Universal Suitability and Sustainability Index (USSI): A Comprehensive Framework for Greener Chromatographic Methods

A cornerstone in transferring a classical Liquid Chromatography (LC) with UltraViolet/Visible (UV/Vis) detector into a greener and, beyond, towards a sustainable analytical method should consider the safety and health of the used organic solvent in the method. Toxic organic solvent portions used in the mobile phase can be replaced by an eco-friendly green solvent that is ideally bio-based and biodegradable to increase the greenness index of the method. However, the implementation of a new organic solvent for High Performance Liquid Chromatography (HPLC-UV/Vis) and/or UltraHigh Performance Liquid Chromatography (UHPLC-UV/Vis) requires not only a simple consideration of its environmental and health impact, cost-effectiveness, user-friendliness, and impact on the analytical performance of the method but rather a systematic evaluation of its chromatographic suitability. Existing greenness, blueness, and redness metrics expressing whiteness for evaluating the sustainability of liquid chromatographic methods after solvent replacement overlook the chromatographic suitability of the selected green solvent, potentially leading to suboptimal solvent replacement and an incomplete view of its capabilities. In this work, the authors present a Universal Suitability and Sustainability Index (USSI), a sixteen-parameter scoring system that quantifies four main factors for complete evaluation of a new solvent for implementation in liquid chromatography. This index is even beyond the white analytical chemistry principle. The four main factors are chromatographic suitability, greenness, blueness, and redness. Three of these factors, namely greenness, blueness, and redness, are based on available tools and metrics to evaluate the environmental and health, impact on the practicability, and the analytical performance of the method. The fourth factor is added as an important criterion to judge the suitability of the solvent to liquid chromatographic analysis and to give an overview about its analytical chromatography-oriented applicability. The new index has been used to evaluate traditional solvent-based liquid chromatographic methods as well as those based on alternative emerging green solvents and compare the factors together to give a universal overview that aids users to drive a rapid imprison on the weakness and strength aspects and makes it easier to judge the selection of the solvent and the evaluation of the overall method sustainability.