Finding the ideal solvent for the analysis of polar analytes using supercritical fluid chromatography

The analysis of polar analytes with the help of hydrophilic interaction liquid chromatography (HILIC) using classic methods of high-performance liquid chromatography is not without its downsides. In these applications, acetonitrile is prevalent as main eluent and sample diluent. This results not only in slow diffusion processes during the separation, but also in often unstable sample solutions where polar analytes are concerned. Furthermore, there are ecological concerns. With the use of supercritical fluid chromatography (SFC) which uses supercritical carbon dioxide as eluent, and other green solvents as alternative for the sample preparation, the separation of polar analytes could be vastly improved with this technique. Fast diffusion within carbon dioxide led to shorter analysis times and higher plate numbers. Regarding sample diluents, small alcohols such as ethanol and 2-propanol, as well as acetone, yielded promising results while analytes showed higher solubility and stability within these solvents compared to acetonitrile. Other green solvents such as dihydrolevoglucosenone (Cyrene) and dimethyl carbonate were found to be unsuitable sample diluents for applications in SFC.