Esterification of Ibuprofen in Soft Gelatin Capsules Formulations—Identification, Synthesis and Liquid Chromatography Separation of the Degradation Products

Abstract Unknown impurities were identified in ibuprofen (IBU) soft gelatin capsules (SGCs) during long-term stability testing by a UHPLC method with UV detection and its chemical formula was determined using high resolution/accurate mass (HRAM) LC–MS. Reference standards of the impurities were subsequently synthesized, isolated by semi-preparative HPLC and characterized using HRAM LC–MS, NMR and IR. Two impurities were formed by esterification of IBU with polyethylene glycol (PEG), which is used as a fill of the SGCs, and were identified as IBU–PEG monoester and IBU–PEG diester. Two other degradants arised from reaction of IBU with sorbitol and sorbitan, which are components of the shell and serves as plasticizers. Thus, IBU sorbitol monoester (IBU–sorbitol) and IBU sorbitan monoester (IBU–sorbitan ester) were identified. An UHPLC method was further optimized in order to separate, selectively detect and quantify the degradation products in IBU SGCs.