Abstract: The present disclosure generally relates to methods of measuring benzimidazole-based corrosion inhibitors in cooling water. Methods may include withdrawing a sample of water containing a benzimidazole-based compound from an aqueous system and adding an acid to the sample of water and/or diluting with water. Methods may also include exposing the sample of water to light energy of a selected excitation wavelength and measuring an intensity of emitted light about a selected fluorescence emission wavelength. The intensity of the emitted light may be compared to a standard curve, which can be a plot of fluorescence emission intensity of the benzimidazole-based compound versus concentration of the benzimidazole-based compound. The concentration of the benzimidazole-based compound in the sample of water may be determined from the standard curve.