product from the tube with 0.12N hydrochloric acid. The combined solution was transferred to a distillation unit (15)and sulfur dioxide was removed by boiling under reduced pressure, using a good water suction. Two methods were used for separating the six platinum metals from this solution. Osmium and ruthenium were distilled from one sample for 2 hours b y 200 ml. of perchloric acid and collected in 3% cold hydrogen peroxide. The trap was boiled for 30 minutes with 15 ml. of perchloric acid. Osmium was separated from ruthenium by the method of Westland and Beamish (15) and determined gravimetrically b y thionalide ( 7 ) . Ruthenium was distilled by oxidation in 10 ml. of concentrated sulfuric acid and 20 ml. of 10% sodium bromate and collected and determined spectrophotometrically by a method previously reported (1%'). The method of analyzing the perchloric acid pot liquid is described above. By the second process the chlorination product of Tasmanian iridosmine as obtained above was treated by the method of Westland and Beamish (16) for the separation of osmium, rutheniurn, and the base metals from platinum, palladium, rhodium, and iridium. However, osmium was collected in hydrobromic acid ( l a ) and determined gravimetrically by thionalide ( 7 ) and ruthenium was collected in a 1 t o 2 hydrochloric acid solution containing 3%
hydrogen peroxide and determined spectrophotometrically by the anthranilic acid method (la). The solution containing platinum, palladium, rhodium, and iridium, free from any base metals, was evaporated t o dryness in the presence of 2 ml. of 2% sodium chloride. Organic matter from the ion exchange column was destroyed by nitric acid and hydrogen peroxide. The small amount of sulfuric acid remaining was removed b y first fuming and then evaporating to dryness several times on a hot plate with concentrated hydrochloric acid. The chloride residue was then transferred to a 50-ml. separatory funnel b y washing with 5 ml. of concentrated hydrochloric acid and 10 ml. of water and the separations and determinations of platinum, palladium, rhodium, and iridium were carried out by solvent extraction and copper powder reduction techniques as described above. The results are included in Table 11. ACKNOWLEDGMENT
The authors are grateful to the National Research Council for financial support and t o C. L. Lewis, Falconbridge Kickel Mines, Richvale, Ontario, for carrying out the qualitative spectrographic analysis of the two iridosmine samples.
LITERATURE CITED
(1) Barefoot, R. R., McDonnell, W. J., Beamish, F. E., ANAL.CHEM.23, 514 (lW51). (2) Beamish, F. E., Scott, M., IXD.ENC. CHEM., ,4NAL. ED. 9, 460 (1937). (3) Berman. S. S., McBrvde,' JT7. $. E.. . Anaiyst si, 566 (i956). " (4) Currah, J. E., McBryde, W. A. E., Cruickshank, 8. J., Beamish, F. E., ISD. ESG. CHEM., ANAL.ED. 18, 120 (1946). (5) Gilchrist, R., Wichers, E., J . ,477~. Chem. SOC.57,2565 (1935). (61 ~, Hill. M. A.. Beamish. F. E.. ASAL. CHEM.22,590'( 1950). ' \ - - - - I
(i) Hoffman, I., Schweitzer, J. E., Ryan, D. E., Beamish, F. E., Ibid., 25, 1091 (1953). (8) Iiavanagh, J. M., Beamish, F. E., Ibid., 32, 490 (1960). (9) Marks, A. G., Beamish, F. E., Ibid., 30,1464 (1958). ( I O ) Plummer, M. E. V., Beamish, F. E., Ibid., 31, 1141 (1959). (111 Sant. B. R.. Beamish. F. E.. Zbid.. ' 33,30411961).' (12) Sen Gupta, J. G., Beamish, F. E., communicated t o Am. Mineralvgzst for publication. (13) Tertipis, G. G., Beamish, F. E., ANAL. CHEM. 32,486 (1960). (141 Westland. A. D.. Beamish. F. E.. ' Am. Minerahgist 43,' 503 (1958). (15) Westland, A. D., Beamish, F. E., ASAL.CHEW26,739 (1984). (16) Ibid., 30, 414 (1958). (17) Yoe, J. H., Kirkland, J. J., Ibid., 26,1335, 1340 (1954). RECEIVEDfor review August 15, 1962. Bccepted October 4, 1962.
A Complete Separation of a Mixture of Zi rco nium(IV), Copper(I I), Molybdenum(VI), Titu nium(IV), Vu nud ium(IV), and Magnesium(l1) by Ion Exchange Chromatography CARL MICHAELIS, SYLVESTER EVESLAGE, PAUL COULTER,' and JOHN FORTMAN2 Chemisfry Department, University of Dayton, Dayton, Ohio
b A detailed method of separation of a mixture of Zr(lV), Cu(ll), Mo(VI), Ti(lV), V(IV), and Mg(ll) on Dowex cation and anion exchange resins using hydrochloric acid elution is reported. The titanium, vanadium, and magnesium were not retained by the anion exchange resin, but the zirconium, copper, and molybdenum which form the anionic chloro complexes were. After the titanium, vanadium, and magnesium were washed from the anion exchange column with 9M hydrochloric acid, this mixture was made 11M in acid and passed through the same column. The titanium was now retained while the other two passed through. The vanadium and magnesium were then separated on the cation exchange column. The zirconium, copper, and molybdenum were successively eluted from the anion exchange column by 1764
ANALYTICAL CHEMISTRY
selecting the proper concentration of eluting acid. Elution curves were prepared for zirconium, copper, molybdenum, magnesium, and vanadium.
Mu::
has been done recently ion exchange separation of metals (8), especially those which make up complex alloy steels and high temperature alloys which are useful for supersonic air craft, guided missiles, rockets, etc. These alloys are made up of titanium, molybdenum, zirconium, vanadium, copper, and magnesium among other metals. The problems of separation for analyses are well known. Frequently ion exchange chromatography affords a convenient method of separation. Many complexing agents such as HF ( I S ) , oxalates ( l a ) ,etc., have been used WORK
in separating these metals. The procedure described here uses only hydrochloric acid to separate all six metals consecutively. It has been shown that Zr(IV), Cu(II), and Mo(V1) in concentrated hydrochloric acid solutions are strongly adsorbed by anion exchange resins (4, 6, 9). Magnesium(i1) and V(IV) do not form stable anionic chloro complexes, and Kraus and coworkers (7) have sh0n.n that Ti(1V) forms a stable anionic chloro complex in hydrochloric acid concentrations of 1OM or greater. Therefore by passing a mixture of the 1 Present address, Chemistry Department, University of Kansas, Lawrence, Kan. 2 Present address, Chemistry Department, University of Notre Dame, South Bend, Ind.
a 30 t J
s
20
0
0
50
100
150
200
230
300
3,o
,oo
.50
LOO
a,,
eo0
ML
Figure 1 . Elution curves of Zr(lV) and Cu(ll) on Dowex 1 X 2, anion exchange resin, with 6M hydrochloric acid
six metallic ions in 9-11 hydrochloric acid through an anion exchange column, the mixture ~ o u l dbe separated into two g r o i i p of three metals each. Elution curves were prepared for Zr(IV), Cu(II), l\lo(VI) ( g ) , T‘(IV), and MglII).
of eluent was required to start the zirconium coming through in the effluent, and approximately 160 ml. were required t o elute i t . The elution was continued with the same acid, and after the passing of another 50 ml. (210 ml. total), the copper began t o come through. After 550 ml. of total elution, the copper was eluted from the column.
per, and magnesium were separated exactly as described above. The titanium-vanadium-magnesium fraction was evaporated t o reduce volume and made 11X in hydrochloric acid. This mixture was then passed through the same column again. The titanium was retained by the resin and the magnesium-vanadium fraction was washed out with 100 ml. of 1251 acid. The titanium was eluted with dilute acid. The V(IV) and LIg(I1) fraction was evaporated to 5 ml., diluted with 50 ml. of distilled water to reducc. acidity, and then added to a ration exchange column containing 40 grams of resin. The V(IV) was eluted with 450 ml. of 1N hydrochloric acid and the magnesium with 100 ml. of 451 acid. The six metallic ions were successfully separated and recovered quantitatively. DISCUSSION
It was necessary to add a little concentrated hydrochloric acid t o the mixture of the six different ions before e\ aporation t o keep them all in solution when the volume was reduced to 20 ml. The volume was reduced so that, after making the solution 9.1.1 in acid, the volume would still be small. A large volume would cause the zirconium to come through before the titaniummagnesium - vanadium fraction was removed from the anion exchange column. As shown in Figure 1, there is a spread of about 50 ml. between the zirconium and the copper which affords a good separation. The molybdenum complex was adsorbed quite strongly and was eluted with dilute acid (9). After the elution of the zirconium from the anion exchange column, the Cu(I1) can be eluted quickly with 4M acid as 60 ml. of this eluent starts the copper coming through and 260 ml. completely elutes it. Figure 2 shows the elution curve of V(1V) with 1.5M hydrochloric acid on the cation exchange column containing 40 grams of the resin. Figure 3 shows the elution curve of Rlg(I1) with 1.0-If acid on the cation exchange column containing 25 grams of resin. The problem is to get the vanadium eluted before the magnesium begins to come through. T h e 1 . O M acid will separate the V(IV) from RIg(I1) using the larger quantity
EXPERIMENTAL
Apparatus and Reagents. The app:iratus was t h a t previously described ( , ‘ j ) except that 30 grams of Dowex 1 11:I< used in the anion exchange column, arid 40 grams of Ilowex 50 in the cation exchange column. Reagent grade chemicals were used throughout. T h r titanium was obtained 3 5 TiCI, from Fisher Scientific Co.; the copper as CuCl2.4H20, and the magnesium as llgC12.6H20 from 13:rker and =Idamson; the molybdenum as 1100,and the zirconium as ZrOC12.8Hz0 from Matheson Coleman and Bell: the vanadium as V2Os from -4.D. RIacKa>.Co. The titanium tetrachloride solution must be prepared with caution as the reaction of TiC14 with water is vigorous giving off clouds of “smoke.” The vanadium pentoxide was dissolved in a small quantity of concentrated hydrochloric acid and then heated vrith S a B r t o complete the reduction o f vanadium to V(1V). The analyses were done on a Bauscli and Lornb Spectronic 20 spectrophotometer. The molybdenum analyses m-ere done by the method of Ellis and Olson ( I : the titanium analyses by the method of Hastings, McClarity, and Broderick 13) ; the magnesium analyses by the method of Harvey, Komarmy, arid Wyatt (2); the vanadium analyses by the method of Karchmer ( 5 ) ; the zirconiurn hy the method of Silverman and Hawley (10); the copper analyses by the m ~ t l i o dof Snell ( 1 1 ) . Procedure. Throughout t h e investigation, carefully pipetted 10-ml. aliquots of 0.105f ion stock solutions were used to prepare t h e mixture for separation on t h e ion exchange columns. Quantities (10 ml. each) of 0.10M Zr(IV), CuiII), and Mo(V1) were made 9JI in hydrochloric acid and added t o the anion exchange column after i t was rinsed with concentrated hydrochloric w i d . After the solution had entered t h e resin, the zirconium was eluted with (iJI hydrochloric acid. About 25 ml.
Figure 2. Elution curve of V(IV) on Dowex 50 X 8, cation exchange resin (40grams), with 1.5M hydrochloric acid
The molybdenum was then eluted with 800 ml. of 1.OM hydrochloric acid (9). Next a mixture of 10 ml. each of 0.1M Zr(IV), Cu(II), Mo(VI), Ti(IV), V(IV), and Mg(I1) was evaporated to 20 ml. and made 9111 in hydrocliloric acid and added to the anion exchange column. After this mixture had entered the resin, the titanium-magnesium-vanadium fraction was washed from the column with 100 ml. of 9 V hydrochloric acid. The zirconium, cop-
0
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500
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Figure 3. Elution of Mg(l1) on Dowex 50 change resin, with 1.OM hydrochloric acid
X 8,
cation ex-
VOL. 34, NO. 13, DECEMBER 1962
1765
of resin; however, the magnesium comes through in the effluent soon after the vanadium is eluted. LITERATURE CITED
(1) Ellis, Roscoe, Jr., Olson, R . V., ANAL. CHEnl. 22, 328-30 (1950). ( 2 ) Harvey, A. E., Kormarmy, J. M.,
Wyatt, G. M., Ibid., 25! 498-500 (1953). (3) Hastings, J., hfcclarity, T. A., Broderick, E . J., Zbid., 26, 379-81 (1954). (4) Huffman, E. H., Iddings, G. M., Lilly, R. C., J. Am. Chem. SOC.73, 4474-5 (1951).
(5) Karchmer, J. H., Proc. Am. Petrol. Inst., Sect. 111 29, b3: 72-8 (1949). (6) Kraus, K. A., Moore, G. E., J . Am. Chem. SOC.75, 1460 (1953). ( 7 ) Kraus, K. A., Nelson, F., Smith, C . W., J . Phys. Chem. 58, 11-17 (1954). (8) Kunin, Robert, “Ion Exchange Resins,” 2nd ed., Wiley, Neb.- York f1958). (9) Michaelis, C. I., Tarlano, N. S., Clune, J., Yolles, R. S., ANAL. CHEnf. 34, 1425-6 (1962). (10) Silverman, L., Hamley, D. W., Ibid., 28, 806-8 (1956).
(11) Snell, F. D., “Colorimetric hIet,hods of Analysis” Vol. IIA, p. 63, Van Nostrand, N. Y., 1959. (12) Walter, R. D., J . Inorg. Nucl. Chem. 6 , 58-62 (1958). (13) Woods, P. H., Cockerell, L. D., J . A m . Chem. Soc. 80, 1534-6 (1958).
RECEIVEDfor review March 19, 1962. Accepted October 8, 1962. Work done on contract with the Aeronautical Research Laboratory of the Air Force, Research Division, Wright-Patterson, Air Force Base, Ohio.
Alizarin Acid Black SN as a Metallochromic Indicator for Calcium Nature and Stability of Its Calcium Chelates GLENN ROSS,’ DAVID A. AIKENS? and CHARLES N. REILLEY Deparfmenf of Cbemisfry, Universify of North Carolina, Chapel Hill, N. C. ,The nature and stability of the calcium chelates of Alizarin Acid Black SN, an excellent and unusual metallochromic indicator for calcium, are established directly with the aid of calcium buffers. The reaction of the indicator with calcium is complex. Two major complexes exist: a red species, CazZz, stable above pH 11 and pCa 4, and a purple-blue species, CazZ, stable below pCa 4. These account for the dual color change observed with the indicator in chelometric titrations. Two other species, probably CaHZ and CaZ, exist under restricted conditions and could not be characterized quantitatively. The behavior of the indicator with calcium is summarized in a pCa-pH diagram which predicts the color behavior of the indicator and allows selection of appropriate titration conditions.
A
Acid Black SN, AABSX, (2.1.21725, Mordant Black 25 ( I ) , 2-(l-azo-2-naphthol)-6- (1-azo-2- naphthol-6-sulfonic czcid)phenol-4-sulfonic acid, LAIZRIN
is a n interesting and unusual metallochromic indicator which gives two distinct color changes in the chelometric determination of calcium with (ethylene1766
ANALYTICAL CHEMISTRY
dinitri1o)tetraacetic acid. The dual color change was first observed b y Belcher, Close, and West (2) in the titration of 0.01M calcium at p H 11.5 t o 12.5. They reported that the indicator changed from purple-blue to red about 90% through the titration and the equivalence point was marked by a remarkably sharp color change from red to clear blue. I n titrations of 0.1X calcium, however, the end poirit color change was reported to be from purple-blue to blue. On the basis of mole ratio studies, Close and West (5) suggested that the red complex formed at low calcium concentrations is CaZz, while the purple-blue complex formed a t high calcium concentrations is CaZ. AABSN is represented by Z throughout this discussion (with the charges omitted). Close and West present a striking example of the complicated behavior possible with metallochromic indicators. Obviously, the reaction of AABSN u-ith calcium is far more involved than that predicted by the often-cited analogy between metal complex formation and acid-base reactions. More intensive examination reveals an even more involved situation. To establish the optimal conditions for the use of this unusual indicator a detailed study has been made of the stability and nature of the calcium complexes of AABSN with the aid of calcium buffers. The calcium buffer proved to be a n estremely useful tool. It allowed direct study of the formation of the red complex, which is impossible b y any other method. I n contrast to the conclusions of pre-
vious workers, the formula of the red complex is established as CazZz (rather than CaZz) while that of the purpleblue complex is CazZ (rather than CaZ). The behavior of the indicator is summarized b y a pCa-pH diagram estabIished from the formation constants of the metal-indicator species. The conflict between the conclusions of this study and those of Close and West underscores the difficulty in interpreting such a n involved system from a partial study. Even the present study failed t o define completely all the complexes of calcium with AABSN. I n addition to CazZz and CazZ, at least one and possibly two other complexes exist under restricted conditions but were not characterized quantitatively in spite of considerable effort. EXPERIMENTAL
Purification of AABSN. llizarin Acid Black SN, suitable for uie as a metallochromic indicator, was obtained as the trisodium salt from Lamont Laboratories, 5002 K e d Mockingbird Lane, Dallas, T e s . T h e indicator is about 3570 pure, t h e major impurities being sodium salts used to salt out the indicator in manufacture. T h e indicator was purified for stability constant studies b y two precipitations from aqueous solution b y addition of HCl. The precipitated indicator was dried a t 80” C. under vacuum and stored in a 1 Present address, Chemstrand Research Center, Durham, N. C. 2 Present address, Department of Chemistry, Rensselaer Polytechnic Institute, Troy, N. Y.
