Advanced Chromatographic Strategies for Assay, Purity, and Impurity Control in Pharmaceutical Drug Substances and Products

The assurance of pharmaceutical quality relies fundamentally on the ability to accurately quantify the active pharmaceutical ingredient (API) while simultaneously detecting and characterizing impurities at trace levels. Chromatographic techniques, particularly high-performance liquid chromatography (HPLC), remain the cornerstone of assay, purity, and impurity control in both drug substances and finished products. This review provides a comprehensive examination of advanced chromatographic strategies that address the evolving challenges in pharmaceutical analysis. We systematically discuss method development guided by Quality by Design (QbD) principles, emphasizing the selection of stationary phases, mobile phase optimization, and detectionmodalities including UV, charged aerosol, and mass spectrometry. Special attention is given to state-of-the-art approaches for impurity profiling: ultra-high performance liquid chromatography (UHPLC) for enhanced speed and resolution, two-dimensional liquid chromatography (2D-LC) for complex separation challenges, and supercritical fluid chromatography (SFC) as a sustainable alternative. The integration of high-resolution mass spectrometry (HRMS) for structural elucidation of unknown impurities is examined alongside regulatory expectations from ICH guidelines Q3A, Q3B, and M7. Forced degradation study design and stability-indicating method validation criteria are presented within the framework of ICH Q2(R2). Emerging innovations including artificial intelligence-assisted method development, green chromatography, and portable systems are critically evaluated. This review aims to serve as a practical resource for analytical scientists, regulatory affairs professionals, and quality control laboratories seeking to implement robust, efficient, and compliant chromatographic methods for pharmaceutical quality assessment.