The increase in ammonia and ethanol in the exhaled breath stream following mouthwashes by aqueous solutions of urea and sugar (sucrose), respectively, has been investigated by analysing exhaled breath in real time using selected ion flow tube mass spectrometry, SIFT-MS. It is shown that the measured levels of these compounds in the stream of exhaled breath can be much greater than the endogenous levels originating at the alveolar boundary. Thus, it is concluded that without careful preparation, mouth production of these compounds, and other compounds as yet unidentified, can seriously compromise the quantification of truly endogenous trace compounds present in blood and in the alveolar breath, as required for clinical diagnosis, and can probably introduce additional compounds into the breath stream that could seriously mislead breath analysis. The concentrations of both the urea and sucrose solutions used to enhance the ammonia and ethanol levels were larger than normally present in food and drinks and so in most situations such severe enhancements will not occur.

J Heyrovský Institute of Physical Chemistry Academy of Sciences of the Czech Republic Dolejskova 3 182 23 Prague 8 Czech Republic

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