Flow injection amperometric detection of ammonia using a polypyrrole-modified electrode and its application in urea and creatinine biosensors

The interaction of unprotonated ammonia molecules with polypyrrole (PPy) is employed for the amperometric detection of ammonia with the use of an anodically polarized platinum electrode modified with PPy as the working electrode. The polymer was obtained by electropolymerization in potentiostatic conditions from aqueous solutions. Chloride was found to be the most suitable dopant for PPy from several dopants studied. Satisfactory dynamic characteristics of detection permit its application to the determination of ammonia in a flow injection system up to 100 mu M of analyte with a detection limit of 0.6 mu M. Such a detector of ammonia was also employed as the internal detector in amperometric biosensors for urea and creatinine by the immoblization in a different way at the PPy surface of urease and creatinine iminohydrolase, respectively. An amperometric biosensor of very low sensitivity was obtained by urease entrapment in the PPy layer during the electropolymerization. The urea membrane biosensor was successfully applied in the determination of urea in human blood samples. On the basis of results of elemental analysis, UV and IR spectroscopy some suggestions are presented about the mechanism of the interaction between PPy and ammonia and about the anodic electrode process occurring in the amperometric detection of ammonia.