The oxidation behavior of L-tyrosine was studied using a carbon-based screen-printed electrode in ammonium acetate buffer, coupled with an electrochemical flow cell and mass spectrometry via capillary electrophoresis. Cyclic voltammetry and linear sweep voltammetry were employed to investigate the oxidation behavior of this compound. The migration in capillary electrophoresis, mass-to-charge ratios, and isotopic patterns of L-tyrosine's oxidation products were examined. Results indicated that three different diffusive oxidation products could be detected within a potential range of 0–1.3 V. Because measurements are made over a short time, both stable oxidation products and intermediates could be observed. Three main product species were recorded with real-time electrochemistry-mass spectrometry and electrochemistry coupled to capillary electrophoresis-mass spectrometry. The product species 3-nitrotyrisine was identified with the help of an available standard, and the formulas of the other two product species were determined, along with suggestions corresponding to structures.