Application of online liquid chromatography/quadrupole time‐of‐flight electrospray ionization tandem mass spectrometry for structural characterization of linagliptin degradation products and related impurities

Rationale Linagliptin is a drug used for the management of type 2 diabetes, which is a leading cause of global ill health and mortality. Impurities can affect the quality and safety of drug products and eventually may affect human health. A robust, sensitive and reliable analytical method is required to detect, characterize, quantify and control the presence of impurities in finished pharmaceutical products such as linagliptin. Methods Linagliptin was stressed under harsh conditions as in the ICH Q1A (R2) guidelines to generate degradation products. The degradation products and process‐related impurities were separated using an InertSustain C8 column (4.6 mm × 150 mm, 5 μm) and characterized by tandem quadrupole time‐of‐flight mass spectrometry in positive mode electrospray ionization. The developed method was validated according to the ICH Q2 (R1) guidelines. Results Upon forced degradation, 12 degradation products were obtained (6 in oxidative stress and 3 in each of acid and alkaline hydrolysis). The special finding here was the presence of a pair of isomeric degradation products in acid hydrolysis and the formation of degradation products in base hydrolysis and oxidative degradation caused by the use of acetonitrile as a diluent. The 12 degradation products and 6 process‐related substances were successfully identified using liquid chromatography/tandem mass spectrometry. Conclusions A reversed‐phase high‐performance liquid chromatography method was developed and validated for the separation of the 12 degradation products and 6 process‐related impurities. Structural characterization of all impurities was carried out using fragmentation pathways obtained from tandem mass spectrometry. The method was sufficiently sensitive and reproducible for quality control of linagliptin and for further research studies.