One of the first steps in a photosafety assessment is determination of the absorption spectrum of a test compound. A compound that absorbs sufficient light in the UV and visible light range will be a candidate for further photosafety testing. The amount of absorption is referred to as molar extinction coefficient (MEC). The MEC is used to determine if the compound requires additional evaluation. As described in OECD TG 432 and ICH Photostafety S10 documents, an MEC value > 1000 mol/L-1 cm-1 will be further evaluated for potential for phototoxicity. Testing is conducted under the guidance of OECD TG 101. Each test compound is evaluated at several concentrations under 3 different buffer conditions (acidic, neutral, or basic) to determine MEC.