Electrochromatographic Sequences T. R. SATO, WILLIAM P. NORRIS, and HAROLD H. STRAIN Argonne National Laboratory, Lemont, 111.
As an aid in the detection and isolation of substances by electrochromatography, the electrochromatographic sequences or relative migration rates of various cations have been determined. In solutions immobilized in paper, each ion usually yields a single migration zone. With mixtures of ions, the number of the possible sequences of the zones depends upon the number of the separable components. With mixtures of silver, nickel, and cupric ions, the observed sequences depend upon the properties of the ions themseltes, the nature and composition of the electrolytic solution, and the sorption of the ions by the paper. The separability of mixtures of some rare earths by electrochromatograph) in lactic acid solution depends upon
their selective sorption by the paper, which increases with decreasing acid concentration. The migration sequences and the direction of the migration provide clues to the condition of the ions in the solution as, for example, in the formation of complex or chelated species. The formation of complex ions that reverse the direction of migration serves for the complete or absolute separation of certain cations from mixtures, notably the separation of cupric ions from the alkaline earths. Knowledge of the electrochromatographic sequences provides a basis for the detection and identification of various cations and makes possible new analytical separations based on one-way migration and continuous electrochromatography.
S
ISCE Tswett’s chromatographic evperirnents in 1903 and
At the present stage of knowledge, there is no comprehensive basis for the prediction of the migration sequences. In the investigations summarized here, observations have been based upon the use of various empirical procedures such as arbitrary variation of the electrolytic solution, variation of the paper, and the use of various porous media. Some of the observations, such as the reversal of the migration sequences, may be utilized to effect complete or absolute separations of mixtures by one-way, twoway, or continuous electromigration ( f 2 ,19, d o ) .
1906, chromatographic sequences have served for the detection, description, and identification of a variety of soluble substances (11, 15-18). By analogy, the electrochromatographic sequences observed during the resolution of mixtures by differential electrical migration in moist porous media (12, 19, 20) should also serve as effective observational, descriptive, and interpretative aids. The effective use of thrqe electrochromatographic sequences depends on information about the number of possible migration sequences. It also depends on knowledge about the conditions that affect the sequences and the relative migration rates of the ions As a step toward the utilization of the migration sequences as aids in research, this investigation has been directed along four principal courses-the calculation of the permutations of the zones and the maximum number of the migration sequences, the determination of the conditions that affect the migration sequences, the comparison of the electrical migration or mobility of various ions, and the use of sequences in the development of analytical and separatory procedures.
PROCEDURES
One-way electrical migrations were carried out in moist paper as previously described (12, 20). Some of the migrations such as those reported in Table I were performed in paper sheets about 30 em. long and 10 to 20 em. wide. These sheets were laid across a plastic plate or pane of glass. They were moistened with the electrolytic solution and blotted with soft paper to remove the excess liquid. Solutions of the mixtures to be examined (about 50 91.) 0.001 to 0.01M) were added to small penciled regions near the center of the moist sheets, which were then covered with another pane of glass or plastic.
NUMBER OF MIGRATION SEQUElCES
With electrolytic solutions of large buffer capacity such as those containing weakly dissociated organic acids or bases, platinum or graphite electrodes were held in contact with the moist paper ( 1 2 ) . With dilute solutions of strongly dissociated electrolytes, each end of the paper and an electrode were placed in portions of the electrolytic solution. Electrical potential of 160 to 400 volts direct current ( 5 to 13 volts per centimeter) was applied to the electrodes for 2 to 4 hours. The zones of the separated ions were then located by spraying the paper with solutions of specific reagents such as dithio-oxamide in methanol. The paper commonly employed in these tests was made of wood cellulose and was 0.03 or 0.05 inch thick (Eaton-Dikeman Co., Grade 301). A few migrations \?-ere also carried out in paper made of glass fibers (Naval Research Laboratory) ( 1 2 ) . Cellulose paper was impregnated with silicic acid by dipping the paper in dilute sodium silicate, followed by extraction with nitric acid and with distilled water. Barriers of various complexforming ions were established in the paper by placing very narrow strips containing these ions across the path of the migrating mixtures (Figure 1). Some migrations were also carried out in moist chamois. Before impregnation with the electrolytic solution, the Chamois was washed in aqueous ammonia, in acetic acid, and in eater. I t was then dried in air. For comparison of the migration rates of various ions in a single electrolytic solvent, some of the migrations were performed in paper sheets about 45 cm. wide and 1 to 2 meters long. These large paper sheets were encased in thin polyethylene plastic sheets and supported on a Thermopane window through which
In conventional chromatography based upon the flow of the solvent, the number of the chromatographic zones equals the number of the separable components, n, of the mixture. The maximum number of sequences or permutations ( 1 5 ) of these chromatographic zones, Sc, is represented by the equation
s c = n(n - l)(n - 2) . . . (n - n + 1) = n! In electrochromatography, the number of the migrating zones is also equal to the number of the separable components, n. In this differential migration procedure, however, the ions may migrate toward the cathode or toward the anode (20). The sequences may, therefore, be designated by the relative location of the zones or by the location of the zones with reference to the initial location of the mixture. For mixtures of the same solutes, the maximum number of electrochromatographic sequences based upon location of the zones relative to one another, SE, is equal to the number of the chromatographic sequences, SC. But with respect to the initial location, 0, of the mixture, the maximum number of possible electrochromatographic sequences, SEO,is greater than the number of chromatographic sequences by the factor of n 1.
+
SEO =
(n
+ l ) n ( n - l)(n - 2 ) . . . ( n - + 1) = ( n + I)! 72
267
A N A L Y T I C A L CHEMISTRY
268
principal variant was the electrolytic solution. For each of the binary mixtures silver-cop + parentheses) per, silver-nickel, and copperPaper Sequence Electrolytic Solution nickel, all six sequences (Sao) have been found. For the misUntreated - A g , Ni, C u : T ture silver-copper-nickel, 14 of the 24 possible sequences hare been observed. - ( A g , Vi), C u : Chamois 0.1M lactic acid Untreated - .4g, Ni, ( C u : ) 4.11 NHa in 0.03.11 KOH plus 0.141 glycerol t When the electrolytic sohUntreated - Ag, (Xi, Cu) : 4.44 NHs in 2% diethylenetriamine: 107, pyridine in tions contained several solutes, 2% dl-a-alanine: 1 M S H 3 in 1% @-alanine the reaction between these sol4 M XHI in 0.01-M KOH Glass fiber utes and the ions being sepaUntreated 1,M S H 3 in 0.5% ammonium oxalate - Ag, Cu, S i : rated depended on the compoGlass fiber 4.M SHa - .4g, (Cu, Xi) : sition of the electrolytic soluChamois 28.11 "I; 4 M NHs tion. As shown in Table I, the Untreated - (Ag, Cu, S i : ) mobility of silver ions in amPlus silicic acid monia solution containing alaUntreated - Xi, Cu, Ag: 2% diethylenetriamine in 0.5% tartaric acid nine was not altered unless the Gntreated - (Xi, Cuj, Ag: 2% diethylenetriamine. 2% diethylenetriamine in 2% @-alanine; 2% diethylenetriamine in 2% dl-asolution was made strongly alanine. 2% dlethylenetriamine in 0.1 % Yersene alkaline, whereupon the silver Cntreated 10% pyrihine in 0.1M tartaric acid -- (Xi, Ag, Cu) : T n trea ted Ag, Xi:Cu 1% diammonium tartrate; 0.5% dipotassium tartrate migrated toward the anode. in 2% dl-o-alanine; 2% triethanolamine in 0.5po tartaric acid Similarly, the direction of the rntreated Ag, Ni(:Cu) 1.W SHa in 0 5 5 diaramonium tartrate migration of copper and nickel Untreated 0 . l M KOII in 0.l.U dl-a-alanine - (pii, Cu):.4g ions in solutions of many polyUntreated - Cu. ( S i : ) A g 1% (CHs)aSOH in 1y0@-alanine basic acids was gradually reUntreated Ag:Ni. Cu 1 % dipotassium tartrate: 2$: triethanolaniine in 0 :% versed as the solutions were citric acid Untreated &:(Si,C u j 2%- triethylamine and 0.5% citric acid in saturated made alkaline with potassium soln. of Versene; 0.1% Versene in 4 M NHa Untreated 441 S H I in 0.2% ammonia triacetic acid; I . M , S I l r in A g : C u , Xi hydroxide or with tetranieth0.2% ammonia triacetic acid pliis 2% trlethitnol ylammonium hydroxide. I t aniine one point in the course of this C u : ( X i , .4g) Untreated 2% triethanoIamine in 1 % dl-a-alanine Untreated (Cu:)(Ag, Xi) 0.1M KOH in 0.5M dl-a-alanine reversal, each ion formed a Untreated : C n , Ni, Ag 2% triethylamine in 0.5% dl-a-alanine plus O.": stationary zone in the migratartaric acid: 2% triethylamine in 0.5% dl-a-alanine plus 0.5% tartaric acid plus 0.2% KOH tion system. Under all these -L rntreated :Ag, Cu, Si-, , 2% triethanolamine in 0.2% ammonia triacetic arid Untreated :Ag, (CU, hi) T 0 4% K C N in 0.4% KOH and 4.11 SIII; 0.47, K C S in migration conditions, the eo112% diethylenetriamine per and the nickel ions foimed Untreated Mixture in KC?\' electrolyzed in 4.1.I NHa : ( A g , S i , Cu) + but one zone each. Migration sequences of the rare earth elements, some of cooling water was circulated. Details regarding the construewhich have already been reported (4, Sj,varled with the concenOf tion and the use of this apparatus for the tration of the electrolytic solution as well as with the nature of the and phosphate ions have been reported (I, 7 ) . SIigrations in electrolyte. In lactic acid, for example, the *parability of scanthese long paper strips required 0.5 to 2 days. The zones of the separated ions were located through the use of radioactive dium from cerium was greatest in dilute acid, Chromatographic tracers (19). When ions of high mobility and ions of low mobility experiments summarized in Table I1 show that the sorbability were present in a fixture, the &ration was interrupted after and the separability of these ions increased with the dilution of 6 to 12 hours. A large portion of the paper containing the ions the lactic acid. At Very ]OW concentrations of lactic acid, the of high mohilitv was removed and reDlaced with fresh]\- moistened papi;: and- the electrolysis was continued until the -ions of low ions migrated very s l o d y , and the zones became elongated, so mobility were separated from one another. The continuous separation of mixtures by electrical migration transverse to the flow of the electrolytic solution &-asperformed in porous paper 0.1 inch thick and 12 inches s uare (8). These separations were also followed by the use of rajioactive tracers. Table I.
Electrochromatographic Sequences of Silver, Nickel, and Copper Ions (Electrodes indicated b y and -, starting point indicated by :, incompletely separated zones included in
+ +
+ + + ++ ++
+ + ++ + + ++ +
-
The separability and sequences of some ions such as silver, nickel, and copper were determined in a great variety of electrolytic solutions. With other ions, such as those of the heavy metals, solubility effects limited the variation of the solvent. The sorbability of some of the ions by paper was determined by chromatography. The solution, added as a narrow zone in a paper strip, was washed by downward flow of the solvent in a closed cabinet ( 7 ) . The proportion of the ions remaining i n solution in the migrating zone equals the R value, the ratio of the distance traversed by the solute to the distance traversed by the
ing boundary, Rr. RESULTS
Sequences of Silver, Nickel, and Copper Ions. The sequences observed in various solutions are summarized in Tahle I. The
t
8:
Initial location of ions Final position of ions Formulas indicate constituents of added mixtures Strontium is located with sodium rhodizonate, copper with dithio-oxamide 24 volt8 per centimeter for 40 minutes
V O L U M E 26, NO. 2, F E B R U A R Y 1 9 5 4
269
Figure 2. In this one-way migration experiment, mineral acid in the zirconium and niobium preparations caused slight distortion of the phosphate (Pa2)and calcium zones. I n similar experiments in which the zirconium and niobium solutions were stabilbed with oxalic mid, the zones of these elements became diffuse and migrated b Nard the anode. The farther the ions migrated, the greater the separation of the zones from one another. -4lthough the separation of yttrium from cerium was scarely detectable after migration for 6 hours, continued migration reFigure 2. O m - w a j mecrromigrauon or varlous ions m raper lVlo&stenOdW i t h sulted in aeamplete separation of these 0.1M Lactic Aoid tN0 ions, the yttrium migrating the Migration time, 6 hours faster. Niobium and zirconium were in rolution i n strong mineral acid which distorted the P04(P*1) zone Comparison of the migration of . Startin. line to cesivm was 59 Em. (6 rolts per oentimeter, 20 ma.) yttrium and cerium ions in the same strip of paper revealed that the rates of separation and of migration increased far about 10 hours, as Table 11. Effect of Eleotrolyte Concentration on Chroshown by Figure 3. In additional one-way experiments, mixtures matographic Migration of S c a n d i u m and Cerium of yttrium isotopes xere allowed to migrate, and after the paper conon. of had been dried, autographs were prepared as the isotopes decayed. LBOtiO Acid, Scandium Cerium Under these conditions both isotopes were found uniformly disMa db,crn RF" RTd d.am. HP RT tributed in the migration zone. 2.0 27.2 1.00 1.00 29.5 1.00 1.00 The causes for the variation of the migration rates of cerium 1.0 32.3 1.00 1.00 32.8 1.00 0.57 0.3 34.7 1.00 0.97 36.1 1.00 0.50 and yttrium during the electrolysis (Figure 3 ) are not apparent. 0.25 37.4 1.m 0.95 36.0 0.83 0.19 0.10 The differences between the migration rates of the yttrium iso34.7 0 . 8 8 ' 0.32 37.0 0.22 0.03 topes are within the experimental variation. i w = molality. 6 d = migration of laotic soid solvent, in oentirnetera. With chemical reagents (80) as well 8 8 with radioactive tracers ' R r = relative migration of frontal boundaries of chromatographic =""afor location of the sones, experiments similar to that illustrated d RT = reiatiw migration of tr&iiing boundariea of ehrmnstographie by Figure 2 have provided the migration sequence of a number of zOne8. ions in 0.1M lactic acid ( 6 , 8, 20). The sequence of the zone8 in the order of decreasing mobility was: Cs Rb, TI, Ra. Ba Sr Ca, Cd: Co, Ni Zn, Pb, Cu, YQo Y9' Nd, Ce P m that separations were impractical. I n ammonium tartrate Pr + Eu, S r TT T h Ri Pn solutions (about 0.05.M), the separability and the sequence of the rare earths varied with the proportions of the ammonium and tart,rate ions, hut in these solutions the rare earths were not sorbed by the paper, R = 1 . Composition of Mixture. The mixtures that were submitted t o electromigration sometimes had remarkable effects upon the migration of the ions, upon the sequences, and upon the definition I of the migrating zones (7). The effects of a little cyanide and of an excess of cyanide upon the migration of cupric ions in ammonia 8olution are shown in Figure 1. Similar effects were observed when ammonia triarrtic acid was added to solutions of capper and nickel ions before esamimtion by electrolysirr in ammonia solutions. The migration of the copper and nickel ions toward the mode decreased nit,h decreasing amounts of the ammonia. Figure 3. VariationofMigrationof Cerium Ions and trincetio acid. I t did not occur in electrolytic solutions of orY t t r i u m Isott,pes in 0.1M Lactic Acid giinic acids. Effect of 3 Barrier. The effect of a harrier of cyanide ions on the migration of cupric ions in ammoniacal solution and the lack. With the electrodes on the paper so that there was no electroof an effect of these ions upon the migration of strontium ions osmotic flow (7), many ions did not migrate in laotio acid soluare illustrat~din Figure 1. Silver and nickel ions migrated like tions, as, for example, mercury (IT), arsenic, niobium, zirconium, cupric ions. Barium and calcium ions and alkali metal ions hafnium, bismuth, and antimony. The polonium by contrast migrated through the cyanide barrier. migrated S I O N I ~toward the mode. With the ends of the paper The following sequence of the ions was observed in 4M amin the electrolytic solution, the electro-osmotic flow (7) carried monia with a cyanide harrier: (barium, strontium, oalcium): the bismuth toward the cathode and caused the polonium to silver, nickel, copper. Separate chromatographic experiments remain a t the point of addition. Some of these ions that are showed that cupric ions were strongly sorbed by paper from soluinsepartreble in lactic acid were readily separable in other election in ammonia, hut cuprous cyanide was not sorbed under these trolyte solutions. Their separability also varied with their conditions. The sorbed cupric ions were rapidly eluted with concentration. nmmonis. solution containing cyanide. I n the lactic acid solution, most ions formed a single, wellMigration Rates of Radioactive Ions. Relative migration rates defined migration aone. Ruthenium, by contrast, formed eight of various radioactive ions in lactic acid solution are shown in or more zones, half of which migrated to the anode.
+
+
+
+
+
+ + + +
ANALYTICAL CHEMISTRY
210
Through chemical reaction, some ions formed diffuse zones. Ferric ions, for example, yielded a long diffuse zone extending from the initial location of the mixture toward the cathode. Silver ions farmed a diffuse zone because of reaction with impurities in the paper (18). For short migration distances, the zone of silver ions appeared between the eones of thallium aud barium. In 0.1M lactic acid, uranium (UP3*),plutonium (Pua$Q),and ionium (Thaaa), a t tracer levels, separated slowly in the sequence U, Pu, Io. The plutonium aoue was long and extended into both the uranium and the ionium zones. The separation of uranium from ionium WBS complete in about 24 hours, in which time the uranium had migrated 20 om. ( 5 volts per centimeter). With lactic acid as the electrolytic solvent, uranium (0.01M) separated from thorium (0.01M) in about 1 hour (22 Volt8 per centimeter) and formed the leading zone. Both uranium and thorium were readily separable from zirconium and from hafnium, which migrated slightly toward the anode a t the leading boundary. Migration in lactic mid also served for the separation of radium from its decay products. The radium migrated faster than lead and lead migrated much faster than bismuth, which migrated dowly away from the polonium. This migration procedure has also been utilized for the separation of radioactive lead, bismuth, and polonium derived from radon. Effect of Organic Acids. Solutions of various organic acids altered the sequences and the separability of thorium, uranyl, and zirconyl ions. I n 0.lM solutions of many acids, uranyl ions migrated rapidly toward the cathode, the thorium ions migrsted slowly toward the cathode, and the zirconyl ions did not migrate or eke formed diffuse zone8 extending toward the anode. These effects were observed in formic, glycolic, gluconic, lactic, malonic, succinic, and ohloraacetic acids. I n tartaric acid, both the aircony1 and thorium ions formed diffuse cones migrating towasd the anode. I n ox& acid by contrast, the zirconyl ions formed a well-defined zone that migrated rapidly toward the anode followed by uranium and then by thorium, the latter remaining near the starting point. Continuous Separations. Continuous electrochromatographic separations of calcium and phosphate ions, of silver and chromate ions, and of strontium and yttrium ions have been portrayed photographically (1, 8). Additional radioautographs have now shown that many mixtures of ions may be resolved continuously by the flow of solvent transverse to the electrical potential, In O.1M lactic acid, strontium, yttrium, and phosphate ions have been separated from one another, and calcium, yttrium, and phosphate have also been separated. Both strontium and calcium migrated faster than yttrium, as would be predicted from the sequence in the one-way migration (80). Mixtures of strontium and oalcium were not separated by the continuous procedure, and mixtures of the yttrium isotopes (Ynoand Y99 were not sepmated. A mixture of four components, strontium, yttrium, cerium, and phosphate ions, was resolved continuously, the displacement of the cerium by electrical migration being slightly less than that of the yttrium. A mixture with the five components, cesium, strontium, yttrium, cobalt, and phosphate, was easily resolved continuously, the cobalt forming 8. zone hetween the yttrium and the phosphate zones (17). A mixture with six components has also been resolved continuously, providing the series of zones illustrated in Figure 4. In this separation, the zones of.niobium and airconium gradually became dense, owing apparently to the formation of colloidal hydroxides. To circumvent the high coat of the organic electrolytes widely used in the continuous electrochromatography (6,8, SO), minerd acids have now been employed a t low concentration (about 0.01M) and have been found t o yield effective separations similar to those obtained with lactic acid. A typical one-way sequence in nitric acid was: silver, nickel, copper, uranium, thorium, zirconium. With many acids, the products of the
electrode reaotions did not interfere with the separations in the cell so that separate electrode compartments ( 8 ) were not required. DISCUSSION
The variations of the electrochromatographic sequences (Tahle I, Figure 1) are dependent upon the composition of the electrolytic solution aud upon the nature and treatment of the porous support. The mechanism of these varibtions is related to many effects, such as the formation of complex ions in the electrolytic solution, the variation of the activity or degree of dissociation of the migrating ions, the alteration of the oxidation state, and the variation of t h e sorption of the ions hy the porous support. With variation of the electrolytic solutions, one or more of these mechanisms may predominate, but several may play distinctive roles.
Nbs5
Figure 4. Autograph of Paths Followed by Cesium, Strontium, Yttrium, Uranium, Zirconium, and Niobium in Continuous Eleotroehromatographie Cell 0.1M lsctio acid, 40 wlfs, 200 ma.
'
When the direotion of the migration of ions varies with the pH of the electrolytic solution, as with copper ions in tartrate or ammonia triacetie acid solutions, there must be a t least two ionic species of the migrating substance. The net electrical charge on these two species must be of opposite sign. There must also be a rapid, dynamic equilibrium among the species; if there were not, separate zone8 should be formed. Electrical migration in solutions containing various oomplexforming reagents may be made the basis of widely applicable, analytical metbods. The reversal of sequences, as shown in Tahle I and in Figure 1, may Serve for the absolute separation of ions, especially those ions that can be made t o migrate in opposite directions (11, 19, SO). With ions that are weakly sorbed by the paper, the sequence and the separability observed in oneway electrical migration (Figure 2) serve as a basis for prediction of the separability of ions by continuous electrochromatography (SO). Ions that were readily separable by the one-way migration method were readily sepamhle in the same sequence by the continuous method (Figure 4). With ions that are sorbed by the paper, both the sequence obtained by flow of solvent and the sequence obtained by one-
V O L U M E 26, NO. 2, F E B R U A R Y 1 9 5 4 , way electrical migration determine the sequence and the separability of the ions in the continuous method. When the chromatographic and the electrochromatographic sequences are the same, the continuous electrochromatographic method is less effective than either of the component methods. When the chromatographic and the electrochromatographic sequences are the inverse of each other, the continuous method may be more effective than either of the component methods. In the light of these considerations and in view of the variations of sequence reported in Table I, there are many possibilities for improvements in the application of the continuous electrochromatographic method. In conventional chromatography based upon the flow of solvent, a single substance has sometimes been found to yield two or more zones in the chromatographic system (3-6, 9, 10, 1 4 ) , an effect usually attributed to variation of the sorptive system or to modification of the solute. In electrochromatography, double zone formation has been found when various stable complex forms of an ion are present in the solution (Figure 1) ( 1 2 ) . Depending upon the point of view of the investigator, these double zones may be regarded as evidence for the presence of several substances in the solution or as evidence of niultiple zones of the particular element. These observations show that the electrochromatographic comparison of substances, like the usual chromatographic comparison, should be preceded by separate migration tests on each preparation ( I S ) . All these observations show that chromatography and electrochromatography are exceptionally sensitive and versatile analytical tools. Knowledge of the migration sequences of various solutes extends the applicability of both methods in the field
271
of analytical chemistry. This information often provides clues to the condition of the ions in the solutions. LITERATURE CITED
Chem. Eng. N e w s , 30, 4244 (1952). Grassmann, W., lVuturwissenschaften, 38, 200 (1951). Laskowski, D. E., and McCrone, W. C., ANAL. CHEM.,23, 1579 (1951). Lederer, hl., Compt. rend., 256, 200 (1953). Ovenston, T. C. J., Nature, 169,924 (1952). Sato, T. R., Diamond, H., Norris, W. P., and Strain, H. H., J . Am. C h e m Soc., 74, 6154 (1952). Sato, T. R., Kisieleski, W., Xorris, W. P., and Strain, H. H., A s ~ L .CHEM.,25, 438 (1953). Sato, T. R., Xorris, W. P., and Strain, H. H., Ibid., 24, 776 (1952); U. S. Atomic Energy Commission, ANL-4724 (November 1951). Schroeder, W. A., Ann. S.Y . Acad. Sci., 49, 205, 211 (1948). Smith, E. L., Nature, 169, 60 (1952). Strain, H. H., i i l v . 4 ~ . CHEM.,23,25 (1951). IEid.,24, 356 (1952).
Strain, H. H., “Chromatographic Adsorption Analysis,” New York, Interscience Publishers, Inc., 1942. Strain, H. H., I n d . Eng. Chem., 42, 1307 (1950). Strain, H. H I IND.ENG.CHEW.,ASAL. ED., 18, 605 (1946). Strain, H. H., J . Am. Chem. Soc., 70, 588 (1948). Strain, H. H., Technion Yearbook. 11. 85 (1952-63). (18) Strain, H. H., Manning, W. Sf., and Hardin, G., B i d . Bull., 86, 169 (1944). (19) Strain, H. H., and Murphy, G. W., ANAL.CHEM.,24,50 (1952). (20) Strain, H. H., and Sullivan, J. C., Ibid., 23, 816 (1951). RECEIVEDfor review July 20, 1953. Accepted November 4, 1953. Presented in part before the Division of Biological Chemistry a t the 124th MeetCHEMICAL SOCIETY, Chicago, Ill., 1953 ing of the AMERICAX
Polarography of Certain Organic Polysulfides J.
H. KARCHMER and
MARJORIE
T. WALKER
Refining Department, Research and Development Diviu’on, Humble O i l & Refining Co,, Baytown, Tex.
The polarography of dibenzyl, di-n-butyl, and ditert-butyl trisulfides and the corresponding tetrasulfides has been compared with the related disulfides. In a supporting electrolyte-solvent of benzenemethanol, made 0.1N with respect to sodium acetate and acetic acid, all these tetrasulfides and the dibenzyl trisulfide produced three polarographic waves when the dropping mercury electrode was made negative and the applied voltage was increased in a negative direction. While the half-wave potentials of these waves vary with the substituent hydrocarbon group and the number of sulfur atoms, they are sufficiently similar to form a unique polarographic pattern that is useful for analytical purposes. The early wave does not increase a t cell concentrations above approximately 8 X lo-* millimole per liter, while the intermediate wave does not appear below this concentration. Although the cur-
T
HE determination of organic polysulfides is of interest to the petroleum industry because of the deleterious effects attributed to this class of sulfur compounds upon product quality and upon refinery equipment. For example, di-tert-butyl tetrasulfide is known to repress the octane number of leaded fuels to a greater extent than most other sulfur compounds and certain polysulfides are thought to be responsible for excessive corrosion ,of equipment. Polysulfides are objectionable components of fuels, because they are readily decomposed by heat, liberating hydrogen sulfide and other products which may be undesirable from the standpoint of product quality.
rent yielded by the late wave (or the sum of its two component parts observed a t high concentrations) is proportional to the concentration of the polysulfide, the current-concentration quotients, i / C , of different compounds vary considerably; thus “tetrasulfide functional group” can be determined only semiquantitatively. While the di-n-butyl and di-tert-butyl trisulfides in some respects were similar to the disulfides, they possessed a wave in a position similar to the late wave of the tetrasulfides. Studies of the effects of varying the pH and mercury pressure and the influence of sunlight on the polysulfide gave information on the number of electrons and protons entering the electrode reactions and the types of the various waves. To explain the anomalous behavior of the first two waves i t is postulated that they are produced by reduction of free radicals t h a t exist in the solutions.
Not many methods are available for the determination of mixtures of organic polysulfides when they occur in minor amounts in hydrocarbon fractions. Mapstone ( 1 5 ) reported that a qualitative test for polysulfides could be carried out by use of an alcoholic silver nitrate reagent. Arnold, Lien, and Alm ( I ) have indicated that lithium aluminum hydride can reduce trisulfides to mercap’tans (thiols) and hydrogen sulfide, which can be determined for the estimation of the original polysulfide content. Polarograms of di-tert-butyl tetrasulfide in a mixture of methanol and benzene reported by Hall (8) revealed a unique
