Ultraviolet spectrophotometry can help determined the quantity of paracetamol and acesulfam-K when mixed. The isosbestic wavelength (lambda iso) and the absorbency at the wavelength (Aiso) determined with equimolecular solutions or by annulation of the first derivative at 226 nm for paracetamol determination and at 242.5 nm for acesulfam-K determination can be used.