Ibuprofen is an example of a nonsteroidal anti-inflammatory drug (NSAID) and is widely used as an antipyretic or analgesic agent. It has been reported that during tests to confirm stability during storage, decomposition products were generated due to temperature, acidity, light irradiation, etc. of the surroundings. In particular, the area percentage of 4-isobutylacetophenone, one of the decomposition products, increased by about 40% after the 72-hour light irradiation test. The Nexera Series photodiode array detector SPD-M40 is equipped with a UV cut-off filter that exlcudes light in the ultraviolet range, in order to ensure more stable detection of compounds that are prone to photodegradation. We are introducing examples of improving the quantitation of ibuprofen using the UV cut-off filter function of the SPD-M40.