In-tube electro-membrane extraction with a sub-microliter organic solvent consumption as an efficient technique for synthetic food dyes determination in foodstuff samples

A simple and efficient extraction technique with a sub-microliter organic solvent consumption termed as in-tube electro-membrane extraction (IEME) is introduced. This method is based upon the electro-kinetic migration of ionized compounds by the application of an electrical potential difference. For this purpose, a thin polypropylene (PP) sheet placed inside a tube acts as a support for the membrane solvent, and 30 μL of an aqueous acceptor solution is separated by this solvent from 1.2 mL of an aqueous donor solution. This method yielded high extraction recoveries (63-81%), and the consumption of the organic solvent used was only 0.5 μL. By performing this method, the purification is high, and the utilization of the organic solvent, used as a mediator, is very simple and repeatable. The proposed method was evaluated by extraction of four synthetic food dyes (Amaranth, Ponceau 4R, Allura Red, and Carmoisine) as the model analytes. Optimization of variables affecting the method was carried out in order to achieve the best extraction efficiency. These variables were the type of membrane solvent, applied extraction voltage, extraction time, pH range, and concentration of salt added. Under the optimized conditions, IEME-HPLC-UV provided a good linearity in the range of 1.00-800 ng mL−1, low limits of detection (0.3-1 ng mL−1), and good extraction repeatabilities (RSDs below 5.2%, n = 5). It seems that this design is a proper one for the automation of the method. Also the consumption of the organic solvent in a sub-microliter scale, and its simplicity, high efficiency, and high purification can help one getting closer to the objectives of the green chemistry.