On line mass spectrometric detection of ammonia oxidation products generated by polypyrrole based amperometric sensors

Polypyrrole (PPy) is the conducting polymer most widely employed in electrochemical sensors for ammonia detection in the last decade. Although sensors have been described in depth in the literature, the mechanism of ammonia detection by polypyrrole is still a matter of controversy. The differential electrochemical mass spectrometry (DEMS) technique, together with UV-Vis spectroscopy, gives direct and conclusive evidence with respect to the ammonia oxidation products formed in NaOH solution (pH = 10) at polyrrole or N-methyl polypyrrole film sensors polarized at 0.35 V (Ag/AgCl). Monitoring of the different possible ammonia oxidation products by on-line DEMS measurements indicates that only NO is formed and that other species such as N-2 or N2O are absent. UV-Vis absorption spectroscopy also showed that ionic products such as nitrate or nitrite are not formed. (C) 2003 Elsevier B.V. All rights reserved.