Electrodialysis of organic acids, organic bases, and alkaloids across ion exchange membranes. III. On the permeability of caffeine and ephedrine

Abstract

Permeability of caffeine and ephedrine through the cation-exchange membrane was examined by the use of five-compartment cell and heterogeneous ion-exchange membrane prepared in the laboratory. Each compartment of the cell contained stock solution of various compositions, concentration chamber was fixed, and the dilution chamber in the center was flown with the stock solution, from the bottom to the top. Electrodialysis was carried out for 1 hour and the amount of each ion in the sample solution in the concentration chamber was determined by the conventional method. Some noteworthy results of this experiment are given below.1) Ephedrine and caffeine can be concentrated to over 3 times and 1.7 times, respectively, of the original concentration, ephedrine by the use of a weak acid resin membrane, at a strong acidity and high current density, and caffeine by the use of a strong acid resin membrane, at pH 3, and a high current density.2) Permselectivity coefficients of ephedrine and caffeine, when using sodium ion as the reference standard, both become over 20 times and 5 times, respectively, higher by the use of a weak acid resin membrane, in a region below pH 1, and a low current density.3) The use of a high current density at a neutral solution results in markedly small parmselectivity coefficient and this makes it possible to remove contaminating inorganic ions.4) The ease of permeability is greater in caffeine than in ephedrine through a strong acid resin membrane but this order is reversed with a weak acid resin membrane.