On the use of ethylene carbonate as a green solvent in mobile phases

Dimethyl, diethyl, and propylene carbonate esters are polar aprotic solvents that demonstrated their capability as "green" solvents compared to methanol, acetonitrile or even apolar solvents in mobile phases for liquid chromatography. Ethylene carbonate (EC) has a melting point of 36 °C, so as a solid, it cannot be used as a neat solvent in liquid chromatography. However, its molten state is fully miscible with water and such solutions can be effective liquid chromatographic mobile phases. In this work, EC was used for the first time in a variety of liquid mobile phases since its freezing temperature can be lowered at or below room temperature by mixing it with other solvents. The freezing temperature of EC mixed with different proportions of a variety of common solvents as well as with other carbonate esters is presented. The viscosity changes induced by these mixtures were estimated using the experimental driving pressures (Darcy's law). A hydrophilic interaction liquid chromatography (HILIC) separation of nucleosides could be improved by replacing a large part of acetonitrile by EC. RPLC separations of phenols and less polar aromatic hydrocarbons could be performed by entirely replacing acetonitrile by EC. UV detection at 220 nm was possible, but background removal was required when a solvent gradient was used. The EC elution strength is slightly lower than that of acetonitrile. EC is definitively a very green solvent that must be considered with both HILIC and RPLC modes. However, it is not without some drawbacks in all applications since its 243 °C boiling point precludes the use of evaporative light scattering detectors and makes electrospray ionization difficult. EC is not soluble with alkanes. The EC/heptane/ethanol phase diagram showed that >72 % ethanol is needed to obtain EC monophasic mixtures. Therefore, EC will have little use in normal phase chromatography.