Chromatographic Properties of Ethanol/Water Mobile Phases on Silica Based Monolithic C18

For almost 10 years, silica-based monolithic stationary phases have been used in numerous fields of analytical chemistry, especially when high flow rate is required or for the separation of high molecular weight compounds such as peptides. In comparison with particulate stationary phases, the macroporous structure of the silica rod induces low pressure drops, which allows the use of high flow rates, leading to a dramatic reduction of the analysis duration. We suggest another use of this type of phases with mobile phases having a high viscosity, such as ethanol–water mixtures. These mobile phases are environmentally friendly, avoiding the use of toxic solvents such as methanol and acetonitrile, and consequently the necessary cleaning of waste is reduced. In this paper, the eluting strength of different hydro-organic mobile phases and their efficiencies are compared on Chromolith RP-18e. Due to higher eluting strength, the use of ethanol–water mixtures also allows decreasing the amount of organic solvent required to achieve a separation, whereas, despite a higher viscosity, the chromatographic efficiencies are as good as those obtained with classical mobile phases. Finally, separation of pesticides (triazines) and sunscreen molecules are presented.