I have to analyze 5-fluorouracil and its impurities (5-methoxyuracil, barbituric acid and urea) by the HILIC method with a UV detector. But what I don't understand is how to choose the detection wavelength, 5-Fluorouracil, 5-Methoxyuracil and Barbituric acid absorb at around 265 nm. Urea is a molecule that is analyzed at 200nm because it does not absorb on higher wavelengths. As I have to analyze them by the same method, I don't understand which wavelength should I choose ? Should I choose the urea wavelength or choose a wavelength that is between 200 and 265 nm ?