Aspirin, also known under the pharmaceutical name acetylsalicylic acid, is one of the most widely used types of nonsteroidal anti-inflammatory drugs, being able to combat not only mild and moderate pain, found at several levels of the body, but also to reduce fever (antipyretic effect).

In this article, we determined the chemical composition of aspirin by IR spectroscopy using the SHIMADZU FT–IR spectrometer for wavelengths between 4000–400 cm^-1. The wavelength range in which absorption bands appear is between 4000cm-1 and 400 cm^-1. Aspirin contains the following functional groups: C-H, C-OH, CH₃, C=O, C=C, P-OH, CO₂.