Electrolytic Desalting with Ion-Exchange Membranes

Abstract

SEPARATION of amino-acids and other substances by paper chromatography must often be preceded by the removal of inorganic salts. The common methods¹ require careful supervision, and under optimal conditions a loss of 10–20 per cent of many amino-acids may occur with 50 per cent loss of arginine by conversion to ornithine². A simplified form of desalter, employing ion-exchange membranes, as suggested by Astrup and Stage³, has been used in this Department for the routine preparation of plasma, urine and cerebrospinal fluid for paper chromatography. The apparatus consists of a small ‘Perspex’ container separated into three compartments by ion-exchange membranes (Fig. 1). The solution to be desalted in the centre compartment (3 ml.) is separated from the anode by an anion exchange membrane (‘Permaplex’ A.10) and from the cathode by a cation membrane (‘Permaplex’ C.10, both obtainable from Permutit, Ltd., London, W.4). The anode and cathode chambers are filled with 0.2 N sodium hydroxide and sulphuric acid respectively.