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different half-cells. This is due to the effect of the interface within each half-cell. The relative values of this effect have been studied in mater and methyl alcohol. REFERESCES
OWEX:T h e Physical Chemistry of Electrolytic Solutions, pp. 314-16. Reinhold Publishing Corporation, S e w York (1943). (2) HARTLEY ASD MACFARLANE: Phil. Mag. 20, 611 (1935). . ~ S D HARTLEY: Phil. %lag.M), 734 (1925). (3) KONHEBEL
(1)
H . A R X E D ASD
T H E ELECTROCHEMISTRY OF PERMSELECTIVE PROTA,MINE COLLODIOK MEMBRANES. I RATE STVDIESo s
THE
ESTABLISHMENT OF THE CONCESTRATION POTENTIAL TYPESO F PERMSELECTIVE PROTAMINE COLLODIOK MEMBRAXES
ACROSS VARIOc.5
KARL FOLLSER’
ASD
HARRY
P.GREGOR2
Department of Physiology, Cniversity of Minnesota, Minneapolis 14, Minnesota, and the Laboratory of Physical Biology, Experiinental Biology and Medicine Institute, .Vutional Institufes of Health, Bethesda 14, Maryland Received A p r i l 1 1 , 1949
In two preceding papers (2, 3) improved and reproducible methods of preparation of various t’ypes of permselective (electronegative) collodion and (electropositive) protamine collodion membranes were described. I n addition to data on their water content these membranes were characterized by ( a ) the “characteristic concentration potential,” i.e., the potential of the chain 0.1 s potassium chloride membrane 0.01 K potassium chloride; ( b ) the “bi-ionic potential” (B.I.P.) of the chains 0.1 N potassium chloride 1 membrane 1 0.1 N lithium chloride and 0.1 N potassium chloride membrane 0.1 N potassium acetate, respectively; and ( c ) the electrical resistance of the membranes in contact with 0.1 s potassium chloride solution. In addition, certain data on the rate of ion exchange across a few of the membranes were presented. In subsequent publications a study was made of the rates at which final, stable concentration potentials wit,h various electrolytes are established across several types of permselective collodion membranes (8) and of the final concentration potentials established by various electrolytes a t different concentrations across these membranes (9). The present communication and the subsequent paper present analogous experimental studies with protamine collodion membranes.a
1
1
~
1 Present address: Laboratory of Physical Biolog,y, Experimental Biology and Medicine Institute, S a t i o n a l Institutes of Health, Bethesda 14, Maryland. Present address: Polytechnic Institute of Brooklyn, Brooklyn 2 , New York. 3 The authors wish t o express their thanks t o Eli Li11y a n d Company for the donation of the several samples of protamine sulfate which were used in these investigations.
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KARL SOLLNER AND HARRY P. GREGOR
I n considering the rate of the establishment of final, stable concentration potentials across these membranes, two fundamentally different possibilities must be distinguished. The first arises when a membrane saturated with critical ions of one species is brought into contact with the solution of an electrolyte having some other critical ion. Here, ion exchange-anion exchange in the case of electropositive membranes-must take place throughout the pore system of the membranes before final potentials can be obtained. I n the other case the membrane has already undergone ion exchange previously; with electropositive membranes the cationic (basic) wall groups are already compensated for by anions of the same species as the anions in solution. Here, an exchange of critical ions between the solutions and the membrane does not occur; only equilibration between the external solutions and the electrolyte in the wider parts of the pores of the membrane must take place. For reasons outlined previously (8) the former case involving ion exchange will be emphasized. The determination of the concentration potential ITas carried out with the conventional technique employing saturated calomel electrodes and saturated potassium chloride-agar bridge^.^ To minimize the contamination of the solutions by potassium chloride diffusing from the potassium chloride-agar bridges, the latter were dipped in the electrolyte solutions only for the duration of the actual measurements. The permselective protamine collodion membranes not being of ideal ionic selectivity, a significant leak of electrolyte across the membranes is likely to occur even a t low concentrations during the period in which the system reaches the final state. To avoid errors due to this factor or to contamination of the solutions with potassium chloride from the agar bridges, the two solutions separated by the membrane were renewed periodically. For the rate studies three types of membranes were selected from the large number of different varieties which were prepared. The system of designation of the membranes follows the previously established convention (3). A membrane designated as Hum 58-Shr 58 is one which mas dried on its mandrel a t 58 per cent relative humidity until equilibrium had been established, removed from the mandrel and dried once more without support of a mandrel (Le., “shrunk”) at a relative humidity of 58 per cent. The membranes (after being aged by a t least 3 days’ immersion in 0.1 N potassium chloride solution) were equilibrated for a t least 24 hr. with repeatedly changed distilled water, in order to remove ions of the critical species under investigation.&They were always returned to this state before use with a solution 4 The water permeability of these membranes is so low t h a t t h e stable potential is established before a detectable movement of water occurs (6). 6 For the case of the protamine collodion membrane i t has as yet not been established which species of ions is present in the membranes as counter ions of the fixed wall groups after prolonged washing with distilled water. I n the case of the (acidic) collodion membrane hydrogen ions were shown to be present (4, 5 , 7 ) ; with the protamine collodion membrane hydroxyl, bicarbonate (from the distilled water), and nitrate ions may be prese n t , the latter originating from the unavoidable, though very slow, hydrolysis of the cellulose nitrate (which is likely to be accelerated by the presence of the fairly strongly basic protamine).
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of different concentration of the same electrolyte or the solution of another electrolyte (8). In order that relatively small differences in the behavior of different electrolytes would not be overshadowed by minor differences between different membrane specimens of the same type, all experiments on the time effect reported for one type of membrane were performed with a single membrane specimen. Only electrolytes with univalent critical ions (anions) are discussed here. Preliminary experiments have shown that it is difficult to obtain meaningful data with electrolytes having bivalent anions; a separate investigation will be necessary for the adequate treatment of this problem. Figure 1 shows the rate of establishment of the concentration potential (at 25,OO"C. zt 0.05') for three different membranes with potassium chloride, potassium iodate, and magnesium sulfate for two concentration ratios, 0.01 x/O.OOl x and 0.1 x/O.Ol N. These data are given as measured, without correction for the asymmetry in the two liquid-junction potentials which arise between the potassium chloride-agar bridges and the two solutions of different concentration. The figures are accurate to about 0.10 mv. for the values in the final state.
I11 Figure 1 shows that the rate a t which stable potentials are established across the various permselective protamine membranes depends on the nat'ure of the electrolyte and the nature of the membrane, and also upon the absolute concentration of the solutions used. In some instances stable potentials are reached within less than 1 hr.; in other instances several hours may be required. d comparison with previously published rate studies on permselective collodion membranes6 (8) shows that the stable state with the permselective protamine collodion membranes is reached more slowly than in the former case.' The experimental data presented in figure 1 show specifically that the denser the membranes the more slowly are the final, steady potentials established. The difference between membrane Hum 2(tShr 20 and membrane Hum 58-Shr 58 at the higher concentration level is small, in agreement wit'h the close similarity of action of these membranes with respect to the final, stable concentration potential (3, 10). With potassium iodate, that is, with an electrolyte having a large anion, the stable state (with one doubtful exception) is reached much more slowly than with potassium chloride, which has an anion of smaller hydrated size. The rate at which the stable potential is established with potassium chloride and magnesium chloride is identical within the limits of significance of the experimental data. I n other words, the rate at which the final, stable concentration For the reasons outlined it does not seem promising t o make quantitative anion-exchange studies with protamine collodion membranes, analogous t o t h e cation-exchange experiments which have been carried out with collodion membranes (4, 5 , 7 ) . e The scale on the time a x k of figure 1 is one-half of the scale used in a n analogous figure in t h e paper on the rate effect with permselective collodion membranes (8). The probable cause of this difference between the permselective collodion and the permselective protamine collodion membranes will be discussed a t a later d a t e , when the ohmic resistance of these membranes will be considered.
'
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KARL SOLLXER .4ND HARRY P. GREGOR
potentials are reached seems to be practically independent of the nature (size and valency) of the noncritical ion. With more dilute solutions (0.01 s:O.OOl N ) equilibrium is reached somewhat faster than with more concentrated (0.1 x/O.Ol N) ones. 0.1N / 0 . 0 1 N
-58
OOlN/OOOl
N
-56 -54
-52 v)
I-
d -50 1 -I
-48
=! -58 5
z - -56 -54
t
5 -52
5
-50
2
0 -48 F: - 5 8 U a
-56 z w I-
p -54 0 0
-52
- 50 -48 -46
0 40 80 120 I60 200 240 280 320 0 40 BO 120 IbO 200 240 280 320360 TIME IN MINUTES FIG 1 The rate of establishment of steady concentration potentials c? c , = 10 1 of several electrolytes across various permselective protamine collodion membranes
These results are strictly parallel with those obtahed for the permselective collodion membranes. The observation is confirmed that the nature and valency of the noncritical ion do not play an important role with regard to the rate a t which the final, stable concentration potentials are established. The possible significance of these results for the broader problem of the geometrical and electrical structures of membranes of porous character was indicated previously (8). With respect to the rate of establishment of the concentration potential across membranes which are already saturated with the critical ion species by prior ion
PERMSELECTIVE PROTAMISE COLLODIOS MEMBRANES. I
329
exchange, it might be reported that these rat'es are much higher and less characteristic for the different ions, in agreement with the results obtained with the electronegative collodion membranes. From the practical point' of view, however, it is interesting t,o note that with such membranes final, stable potential readings can frequent,ly be made almost instantaneously, in most instances within 2 min.; adaptation periods of more than 10 min. are rare. SUMXkRY
1. A study was made of the rates a t which final, stable concentrat,ion potentials are established with three electrolytes-potassium chloride, potassium iodate, and magnesium chloride-across three types of permselective protamine collodion membranes which had been carefully freed of ions of the critical species, that is, the anions of the elect,rolytes in the external solutions. 2 . The rates at which stable concentration potentials across these membranes are established depend on the nature of the membrane, the nature of the electrolyte, and the absolute concentrations of the adjacent solutions. The time required for the establishment of final stable potentials varies from less than 1 hr. up t o several hours. Specifically, it was found that: (a) the denser the membranes the more slowly are the final steady concentration potentials established; ( b ) with potassium iodat'e, i.e., with an electrolyte having a large critical ion, equilibrium is reached much more slowly than with potassium chloride, an electrolyte having a critical ion of smaller hydrated size; (c) the rates a t which equilibrium is established with potassium chloride and magnesium chloride are identical within the limits of the significance of the experimental dat,a; in other words, the rate a t which the final, stable concentration potentials are reached seems t o be practically independent of the nature (size and valency) of t,he noncritical ion (the cation); ( d ) n i t h more dilute solutions (0.01 s / O . O O l x) equilibrium is reached somewhat faster than with more concent,rated (0.1 s;O.O1 s) ones. 3. The establishment of stable concentration potentials across membranes which are already saturated nith the critical ion species by prior ion exchange occurs much faster than in the cases where ion exchange must occur; stable potentials are frequently obtained nearly instantaneously, adaptation periods of more than 10 min. being rare in this case. 4. The experimental results obtained with the (electropositive) permselective protamine collodion membranes and the conclusions which can be derived from these data are strictly parallel to t,hose obtained previously nith (electronegative) permselective collodion membranes. REFEREKCES (1) GREGOR,H.P . : Ph.D. Thesis. Cniversity of Minnesota, 1945. (2) GREGOR,H . P., I S D SOLLSER,K . : J. Phys. Chem. 60, 53 (194G). (3) GREGOR,H . P . , A S D SOLLNER, K . : J. Phys. Chem. 60, 88 (1946). (4) SOLLSER,K . : J. Phys. (:hem. 49, 4 i , 171 (1945). ( 5 ) SOLLSER,K . , ASD ASDERMAS,J . : J . Gen. Physiol. 27, 433 (1944). (6) SOLLSER,K . , A K D CARR,C H . K . : J . Gen. Physiol. 28, 119 (1944). ( i )SOLLSER,K . , CARR,C H . W., ASD ABRAMS,I . : J. Gen. Physiol. 26, 411 (1944)
330
KARL SOLLNER AND HARRY P . GREGOR
(8) SOLLNER, K., AND GREGOR, H. P . : J. Phys. Chem. 60, 4iO (1946). (9) SOLLNER, K., A N D GREGOR, H. P . : J. Phys. & Colloid Chem. 61, 299 (1947). K . , A N D GREQOR, H. P.: J. Phys. & Colloid Chem. 64, 330 (19.50). (10) SOLLNER,
T H E ELECTROCHEMISTRY OF PERMSELECTIVE PROTAMISE COLLODION MEMBRASES. I1 EXPERIMEXTAL STUDIES ON THE CONCENTRATION POTENTI.4L ACROSS VARIOUS TYPESOF PERMSELECTIVE PROTAMINE COLLODIOX MEMBRAXES TTITH SOLUTIOKS OF SEVERAL ELECTROLYTES KARL SOLLNER’
AND
HARRY P. GREGOR2
Department of Physiology, University of Minnesota, ikfinneapolis 14, Minnesota, and the Laboratory of Physical Biology, Ezperimental Biology and Medicine Institute, National Institutes of Health, Bethesda 14,Maryland Received April 11,
lQ4Q
I The preceding paper (19) presents data concerning the rates at which final, stable concentration potentials with various electrolytes are established across several types of permselective protamine collodion membranes. The present paper is a further contribution to the systematic investigation of the permselective membranes and presents an experimental study of the final, stable concentration potentials established by various electrolytes a t different concentrations across several types of permselective protamine collodion membranes. Not only are such studies necessary to enhance an understanding of the fundamental physical chemistry of membranes of porous character, but they are also desirable in view of the usefulness of these membranes in such investigations as, e.g., the study of Gibbs-Donnan membrane equilibria (5, 13, 14, 16) and in the electrometric determination of ion activities (3, 5, 12). The present investigation is parallel in plan, theoretical background, and technique t o an earlier study on the concentration potentials arising across (electronegative) permselective collodion membranes (18). Certain details which are treated briefly here are describkd in greater length in this previous paper. I1 The physical meaning of experimental concentration potentials measured across ion-selective membranes can be visualized best by reference to the t,heoretical limits of the possible electromotive properties of real membranes. With membranes of high ionic selectivity the more important of these limits are the 1 Present address: Laboratory of Physical Biology, Experimental Biology and Medicine Institute, Kational Institutes of Health, Bethesda 14, Maryland. 2 Present address: Polytechnic Institute of Brooklyn, Brooklyn 2, New York.
