Breath Ammonia Measurement
Published on: June 11, 2014
The origin of mouth-exhaled ammonia
W Chen1, M Metsälä, O Vaittinen
1Laboratory of Physical Chemistry, Department of Chemistry, PO Box 55 (A. I. Virtasen aukio 1), FI-00014 University of Helsinki, Finland.
Abstract:
It is known that the oral cavity is a production site for mouth-exhaled NH3. However, the mechanism of NH3 production in the oral cavity has been unclear. Since bacterial urease in the oral cavity has been found to produce ammonia from oral fluid urea, we hypothesize that oral fluid urea is the origin of mouth-exhaled NH3. Our results show that under certain conditions a strong correlation exists between oral fluid urea and oral fluid ammonia (NH4(+)+NH3) (rs = 0.77, p < 0.001). We also observe a strong correlation between oral fluid NH3 and mouth-exhaled NH3 (rs = 0.81, p < 0.001). We conclude that three main factors affect the mouth-exhaled NH3 concentration: urea concentration, urease activity and oral fluid pH. Bacterial urease catalyses the hydrolysis of oral fluid urea to ammonia (NH4(+)+NH3). Oral fluid ammonia (NH4(+)+NH3) and pH determine the concentration of oral fluid NH3, which evaporates from oral fluid into gas phase and turns to mouth-exhaled NH3.
Related Concept Videos
Overview of Nitrogen Metabolism
The largest pool of nitrogen available in the terrestrial ecosystem is gaseous nitrogen (N2) from the air, but this...
Inorganic Nitrogen Assimilation
Preparation of Amines: Alkylation of Ammonia and Amines
Each alkylation step makes the nitrogen center more nucleophilic, which triggers successive alkylations until a quaternary ammonium salt is formed. Considering...
Comparative Excretory Systems
Preparation of 1° Amines: Gabriel Synthesis
Strong bases like NaOH or KOH deprotonate the phthalimide to form the corresponding anion, which acts as a nucleophile. Further, the anion attacks an...
Urea Cycle

