Abstract: In my master thesis I investigated the Fenton reaction and a similar reaction with Fe(III) salt. I found out that the salt in contrast to the hydrogen peroxide has a greater influence on the decomposition of the organic matter itself. The classical Fenton reaction using Fe2+ ions is more efficient in decomposition than the Fenton-like reaction with existing Fe3+ ions. Higher concentrations of the divalent salt led to a stronger decomposition of the analytes investigated. Cl- ions represent traps of hydroxyl radicals. I demonstrated their interference effect by adding different concentrations of KCl salt to the experimental mixture for the Fenton reaction. In the case of caffeine decomposition, the addition of anions had no effect on the extent of degradation, whereas the opposite effect occurred with theophylline. I tried to determine the order of the reaction, but it turned out that the reaction is of a non-integer order. The decomposition reaction is most effective in the acidic range at pH = 3, and during decomposition I could not detect any compounds that would absorb light with wavelengths up to 230 nm, where acetic acid cut off. No decomposition products could be determined in the mass spectra of the final solution either. Finally I determined the conditions for a 100% decomposition. These are: pH = 3, (H2O2) = 100 μmol/L in c(Fe2+) = 100 μmol/L
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