Universal Suitability and Sustainability Index (USSI): A Comprehensive Framework for Greener HPLC-UV/Vis Methods

A cornerstone in transforming a classical high-performance liquid chromatography (HPLC) ultraviolet/visible (UV/Vis) method into a greener and more sustainable one is considering the safety and toxicology of the solvent used in the method. The organic solvent used in the mobile phase may be replaced by a green solvent that is ideally bio-based and biodegradable to increase its greenness. However, the implementation of a new solvent for HPLC-UV/Vis requires the consideration of its environmental and health impacts, cost-effectiveness, user-friendliness, and impacts on the chromatographic method’s performance and its suitability. Existing greenness, blueness, and redness metrics expressing whiteness, aimed at evaluating the comprehensive sustainability of methods after solvent replacement, overlook the chromatographic suitability of the solvent; this may lead to suboptimal solvent replacement. In this work, the authors present a Universal Suitability and Sustainability Index (USSI), a sixteen-parameter scoring system that quantifies four main factors for the complete evaluation of a new solvent for implementation in HPLC. The four main factors are chromatographic suitability, greenness, blueness, and redness. The new index has been used to evaluate traditional liquid chromatographic as well as green solvent-based methods to give a universal overview to aid users, having significant effects on the weakness and strength aspects and making it easier to judge the suitability of a solvent and evaluate the overall method’s sustainability.