An efficient method for fast elucidation of the electrochemical reactions of polycyclic aromatic hydrocarbons (PAH) has been set up by applying post-column electrochemistry in liquid chromatography-mass spectrometry (LC-MS). With this set-up strong improvement of sensitivity in the LC-MS analysis of PAH is observed. Due to their low redox potentials, the non-polar PAH are converted into the respective radical cations, which may further react with constituents of the mobile phase and in additional electrochemical oxidation steps. Among other products, mono-, di-, and trioxygenated species are observed in aqueous solutions, alkoxylated compounds in alcohols, and solvent adducts in the presence of acetonitrile. While more different products are observed by using atmospheric pressure chemical ionization in the positive-ion mode (APCI(+)), the deprotonation of hydroxylated species results in very clear spectra in the negative-ion mode (APCI(-)). Deuterated PAH and deuterated solvents were used to gain additional information on the formation of the reaction products.