The dependence of the formation of NH4+ and/or NO3- ions on chemical structure has been examined in TiO2 photocatalyzed oxidations of various amino acids, amides, and nitrogen-heterocyclic compounds. The primary amino groups and the amide moiety are converted photocatalytically and predominantly to NH4+ ions, whereas the hydroxylamino group in N-hydroxysuccinimide is photoconverted predominantly to NO3- ion. Results show that the nitrogen at the 1-position in imidazole is mainly photoconverted to NH4+ ion by analogy with the equivalent nitrogen atom in pyrrole; the nitrogen at the 3-position is transformed into NO3- ion. Formation of ammonium ions is faster than formation of nitrate ions in all but the N-hydroxysuccinimide substrate.