Separation of fluorescent derivatives of hydroxyl-containing small molecules on a microfluidic chip Original Research Article

Capillary electrophoresis (CE) on a microchip has been employed in this work because of the need to separate and detect fluorescent derivatives on some licorice-derived compounds, namely glycyrrhizin (GL), isoliquiritigenin (IQ). These compounds, which contain only phenolic or aliphatic hydroxyl (secondary) groups, are hard to derivatize in aqueous solutions. Although there are some fluorescent reagents that will react with hydroxyl groups, these reactions are usually achieved in aprotic solvents, but not in aqueous solutions. The only fluorescent reagent that works in aqueous solvents is 5-([4,6-dichlorotriazin-2-yl]amino)fluorescein (DTAF), but it has mostly been employed to label macromolecules. For the first time, we have successfully fluorescently label two hydroxyl-containing small molecules, GL and IQ in aqueous solutions. The reaction products were separated by CE and detected fluorescently on a microfluidic chip within 100 s. For comparison, the separation was also carried out on a commercial CE system using UV absorbance detection.