Nondestructive near‐infrared analysis of intact tablets for determination of degradation products

Near‐infrared spectrometry was used in this study to examine intact aspirin tablets in order to demonstrate the usefulness of the technique as a nondestructive method of quality control. Unique sampling optics were used to simultaneously illuminate the entire surface of the tablets, including the top, bottom, and side. Changes in individual tablet spectra were correlated to (a) the time that the tablets spent in a hydrator, (b) the mass of water absorbed by the tablets, and (c) the mass of salicylic acid formed by base‐catalyzed hydrolysis of acetylsalicylic acid. A prediction equation for each of these three parameters was constructed using near‐infrared spectral reflectance values obtained from intact tablets. Prediction errors were low for (a) the time that tablets spent in the hydrator (± 19 h over a period of 168 h), (b) the mass of water absorbed (±0.04% of tablet mass), and (c) the mass of salicylic acid formed (±0.04% of tablet mass).