Development of a simple device for dispersive liquid-liquid microextraction with lighter than water organic solvents: Isolation and enrichment of glycyrrhizic acid from licorice

A simple device was developed that makes the use of lighter than water organic solvents feasible in dispersive liquid-liquid microextraction (DLLME) method. In the ordinary DLLME, the fact that a heavier than water organic solvent must be used, to be sedimented at the conical bottom of a centrifuge tube, limits the applications of this method in some extent. In the developed method, a glass tube with a narrow neck is inserted inside the centrifuge tube. After phase separation, the organic solvent is accumulated in the narrow neck of the device and therefore, can be simply collected by a micro-syringe. The DLLME method with the proposed device was tested for the enrichment of glycyrrhizic acid from aqueous extracts of licorice before analysis by a HPLC method. n-Hexanol and acetone were used as the organic and disperser phases, respectively. Effects of pH, salt concentration and phase volumes on the extraction of the analyte were optimized using a central composite (response surface) design. Under the optimized conditions (i.e. pH 1.3, ionic strength 0.2 mol L−1, n-hexanol 140 μL and acetone 0.8 mL) an extraction recovery of 104.1 (±5.1)% and an enrichment factor of 54 were obtained. The proposed method was successfully applied for the study of glycyrrhizic acid's level of licorice roots grown in three regions of Lorestan province, Iran, with different climate conditions.