Analytical approach for conversion of conventional to green RP-HPLC methods for analysis of lipophilic neutral and...

Conventional RP-HPLC methods in pharmaceutical industry still dominantly rely on hazardous solvents like methanol (MeOH) and acetonitrile (ACN), presenting significant environmental and safety challenges. Although ethanol (EtOH) is recognized as greener alternative, isoeluotropic relationships between EtOH and these conventional solvents will broaden its implementation in routine HPLC analyses. To address this issue, the study presents an empirical approach using volu-metric fraction (φ) equivalence to establish initial chromatographic conditions, enabling predictable substitution of MeOH and ACN with EtOH in the LC mobile phase without altering other chromatographic parameters. The approach was established using adsorption (log-log) retention model across multiple C₁₈ stationary phases, applicable for lipophilic neutral and basic active pharmaceutical ingredients (APIs). For neutral APIs, φ MeOH ≈ 1.6 φ EtOH and φ ACN ≈ 1.1 φ EtOH, while for basic APIs φ MeOH ≈ 1.5 φ EtOH and φ ACN ≈ 1.0 φ EtOH. The general applicability was confirmed under isocratic conditions by successfully converting conventional RP-HPLC methods for an independent set of APIs into green, EtOH-based alternatives. Notably, this work extends previous research focused on lipophilic acidic to neutral and basic APIs, broadening its utility for the most widely used APIs in the pharmaceutical industry. The proposed framework supports sustainable analytical practices and improves laboratory safety without extensive method redevelopment.