ELECTRODIALYSIS WITH SIMPLE APPARATUS"
A brief historical account of the invention of electrodialysis i s given. It i s pointed out that even though a considerable number of scientists haere applied the method, i n research as well as in indwtry, and while reviews of the subject have been published, the process i s still one of the you$ of the "neglected methods." The adwantages, however, are in many instances so uneqnivocul that it should have a very definite place among the methods of organic chemistry. The principles involved i n the pocess of electrodialysis make its study both interesting and instructive (a number of cases have been reported which offered results unobtainable by any other method). The fact that electrodialysis remains among the "neglected methods" may be accounted for as follows: (1)it i s ordinarily given inadequate treatment i n textbooks; (2) its advantages and applicability are not generally recognized; (3) simple and eficient types of electrodialyzers for general laboratory use are scarce. Two machines which worked satisfactorily in the writer's laboratory are described and photographs are included. One machine i s wed for experiments on a small scale, and the other for larger volumes. I n both cases, the apparatus can be easily set u p from glassware that i s readily obtainable. That process to which the term "electrodialysis" is applied, is a comparatively recent invention, frequently credited to W. Pauly. In a recent review on this subject (1927), Charles Dhere claimed priority as an independent discoverer, basing his claim on papers published around 1909 ( I ) . He admitted, however, that two American scientists (2) had already used the fundamental principle in 1903, but had failed to emphasize the general applicability and value of the method. A few months later, J. Reitstoetter (3) amplified the bibliographical data of the French author, making special reference to work which had been done in the industrial field which had not been mentioned in the Dhere report. Thus it appears that as early as 1896, D. Wmkler, in the British Patent Number 5749, described a method for the purification of albumoses and protein degradation products by means of the electric current. Credit has also been given to Count Botho Schwerin, the lawyer-inventor of Germany, for extensive work in connection with the developments of the electrodialytic process. His first patent [D.R.P. 168,8531, granted in 1900, was for a method of purification of substances of cellular origin and proteins by means of the electric current. In it is found a precise explanation of the process and the principles in-
* Delivered before the Division of Chemical Education at the 81st meeting of the A. C. S. at Indianapolis, Indiana, April 1, 1931. 1634
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volved, which are very properly described as a combination of two simultaneous parallel processes, namely the electrolysis of the dissociating substances and of the electroendosmosis of the substances which are not dissociated. It may be interesting to recall here another definition of the electrodialytic process given by H. Freundlich and L. F. Loeb (4) in 1924, according to which electrodialysis is a combination of dialysis and electrolysis: the separation of electrolytes from a colloidal system through semipermeable membranes. Even though a review of the literature shows quite clearly that a considerable number of scientists have applied electrodialysisboth in researches and in industry, the process is still one of the group of the "neglected methods" if compared with the wide field of possible application. The advantages, however, are in many instances so unequivocal that it should have a very definite place among the methods of science, also the principles involved make the study of the electrodialytic process both interesting and instructive. There appear to be several reasons for electrodialysis being a "neglected method," a few instances may be cited. 1. In the first place, a survey of a number of textbooks on various branches of chemistry shows that only a few (5) give the subject adequate attention. 2. The advantages and applicability of the method have not been generally recognized. 3. Even though quite a few machines for special electrodialytic purposes are described by various authors, there seems to be no simple and efficient type of electrodialyzer for general laboratory use. The first objection cited above can be overcome only by a complete description of the method in textbooks of wide circulation. The second point might be somewhat neutralized by enumerating and re-emphasizing the broad variety of possible applications, while the lack of a suitable electrodialytic outfit might be overcome by describing two simple types of apparatus which have been used to best advantage in our laboratory. Without attempting a complete enumeration of the fields in which electrodialysis has been successfully used, since this has been so well done in the two reviews which have already been referred to, the following should be mentioned. I . In the chemistry of high polymers, comprising proteins, cellu2ose and its esters, starch and similar substances. This type of compound is especially suitable for electrodialytic purification on account of the high molecular weight of the substances which comprise it. In virtue of this weight, they encounter difficulties in parsing through semi-permeable membranes, while their impurities, such as inorganic electrolytes, organic crystalloids, and substances of small molecular weight, migrate through the diaphragm, especially when under the influence of an electric potential. I t is, therefore, quite natural that the
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early work centered around this type of substance. The results obtained were very satisfactory and as a rule superior to other methods of purification. The last traces of inorganic impurities of gelatin and nitrocellulose can also be eliminated only by electrodialysis. 11. Degradation products and carbohydrates of smaller molecular weight. The separation of protein hydrolysates into a primarily basic, a chiefly acid, and a third fraction which has neither a pronounced acid nor alkaline character, has been achieved by electrodialysis in a three-chamber apparatus. The importance of maintaining a definite pH in order to obtain certain effects was also brought out in the study of these substances. By this method, for example, histidine can be separated from arpiniue and lysine (6). The isolation of glycocholic add (7) from bile extract will serve as another example. The separation of physiologicauy active bases from proteins or degradation products was recently accomplished when protein or gelatin solutions c o n t a i i g histamine or choline were successfully electrodialyzed and the base recovered (8). 111. The successful purification of alkaloids by this method might conceivably lead to preparations of standardized purity for pharmaceutical purposes (9). IV. Interesting results were obluined m'th enzymes: amylase, which after prolonged dialysis is still active toward starch, was found to have lost its activity when electrodialyzed (10). When electrolytes are again added, however, its power of fermentation is said to be restored. If these experiments should prove to be duplicable, a very interesting aspect of enzyme action would have been brought out by means of electrodialysis. V . In thefield of antibodies and hormones, interesting findings have been made which may prove to be of general importance. Certain antitoxins, as that of diphtheria serum, can be concentrated and separated by electrodialysis under proper conditions (11). In this connection, the isolation of immunizing substances in general should be mentioned as of major importance (12). Successful work has also been done in the field of insulin separation (13). In the following paragraphs two machines will be described which work rapidly and efficiently. They have been designed with the purpose of obtaining an appliance which can be rapidly and easily set up in every laboratory, and which should enable more extensive work to be done in this field. For small samples and preliminary experiments, the three-compartment vessel as shown in Figure 1was used. It is made of a short piece of glass tubing of any desired width [the one illustrated being 3" X I"]. This tube is provided with a fair-sized hole blown into the middle of the wall. Two other glass tubes of desired length, and either slightly larger or smaller than the one just described, are also provided with a hole and are used as
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the two outer compartments. In place of membranes, parchment paper is folded over one opening of each of the tubings. If the middle tube is of slightly wider diameter, they are inserted.* If smaller, the end tubes are slipped over the middle piece after the parchment is in place. A rubber band and collodion are used in adjusting the apparatus and making i t
* A piece of rubber tubing can also be used as a middle cell. paratus can be made in U shape to facilitate cooling.
If desired the ap-
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tight. This is clearly shown in the photograph. The electrodes, preferably platinum wire, are inserted each through a two-hole stopper which also holds glass tubings through which the contents of the outer cells may be siphoned away. This apparatus may be varied in size for any desired purpose. Direct current and possibly a lamp resistance will he all the additional equipment necessary for experiments on a small scale. The second apparatus, which is shown in Figure 2, A and B, is designed for the electrodialysis of larger volumes. Selectionsfrom the stock of glassware of a laboratory supply house* were drawn upon for the apparatus as finally made. The two outer cells were made of bell jars in the walls of which two holes were bored opposite each other. For the middle cell, a glass jar with a ground glass cover of the same diameter as the base of the bell jar was chosen. The bottom of this jar was cut out to provide a glass cylinder with two open sides.** A sufficient amount of the bottom was left to be used as a flange. BeI tween the three compartments, parchment m e m b r a n e s were placrd. T h e y were held togethrr hy a simple cradlc-like FIGURE 2B wooden stand. A sliding head block which may be forced against the glass apparatus by means of four bolts holds the parts firmly in position. The electrodes were inserted through the tubulatures of the bell jars. A thin platinum disk may be used for the anode chamber; inexpensive nickel electrodes proved satisfactory as cathodes. Literature Cited Kolloid-Z., 41, 243, 315 (1927). ( I ) DHERE, Z. physik. Chen.,45, 606 (1903). (2 ) MORSEAND PIERCE,
* The glass parts can now be supplied by E. Sargent & Co., Chicago, Ill. ** A rubber ring between the cells proved advantageous.
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(3) REIT~TOETTER. Kolloid-Z.. 43, 35 (1927). (4) FKEUNDLICH AND LOEB, Biochem. Z., 150, 522 (1924). (5) GORTNER, "Outline of Biochemistry," John W'iey & Sons, Inc.. New York City, 1929, pp. 73-5. (6) ImDA AND SUZUKI, U. S. Patent 1,015,891; FOSTERAND SCHMIDT, P ~ c SOC. . Ezp. Biol. Med., 19, 348 (1921-22); J. B i d . Chem., 56, 545 (1923); Nocucm, Bull. Ins!.. Phys. Chem. Research, 8, 152 (1929). (7) KEILAND SCHIECK,Z. Bid., 88,153 (1928). AND KENDALL, in print. (8) GEBAUER-FUELNEGG B. Pharnz., 25, 379 (1915). (9) TRAWBE, AND VULQUIN, Compt. rend. soc. Biol., 72, 336 (1912). (10) LISBONNE (11) ADOLF, Klin. Wochschr.,3, 1214 (1924). (12) LOCKEAND Hmsca, J. Infectious Diseases, 35, 519 (1924). (13) Locm AND Hmscn, J. Am. Med. Assoc., 83, 1913 (1924); TAYLOR, BnAuN, SCOTT,Am. J. Physiol., 74, 539 (1925).
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