Electrophoretic micro-preconcentration of ionizable compounds as a green approach in sample preparation

A green, simple, and efficient micro-preconcentration method termed electro-micro-preconcentration is introduced. This organic solvent-free method is based upon the electro-kinetic migration of the ionized compounds under study by the application of an electrical potential difference. In a glass tube, used as a preconcentration unit, 1 mL of the aqueous sample solution under investigation was added, and two electrodes (as the anode and cathode) were placed at the two ends of the tube. By choosing a proper tube diameter and length (4 mm and 10 cm, respectively), the convection and mass diffusion were reduced. Under these semi-stagnant conditions, the synthetic food dyes under investigation (as the anionic analytes) migrated from the cathode to the anode by applying a low electrical potential difference, and they were concentrated around the anode (the preconcentration area, 100 μL). The effects of some important parameters including the preconcentration time, applied voltage, pH range, and ionic strength on the preconcentration efficiency were investigated and optimized. Under the optimal conditions, the proposed method provided a good linearity in the range of 0.005-15 μg mL− 1, suitable limits of detection (0.001-0.015 μg mL− 1), good preconcentration recovery (29-40%), and good repeatability (RSD values below 9.8%, n = 5). The method was successfully applied to the preconcentration of some synthetic food dyes as the model compounds in a number of food-stuff samples.