Carbonate esters as green alternatives in chromatographic separations.

Background: Carbonate esters are polar aprotic solvents that can be used to replace polar solvents: methanol, acetonitrile, or even apolar solvents in the mobile phases for liquid chromatography. Dimethyl, diethyl, and propylene carbonates (DMC, DEC, and PC) are not fully soluble in water.

Results: Twelve volume phase diagrams of water, the three carbonates, and methanol, ethanol, propanol, and acetonitrile were determined. They show that alcohols are much better carbonate/water mixing solvents than acetonitrile. DEC is the worst candidate as a green solvent. It needs too large amounts of mixing solvent to make a monophasic mobile phase useable in liquid chromatography. Also, it is the carbonate ester the most sensitive to water hydrolysis. The elution strength of carbonate esters is comparable to acetonitrile and stronger than methanol, but their viscosity is much higher. The more viscous carbonate ester containing mobile phases need higher working pressures, but the chromatograms did not necessarily show decreased peak efficiencies. Some selectivity changes are observed.

Significance: PC is highly preferable to DMC as a green organic modifier substitute. It seems to be the best green solvent substitute for methanol or acetonitrile if it is possible to work at a moderately higher temperature to compensate for the higher viscosity.