Electrochimica Acta, Vol.296, 355-363, 2019
Impedometric investigation of salt effects on electromembrane extraction: Practical hints for pH adjustment
In the current work, an impedance system is developed to investigate the time variation of solution resistance, membrane resistance, and double layer capacitance during electromembrane extraction from salty solutions. For this purpose, the adverse effects of various salts such as NaCl, NaF, NaNO3, KNO3, KCl, LiCl, CH3COONa, Na2SO4, Na3PO4, MgCl2, LiCIO4 and K2CO3 are studied. Two different model analytes are used including Naproxen and Verapamil as an acidic and basic drugs, respectively. In order to obtain a quantitative measure of the adverse effect of various salts, the recoveries were calculated along with those for the extraction from salt free donor phases. The decline of the recovery (called suppression throughout this work), due to the presence of the salt was taken as the quantitative measure of the adverse effect. In the case of the acidic drug, the percent suppression values had a wide range from 26.95 to 85.23%, except in the presence of LiClO4 which gave a suppression of 100%. The presence of salts during the extraction of the basic model analyte resulted in two different patterns. While NaNO3 and CH3COONa caused complete (100%) suppression, the rest of salts gave lower suppression values in the range of 16.99-38.32%. The impedance analysis results show that the free energy of transfer of accompanying ions has a significant effect on the time dependence of solution resistance and double layer capacitance. It is also shown that the suppression of recovery is significantly correlated with the rate and timescale of depletion of ionic species from the donor solution as well as the propagation of the double layer. In summary, it can be concluded that, when working with simple acids/bases for pH adjustment in EME, smaller counter ions are preferred. (C) 2018 Published by Elsevier Ltd.