Journal of Membrane Science, 57 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIH (1991) 321-336 Elsevier Science Publishers B.V., Amsterdam 321 Electrodialytic production of gas-free sodium hydroxide based on Donnan breakdown Douglas L. Strong and Purnendu K. Dasgupta Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409-1061 (USA) (Received August 2,199O; accepted in revised form December 5,199O) zyxwvutsrqponmlkjihgfed Abstract An approach to generating high purity NaOH solutions in a continuous flow system by electro- dialytic means is described. Sodium hydroxide of ordinary purity flows along one side of a per- fluorinated cation exchange membrane; this channel also contains a noble metal anode. Sodium ions from this donor channel are elctrodialyzed across the membrane into a flowing water receptor channel, bounded on the other side by an identical membrane. This membrane is in intimate contact on its far side by a perforated inert plate, beyond which the cathode is located. Water flows through the cathode channel. The restrictor plate causes the accumulation of high concentrations of NaOH on the electrode side of the cathode membrane, resulting in its eventual Donnan break- down and passage of cathodically generated OH- through it to the central channel. From the purity of the H+ -exchanged conductance of the NaOH solution generated, it is estimated that the generated product is at least an order of magnitude purer in terms of carbonate contamination relative to the feed NaOH solution. The pure NaOH generated is directly fed into a high pressure pump and used for anion chromatography. Keywords: ion-exchange membrane; electrodialysis; Donnan breakdown; ultrapure chemicals Introduction In suppressed anion chromatography, presently widely used in anion anal- ysis, an alkaline eluent, e.g. Na,CO,, flows through an ion exchange column and then through a cation exchange membrane (CEM) device called a sup- pressor which exchanges all influent cations for H+ and finally into a conduc- tivity detector [ 1,2]. The suppressor converts the eluent to weakly conducting H&O, while sample ions, e.g. Cl-, NO;, SOi- etc. are converted to the strongly conducting acids, HCl, HNO,, H,SO, etc. and are sensitively detected down to fig/l levels. The CEM-based suppressor is continually replenished by continuously flowing dilute acid solution on one side of the CEM while the column effluent flows on the other [ 31 or the Na+ in the column effluent may be taken out electrodialytically into a water receptor [ 41. 0376-7388/91/$03.50 0 1991- Elsevier Science Publishers B.V.