was successfully demonstrated early in 1960. Discussions with makers of gas chromat,ographs later led to the recent introduction of two additional commercial double-column programmed temperature gas chromatographs.
of Lewis Fowler, A. J. Bindbeutel, and J. W. Sharp in constructing certain components for the instrument is also
Harden, J. C., Ibid., r
gratefully acknowledged. We thank G. Forrest Woods of the Universitv of Maryland for his generous donati& of the quaterphenyl isomers.
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ACKNOWLEDGMENT LITERATURE CITED I,,
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RECEIVED for review November 21, 1960. Accepted February 13, 1961. Division ?fn&nn;iytioal,Chemistry, . r ~ 139th Meeting, T~
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tiectrocnromatogrciphic Separation of Silver and Thallium Ions from Each Other and from Mixtures of Vu rious PoI yva lerl t Cations HAROLD H. STRAIN, JOHN F. BINDER,' G. HARLOWE EVANS,%HARLAN D. FRAME, Jr., and JOHN
J. HlNES
Argonne National laboratory, Argonne, 111.
b Differential electricol migrotion in on ommoniacal solution of oxalate plus cyanide provides a complete separation of thollium ions from silver ions and from various polyvalent cotions. Migration in an ommoniacal solution of ammonia-triacetic acid provides a complete separation of silver ions from thallium ions and from various poly-
The addition of buffered citrate to the background solution, for example, converted the divalent cations to anionic complexes leaving the alkali metal ions as uncomplexed cations. This observation indicated that all polyvalent ions might he removed from mixtures as
moniocol oxalote solution provides o separation of silver plus thallium ions from various polyvalent cotions. These migrations in the presence of complexforming solutes a r e rapid and complete even ot minute concentrations of the ions.
T,
HE n I F F E R m T m L electrical migration of ions from a narrow zone in a stabilized background electrolytic solution provides a sensitive and effective method for the separation of mixtures of various substances (5-6, 9-1s). These electrochromatographic separations depend upon the solvent ( I S ) , the background electrolyte (3,7), the stabilization medium (81, and the electroosmotic flow of the solution (1). They are effective over wide ranges of concentration, from about 0.10M to the lowest concentrations that can be detected by the most sensitive tests (6). Evans and Strain have shown that the separation of the alkali metal cations from the alkaline earth cationsis improved by the addition of complexing
Present address, Laminated Products Demrtment. General Electric Go.. Coshocot,. Ohio. ' Present address, Department of Chemistry, Illinois State Normal University, Normal, Ill.
anions ieavlng ail monovalein elemems as cations. T o exploit thc possibility of separating monovalent mercurous, silver, and thallium ions from polyvalent cations, we examined the effect of many complexing agents, mixtures of these snhstances, and variation of the pH on the differential electrical migration of various cations. Procedures have been found that permit the separation either of silver or thallium from multicomponent mixtures of various ions, and also the separation of silver and thallium from one another and from any one of several of the polyvalent ions. As indicated by the most sensitive tests, these separations, based upon electrical migration in opposite directions, are complete wit.hout any cross contamination. EXPERIMENTAL
Stabilization Medium. The background solutions were stabilized with commercial filter paper made of wood pulp (Eaton-Dikeman Co., Grade 301; thickness 0.030 inch). Several sheets were washed by downward percolation with 6 N nitric acid for 1 day and then v i t b distilled water for 4 days using the arrangement shown in Figure 1. The mashed , . > sheets . . were separated an$ . 1~
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VOL. 33, NO. 4, APRIL 1961
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527
ends of the paper were placed in electrode vessels cut from solidified polystyrene foam. The paper was soaked with the buffer to be tested, and the excess was drained into the electrode vessels a t each end. Then about 10 fil. of a 0.05M solution of each ion to be tested were added to the particular marked spots. The moist paper was covered with a sheet of polyethylene; electrolytic solution in the two vessels was levelled with a siphon after large graphite electrodes were placed in the vessels; direct current electrical potential was applied; and the migration was carried out for 1 to 4 hours. The electrical current was turned off, and the zones of migrating ions were located with suitable reagents which revealed a series of spots as indicated in Figure 3. The water-cooled supports for the paper were made in two ways: as hollow vessels (Figure 2) and as cooled metal plates. Although made of stainless steel and reinforced by spot welds to steel strips on the inside, the hollow vessels were easily swelled hy a sudden increase in the water pressure. Accumulation of air from the water reduced the cooling efficiency. Both these effects were alleviated by use of a b y p a s that provided a water head of only 2 to 3 feet. A more robust cooling plate was obtained by soldering copper tubing to one side of a copper plate inch thick. For migrations at a relatively high potential (16 volts per em.) for short periods, a sheet of washed paper ahout 8 inches wide and 2 feet long was placed on a sheet of polyethylene across a thick piece of aluminum (3/* by 12 by 24 inches). With this arrangement, the starting line for the zones of the ions was near the anode so that the cations had an available migration distance of about 10 inches. At potentials of about 16 volts per cm. and with
Figure 2. Arrangement for electrochromatography with filter paper supported on insulated water-cooled vessel Ends dipping into electrode vessels provided with large grophite electrodes
reduced concentration of the background solution to prevent heating, extensive separations were obtained in 0.5 to 1 hour. Background Solutions. The background solutions were selected with several objectives in mind: namely, effective separation of the ions, suitable electrical conductivity and pH, absence of chemical elements t h a t would be activated by neutrons, and noninterference with detection tests. The background solutions that were most effective for the isolation of silver or of thallium ions were those in which only the desired ion remained as a cation. I n some of these solutions, two or three complexing agents were required to facilitate the selective migrations. Some of the background electrolytes and certain complexing agents were strong electrolytes. To restrict the conductivity of the solutions and to reduce the heating effects, even a t low
Figure 3. Reproduction of electrochromotogrom showing relative migrotion of various ions 10 wl. of 0.05M solutions added to paper moistened with 0.35M iadic osid in 0.25M ammonia; pH, 4.4; potentiol. 4.4 volts per cm., current, 280 ma.; time, 4 hours; detection reagents, os indicated. Color of zones; b, black; br, brown; 0, orange; y, yellow; g, green; p , pink; fl, fluorercent; Alk, olkoline; Am, ammoniacal
528
ANALYTlCAL CHEMISTRY
electrical potentials, it was necessary to limit the concentration, Other electrolytes, such as the ammonia employed as a pH buffer, were so weakly dissociated that they could be employed a t very high concentration. Ammoniacal solutions not only provided suitable pH huffering capacity and electrical conductivity, hut they also permitted appropriate complex formation. I n the ammonia solutions, the migrating ions formed well defined zones. After the migration, the ammonia was easily removed by evaporation, thus facilitating certain detection tests. I n the ammoniacal solutions, mercurous ions underwent dismntation yielding mercury and mercuric ions. In most acid solutions, all the common cations migrated to the cathode. I n these solutions, thallium ions migrated faster than silver ions, which, in turn, migrated faster than most of the polyvalent cations. Under these conditions, the migrating silver ions often yielded a long trailing zone so that the separations were incomplete. This trailing effect was not observed in the ammoniacal solutions. I n certain acid solutions as with citric, lactic, and hydrochloric acids, some of the ionic silver was precipitated at the point of addition. Migrating from these precipitates in citric and lactic acid, the silver ions formed long diffuse zones. The conducti~ty of the migration systems was adjusted to suit the applied voltage by variation of the concentration of the electrolyte. The lower the concentration, the lower the conductance, the lower the current, and the smaller the heating effect. Because the conductance and the current were proportional to the width of the paper, and
Figure 4. Seporotion of silver plus thallium ions by electrochromotogrophy Paper moistened with O.OSM ammonium oxalate in 0.2M ammonie; pH, 9.8; potentiol, 16 volts per Em.; current, 350 m a , time, 1.08 h o w . Mixture of 15 cotiom added os 5 odiosent zones of 2pl. each (15 described in section on initial zones
because the current output of the electronic rectifiers was limited to about 500 ma., narrower sheets of paper were employed a t high potential than a t low potential. Initial Zones. For comparison of the mobility of cations in various background electrolytic solutions, a small portion (10 pl.) of the solution of each ion was placed on the moist paper. These samples were small and the concentration was low (0.05M) so that the added species would react rapidly and completely with the complex-forming reagent. A high concentration of the added ions relative to the concentration of the background solution always leads to the formation of diffuse zones (6). The size of the initial zone must be adjusted to the increase in size during migration and, therefore, to the distance of migration. The size of the zone and the concentration in the zone must also be adapted to the concentration of the complexing agent in the background solution (8). There is, therefore, an upper limit with respect to the volume and concentration of the solution added as an initial zone. Under favorable conditions, all the added ions remain in their respective migrating zones. For location of the zones, however, enough material must be added initially so that it is detectable after the migration and the concomitant dilution. Most of the solutions were submitted to migration from single spots a t a concentration of 0.05ilf. These solutions were prepared by dilution of 1.OM stock solutions of chlorides, nitrates, or acetates. Antimony chloride and arsenic chloride solutions (1. O M ) were stabilized with 31 and 25 ml. of concentrated HC1 in each 100 ml. of the 1. O M solutions, respectively. Mixtures of all the cations were incompatible. One mixture contained Ag, Al, Ba, Cd, Ce, Cr, Co, Cu, Fe, Pb, RIg, RIn, Xi, T1, and Zn. With such a mixture, the silver ion concentration was O.05M; the concentration of the other ions was 0.025M. Berause of the high ionic concentration of this mixture, initial zones in the moist paper were formed by adding five 2-pl. portions side by side. Detection of Zones. Many ions were converted to colored sulfides by spraying the paper with yellow ammonium sulfide. These ions were placed side by side in the moist paper, e.g., Ag, T1, Pb, Cu, Cd, Fe(III), Co, Ni, Sb, Hg(I), Hg(II), As, Sn(IV), Pt(IV), Au, as shown in Figure 3. After the migration, this section of the paper was cut off and sprayed (in a hood). A fetv complexing agents, such as cyanide, prevented the formation of the colored sulfides of certain ions, particularly nickel and cobalt. Under these circumstances, it
was necessary to spray the paper 11-ith acid and to allow it to stand for several hours before addition of the sulfide. The colors of the zones are sho\m in Figure 3. Four ions, Al, Ce, Mg, and Zn, were converted to fluorescent zones by spraying their section of the paper with 8-quinolinol (0.5 gram dissolved in 60 ml. of absolute ethyl alcohol and diluted to 100 ml. with water). With acidic solutions, the fluorescence was increased by a secondary spraying with ammonia. Barium ions were located with a freshly prepared, dilute solution of potassium rhodizonate after the paper had been sprayed with acetic acid. Manganous and chromic ions were located with alkaline ammoniacal silver nitrate solution (0.l.M AgN03 in 231 NH3 mixed with an equal volume of 6 M NaOH). Hydrogen peroxide (5 pl. of a 3% solution), added to detect the electroosmosis, was located with the alkaline ammoniacal silver nitrate (14). With the paper employed in these experiments, the electro-osmotic displacement was toward the cathode, both in the weakly acidic and ammoniacal solutions (1, 14). The displacement itself was roughly one tenth the migration of the noncomplexed silver or thallium cations. The sensitivity of the sulfide test for thallous and silver ions was tested in various ways. The silver ions in as little as 2 p1. of 0.001563f solution added to dry paper were detectable; and the thallium ions in as little as 2 pl. of 0.00007811M solution were just detectable. After migration in moist paper, the sensitivity of the tests was reduced owing to the dilution of the ions in the zones. For example, zones of silver ions formed from 2 ~ 1 of. solution and migrated in ammoniacal oxalate for 4 hours a t 5 volts per cm. \\-ere detectable when the initial silver concentration was 0.025M (but not less). Under similar conditions, thallium ions were detectable down to about 0.0063M. With an initial zone of 10 pl. and similar migration conditions, silver ions were detectable when the initial concentration was O.O063X, and thallium ions were detectable when the initial concentration was 0.0016 to 0.0031V. Exploratory Experiments. I n the search for background electrolytes that would facilitate the separation of silver and thallium ions from various cations, numerous solutions were tested with the arrangements shown in Figures 2 and 3. These experiments provided a basis for selection of the most promising background solutions with the most effectiw proportions of buffer and complex-forming reagents. Separate tests were then performed to demonstrate the efficiency of the system with silver, thallium, and
silver plus thallium ions and with silver and thallium ions plus various cations. Separation of Thallium and Silver Ions from Various Cations in Acidic Solutions. Thallium ions migrated faster than silver and all polyvalent cations in acidic solutions. The precipitation of silver a t the starting point and the formation of trailing zones in many acidic solutions n-ere often prevented by ammonium salts even though the solution remained acid. A typical experimental result is shown in Figure 3. From this electrochromatogram it is evident that thallium and silver should be separated from each other and from many other cations in the lactic acid solution. and this was demonstrated by separate experiments. Separation of Silver Plus Thallium from Complexed Cations in Ammoniacal Oxalate. I n ammoniacal solutions, oxalate ions complex all polyvalent cations leaving both silver and thallium as cations. Under these conditions, the separation of silver from thallium was usually incomplete (Figure 4). These conditions serve for the separation of silver or thallium from all polyvalent cations, but they do not serve for an effective separation of silver and thallium from each other. Separation of Thallium Ions from Complexed Silver and Polyvalent Cations in Ammoniacal Oxalate Plus Cyanide. I n the presence of oxalate plus cyanide, all polyvalent cations and silver ions are converted into anionic complexes. The thallium ions remain as cations, 11-hich are readily separable from the anionic species. These separations, which can be made very quickly, are illustrated by Figures 5 and 6. At a very low concentration of the background electrolyte, the silver migrates slowly and irregularly from the initial zone (Figure 5). At a higher concentration, the silver migrates uniformly from the initial zone so that a remarkably effective separation of silver and thallium is obtained (Figure 6). Several polyvalent cations, however, also yield species that migrate rapidly as anions and that contaminate the silver. Consequently, n-ith mixtures of these cations, the cyanide plus oxalate medium provides effective separation of the thallium only. Separation of Silver Ions from Thallium and Polyvalent Cations in Ammoniacal Ammonia-Triacetic Acid. Ammonia-triacetic acid, nitrilotriacetic acid, N(CH2COOH)s,complexes polyvalent cations forming anionic chelates. I n dilute ammoniacal solution, i t also forms anionic complexes n ith silver and thallium ions. -4s the ammonia concentration is increased, the silver becomes cationic, presumably forming the ammoniated silver cation, VOL. 33, NO. 4 APRIL 1961
529
Figure 5. togrophy
Separation of thallium ions b y electrochromo-
Figure 6. tography
Separation of thallium ions b y electrochroma-
Paper moistened with 0.0125M hydrosyonis acid and 0.0125M om-
Paper moistened with 0.05M hydrocyanic acid and 0.05M ammonium
monium oxalate in 0.0463M ammonio: DH. 9.53; potentiol, 16 volts per cm.; current, 75 ma.; time, 30 mi”. Mixture 03 in Figure 4
oxalate in 0.1 85M ammonia; pH, 9.5; potentioi, 8 volts per cm.; currentl 125 ma.; time, 30 min. Mixture as in Figure 4
while the thallium remains as the ammonia-triacetic acid complex. I n the more strongly ammoniacal solutions, silver ions are readily separable from the polyvalent cations and from thallium, but thallium may be contaminated hy various polyvalent cations (Figure
7). Essentially the same results were obtained with 1,3-diamino-Z-hydroxypropane-N,N,N’,N‘-tetraacetic acid (DAHPTAA). I n a 0.02iM solution of the DAHPTAA in 0.LM ammonia (pH 9.2), both silver and thallium ions migrated toward the anode at about the same rate. I n a 0.02M solution in 0.5144 ammonia (pH 10.6), the silver ions formed a rather diffuse zone that migrated slowly to the cathode. But similar solutions in 1 . O M ammonia (pH 10.9) and in 3.0M ammonia (pH 11.4) yielded clearly defined silver zones that migrated rapidly toward the cathode leaving all the other ions as precipitates or as complex anions. Ethylenediaminetetracetic acid (EDTA), (ethylenedinitri1o)tetraacetic acid, complexed silver very strongly. With a 0.0125M solution of this reagent in 6.0M ammonia (pH 11.5), the silver ions remained at the starting point. The thallium ions migrated as anions with the complexed polyvalent ions. On the basis of these observations EDTA must complex silver much more strongly than ATA or DAHPTAA.
(Figure 7), the ammonia-triacetic acid serves as a complexing agent for all the ions. The ammonia serves as a competitive complexing agent for the silver and also as the pH buffer and reservc background electrolyte. I n all the separations reported here, the selective differential electrical migrations depend upon the relative stability and the electrical mobility of the ionic complexes. From this standpoint, these separations are not related to the usual chemical separations, which depend upon the formation of insoluble products. The procedures for the separation of silver and thallium ions from each other (Figures 6 and 7) indicate that, within the sensitivity of the detection
methods, there is no cross contamination of the zones of silver and thallium. Moreover, if one assumes that a t any moment most of these ions are in the complexed form and that any noncomplesed ions are in dynamic equilibrium with these complexed species, then, on the average, all the silver and thallium ions will be moving with the principal respective zones. Although a few of these ions may he lost in the impcrfections of the paper stabilization system and although a few may be noncomplexed a t a given moment, none of them can possibly move very far in a direction opposite t o the direction of migration of the principal zone. From this reasoning, the separation of silver and thallium ions from each other (and from the
DISCUSSION
These experiments show that complex formation may he made the hasis of selective analytical separations by differential electrical migration. I n the separation of silver from various cations 530
ANALYTICAL CHEMISTRY
Figure 7. Separation of silver ions b y electrochromatography Filter paper moistened with 0.01 25M ammonia-hiacetic acid in 3.OM ammonia; pH, 11.4; potential, 8 volts per cm.; current, 58 ma.; time, 1 hour Mixture (19 in Figure 4
other coniplesed species) should be complcte n ithout any cross contamination. The exploratory experiments were carried out with cations of elements of the principal periodic groups. -4s a consequence, the procedures described for the separation of silver and of thallium ions from very complex mixtures (Figures 6 and 7) should be useful with mixtures of virtually all cations except those of the alkali metals, which are not complexed anionically by any of the reagents tested thus far. As Evans and Strain (8) have given approlimate comparative mobilities of the alkali metal ions in solutions of acids and ammonium salts, one may estimate the location of silver and thallium ions relative t o those of the alkali metal ions. For example, the mobility of the silver ion is about 1260 in acids (1000 X em. migrated +- potential gradient X hours). That for cesium (and potassium) is 1750 and that for lithium is 1000. Consequently silver ions in acid solutions should separate with sodium
between lithium and potassium. The mobility of thallium is 1760; hence this ion should separate with potassium and cesium ahead of sodium. I n the ammoniacal oxalate solutions, silver and thallium exhibit similar mobilities (1160 and 1110) which are nearly the same as those of cesium and potassium (1200) in solutions of ammonium salts. These investigations indicate that it should be possible to develop rapid, sensitive, systematic, electrochromatographic procedures for the isolation of particular ions from complex mixtures. Should enough selective background electrolytes be found, a new, rapid, widely applicable system of analysis will have been developed. LITERATURE CITED
(1) Engelke, J. L., Strain, H. H., Wood, S. E.. ASAL. CHEY.26. 1864 (1954). (2) Evans, G. H., Strain, H. H., I & d , 28, 1560 (1956).
(3) Lederer, M., “Introduction to Pap:: Electrophoresis and Related Methods, Elsevier, Xew York, 1955.
(4) McDonald, H. J., Lappe, R. J., Marbach:‘E. P.. Spitzer, R. H., Urbin, R.1. C., Ionography. Electrophoresis in Stabilized Media,” Year Book Publishers, Chicago, Ill., 1955. ( 5 ) Ribeiro, L. P , Llitidieri, E., Affonso, 0 . R., “Electroforese em Papel e Metodos relacionados,” Servicio Grafico do I.B.G.E., Rio de Janeiro, 1958. (6) Sato, T. R., Kieieleski, W.E., Yorris, W. P., Strain, H. H., ANAL. CHEM. 25, 438 (1953). ( 7 ) Sato. T. R.. Sorris. \Ti. P..‘ Strain. ‘ H. H.,’Ibid., 26, 267 (1954). (8) Zbid., 27, 521 (1955). (9) Strain, H. H., Ibid., 31, 818 (1959). (10) Zbid.,. 32., 3R (1960); Ibid., 30. 620 (1958). (11) Strain, H. H., “Chloroplast Pigments and Chromatographic Analysis,” 32nd ilnnual Priestley Lectures, The Pennsylvania State University, University Park, Pa., 1958. (12) Strain, H. H., Sato, T. R., ANAL. CHEM.28, 687 (1956). (13) Tuckerman, M. M., Strain, H. H . , Ibid., 32, 695 (1960). (14) Wood, S. E., Strain, H. H., Ibid., 26, 1869 (1954). RECEIVEDfor review October 4, 1960. Accepted January 3, 1961. Based on work performed under the auspices of the C. S. Atomic Energ. Commission.
Use of Chlorine in Cation Exchange Separations W. J. BLAEDEL and EUGENE D. OLSEN’ Chemistry Department, University o f Wisconsin, Madison, Wis.
b Chlorination of strong acid resins results in a significant decrease in the number of sulfonic acid groups, and is accompanied b y an almost equal increase in the number of weak acid groups. Other effects of chlorination seem to b e nuclear chloride substitution and the formation of pH-sensitive chromophoric groups. The consequences of these effects in using chlorinated resins for analytical separations are discussed,
R
of metal ion species by cation exchange resins has been inferred or alluded to repeatedly in the chemical literature. For example, Fritz and Karraker (7) stated that Fe(II1) is reduced to Fe(I1) during passage through Dowex 50W, prohibiting good separation of Fe(II1) from divalent metal ions. Reduction of gold, platinum metals, and strong oxidants like dichromate, permanganate, molybdate, etc., has also been reported (4, IS). Lenskaya (9) showed that oxidizing systems Fvith oxidation potentials below 0.60 volt are not reduced by the sulfonic acid resin NSK, while systems EDVCTION
Present address, Chemistry De artnient, Franklin and Marshall Cotege, Lancaster, Pa.
with oxidation potentials above 0.77 volt are reduced. Lenskaya also claimed that the capacity of the resin was diminished by oxidation. I n attempts to prevent reduction and to improve separations, holding oxidants have been used by some workers. Thus, in separations on Dowex 50W, Blaedel, Olsen, and Buchanan (4) used chlorine as a holding oxidant for the platinum metals, and found t h a t it was necessary to pretreat the resin with chlorine in order to maintain chlorine in solution as a holding oxidant. In analytical separations on Dower; 50, AlacKevin and MeKay (11) also found chlorine necessary in maintaining iridium in the oxidized state. For separations on cation resins, chlorine appears to have advantages over other, stronger oxidants, like dichromate or permanganate. It is capable of oxidizing a good number of metals, resin-chlorine systems are fairly stable after proper pretreatment, and the small amounts of chloride formed by reduction of chlorine are usually tolerable in separation schemes (4). In spite of the apparent uscfulncss of chlorine, not much has been reported on the nature of the reaction betwen chlorine and sulfonic acid resins. Bauman, Skidmore, and Osmun (5) and later Braithwaite, D’Smico, and
Thompson (6) showed qualitatively that chlorine is adsorbed on strong acid resins, but they indicated that the properties of the resin were little affected. I n a n accelerated oxidative test with an electrolytic procedure, Frisch, McGarvey, and Moffett (6) found that although the salt-splitting capacity did not change significantly, a definite increase in the moisture content and total exchange capacity occurred. These phenomena were interpreted to be due t o a reduction in the cross linking and the formation of rveak acid groups on the ends of broken chains. These findings were not completely in accord nith early qualitative studies made in this laboratory; so a more detailed study was undertaken. This paper describes the effects of chlorine uptake by the resin upon exchange capacity, moisture content, and weak acid groups. The practical consequences of these effects on analytical separations are also discussed. EFFECTIVENESS OF CHLORINE IN PREVENTING REDUCTION OF FE(III)
A tracer sample of about 0.1 pc. of FeiIII)b6-59 in 0.0161 HCIOA was adsorbed‘ on a small column Eontaining about 20 meq. of Don-ex 50W (100-200 mesh, X8, 15 em. long and 12 mm. VOL. 33, NO. 4, APRIL 1961
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