series of solutions prepared with a constant initial quantity of nickel(I1). This problem is illustrated in Table 11. which gives the ratio of the cathodic to anodic current coml)onents and the ratio of the total current to the concentration of argentocyanide ion for a concentration series with a tot,al nickel(I1) concentration of 4 X 10-3AlI. It is quite difficult to determine the act'ual correction for reeidual current. Hence, a nonlinear relationship of the total and anodic currents of the wave with the conrentration of argentocyanide ion is the rewlt. Care must be exercised in a1q)lication of this method to any concentration series extending to lobver li~vclsif the full analytical utility of t'he method is to be realized. An intere>ting extension of this metlioti is to the simultaneous polarogralihic dvtermination of silver and nier( v i ~ y . Sinw mercuric cyanide gives only a c*athodic*reduction wave, the anodic c~~riw of tthe wave obtained for a mixture of mercuric cyanide and argentoryanide ion would allon- the estimation
of the silver content, whereas the difference between the anodic and the ?athodic current values would represent the mercury. Even in thc light of thc limitations descrihed, thir alqdication should prove useful sinre relatively fen. method5 are extant for the simiiltancous measurement of thrw t\vo mrtals. It is apparent, from a consideration of the
cury. The method would not be useful if the reverse ratio of silver and mercury is present. Varioui; ratios of the two metals were analyzed simultaneously using this technique and the results are tabulated in Table 111. The constancy of the i(,,;r ratios for silver and mercury s h o w the technique to he pot,entially useful for this application. ACKNOWLEDGMENT
The authors are indelited to R . S. lliller for his assistance in (wrying out the radioisotopic experiments.
LITERATURE CITED
( 1 ) Bowers, 11. C., Kolthoff, I. J . ilm. C h m . Soc. 81, 1836 (1959). (2) Cave, G . L. B., Hume, 1). X., A~YAI,. CHEM.24, 58X (1952). ( 3 ) 1)aanall. R. 31.. \Vest, T. 6.. 7'alanta
( 4 ) 'Israel, Y.,'\'ronian, A , , A N A L .CHEM. 31, 1470 (1959). ( 5 ) Kernula, \V., Kublitz, Z., Anal. ('him. A c t U 18, 104 (1958). ( 6 ) Kolthoff, I. XI., Hurne, I ) . S . ,J . A m . ('hem. SOC.7 2 , 4423 (1950). ( i )Kolthofi', I. M., Lingane, J. J., "Polarography," 2nd ed., Vol. I, p. 208, Interscaienc.e, Sew York, 1052. ( 8 ) Kolthoff, I . M., hliller, C. S.,J . Am. ( ' h e m . Soc. 63, 1405 (1941). (9) lleites, I,., Meites, T., Ihid., 73, 395 (3951). (10) Sewman, L., Cabral, J . O., Hume, I). S . . Ihid.., 80.. 1814 (3958). (1 1) Tanaka, s.,hlurayanl'a, T., z. Physik. ('hem. (Frankfurt,) 11, 366
(1957).
(12) Tomes, J., ('ollection ('tech. Chem. ('ommms. 9 , 81 ( 1 9 3 i ) . (13) \Vest, P. I>ean. J. F., Breda, E.
J.,Ihid., 13, l(1948). RECEIVED for review January 13, 1964. Awepted April 20, 19G4. Ilivision of Analytical Chemistry, 147th Meeting, ACS, Philadelphia, Pa., .4pril 1984.
Argentometric Titration of Sulfide in Alkaline Solutions C. H. LIU Department o f Chemistry, Polytechnic lnstitufe o f Brooklyn, Brooklyn, N . Y . SAMUEL SHEN Department o f chemistry, Long Island University, Brooklyn, N. Y.
b Determinations of sulfide were performed b y argentometric titration with a potentiometric end point in strongly alkaline ammoniacal solutions. A rotating silver sulfide-silver indicator electrode was used in these titrations. Potential equilibrium was attained rapidly, and the potential break around the equivalence point was very large. Sulfide (0.2 to 4 mg.) in the concentration range 5 X l o p 4 - 1 X 10-*M could b e determined with relative errors of 2 to 4 parts per thousand. The simultaneous determination of sulfide and cyanide in this medium was feasible with two distinct potential breaks in the titration curve. The solubility product of AgpS and the dissociation constants of the complexes [ A g ( C N ) * ] - a n d [ A g ( N H & ] + evaluated from potentiometric measurements agreed well with literature values. The silver sulfide-silver system was thus shown to b e an adequate indicator electrode for argentometry. The effect of aging of the silver sulfide precipitate and the silver sulfide-silver electrode on the potential was also investigated and found to b e minor, causing no difficulties in the titration. 1652
ANALYTICAL CHEMISTRY
HILI.: argentometric titrimetry W i v i t h a potentiometric end point has been extensively investigated and widely applied in the determination of halide>, success has heen rather limited in extending this method to the anal of the sulfide ion ( I O , 1 4 , 1 5 ) . Kolt and Furman havc notrd that in a titration of hydrogen sulfidc~with silver nitrate, the end point is always premature liy as much as 1007, ( 9 ) . Formation of silver bisulfide or t,he occlusion of sulfid~interferes with the stoichiometry of t.he reaction. Tamele et a / . performed argentometric titration.; of bisulfide in a sodium acetatmemedium (fI, 1 2 ) . The exlierimental det'ails of the Iiotrntial measiiremcnts and tmhe behavior of the silver sulfide-silver indicator electrode were not report'ed. Indirect determinat,ion of sulfide by chelometric titrations, using ethylenenitrilotetraacetate, was described (4, 7 ) . The titrimet,ric determination of sulfide, however, i!: usually 1 i a - d upon oxidation-reduction reactions ( 5 , A', 13). Since thc composition of the silver sulfitlc preciilitate is uncertain at lo\ver ])€IJ>>it is advisahle t o perform the :ii,gentometric titrations in strongly
alkaline solutions. In these cases, however, coprec-ipit,at8ionof silver oxide is likely. Furth-rmore, the precipitation of the oxide in the vicinity of the equivalencc iioint hinde1,r the rapid attainment of equilibrium in the solution and delays potential measurement in the titration. The objcctives of the present work are to test the feasihility of the argentometric titration in a strongly alkaline solution in the presence of ammonia which solubilizes silver oxide, and to investigat'e the behavior of the silver sulfide-silver system as an indicator electrode. T h t simult'aneous determination of sulfide and cyanide is also >hewn to be possible because of the extremtly negativv potential of the silver sulfide-silver electrode. EXPERIMENTAL
Reagents. Standard sulfide solution. Hydrogen ulfide was generated by acidifying a qolution of analytical grade sodium sdfidc, passed through t w o scrul)hers of distilled water to r e m o v e thc small amount of contaminating sulfur dioxide, and absorbed in a n air-free 1.11 sodium hydroxide
'
01
1
ML OF 0 0 2 6 9 4 v ASNO,
Figur e
1.
Replicate titration
ml. of 0.00291OM a n d 1M NHI
30
curves
Na2S, 0.1M N a O H ,
solution. A flow of purified nitrogen was maintained prior to and during the generating process to remove oxygen and to aid in flushing the hydrogen sulfide produced into the absorbing solution. The alkaline sulfide solution obtained was stored under nitrogen in an automatic3 buret. Aliquot's of the solution were analyzed by the procedure of I3ethge ( 2 ) . The sulfide solution was added to a standard potassium iodat,e solution in 3.5 to 5.U sodium hydroxide, and the rwulting mixture was boiled for a few minutes to oxidize the sulfide to sulfate. After cooling, potassium iodide was added and the solution acidified under cooling by t'ap water to generate iodine. The iodine produced was then titrat,ed with a standard potassium thiosulfate solution to the starch end point. All other reagents used were analytical grade chemicals. Apparatus. Indicator and reference electrodes. A rotating platinum electrode (E. H. Sargent Co., Chicago, Ill.) was plated with silver from a silver cyanide b a t h and anodized lightly in a n alkaline wlfide solution. T h e silver sulfide-silver electrode thus prepared was used as the indicator electrode. Freshly prepared elect,rodes were used in this work although they still functioned well after being kept in an air-free alkaline sodium sulfide solution for two weeks. I n some cases, a iilver wire freshly anodized in an alkaline sulfide solution was used. .A Ikvkman saturated calomel electrodr was used as the reference elect rod e. Pot en t ionieter. ai Rubicon portable potentiometer was usrd. Procedure. Solutions of ammonia and sndiuin hydroxide were placed in the titration beakw and standard siilficlc solution wa. added so that' the final solution wa.: about 0.1 .II in sodium tiydi,oxirlr~,1.11 in ammonia, and 5 X 10-4 - 1 x 10-2.11 in sulfide. The total volumc TKLS 25 t o 100 ml. The solkition ivab prntwted from atmospheric c)sypcn b y a stream of nitrogen over the
surface. The indicator and reference electrodes were placed in t,he solution which was stirred by a magnetic stirring bar. The solution was then titrated potentiometrically with standard 0.010.05.11 silver nitrate. The potential was measured 1 to 2 minutes after each addition of silver nitrate prior to the equivalence point. The electrode potential attained the equilibrium value more quickly when the indicator electrode was rotated mechanically. Furthermore, without the mechanical st,irring, the precipitated silver sulfide tended to gather on the electrode surface. Some solution would be immobilized around the electrode, makinq its response more sluggish. Without the mechanical rotation, manual shaking of the electrode was necessary from time to time. After the equivalence point, potential equilibrium after each addition of silver nitrate was attained practically instantaneously. The titration curve was then analyzed by conventional method to determine the end point. RESULTS AND DISCUSSION
In t,he concentration range of 5 x lop4 - 1 X 10-2M sulfide, the titration curve was well defined. The potential break at the end point was very large, presenting no difficulty for its location. Figure 1 presenh two replicate titration curves. Sodium hydroxide concentrations greater than O.l.lP did not show any advantage, and the ammonia concentration was kept at' 1Jd t'o ensure the absence of local formation of silver oxide. Typical analytical results are given in Table I. The relative standard deviations for series of five replicate determinations are about 0.4%. At concentrations less than 1 x 10F4X,the shape of t'he titration curve became somewhat irregular. Althoxgh it was still possible to detect the end point, t,he relative error is considerably larger. The method was then tested for possible interference by other anions. I t was found that chloride, sulfate, and sulfite did not interfere with the determination, and essentially the same precision and accuracy were obtained. The effect of aging of the sulfide precipitate on the potential was t'hen investigated. Measured amounts of silver nit,rate were added to standard solut'ions of sulfide in the titration medium, and the potential a t t'he silver sulfide-silver electrode was measured as a function of t'ime. A stable equilibrium value was reached in each case after 40 minutes, and the total potential change during this period was 0.0060.008 volt in the negative direction, representing a 25 to 35y0 decrease in the solubility of silver sulfide. The color of the precipitate also changed from brown to black. Thus, the potent,ial readings in the course of a titration, which were taken 1 to 2 minutes after
,
0 1
,
I
,
I
,
~,
I
,
OO-
-
-02-
-
-0.4
-
-
l
,
l
urements in the experiments on t,he effect of aging of the silver sulfide precipitates, and the
Table I.
Results of Sulfide Analyses
Sulfide by iodate method, mg. ( 2 ) 3 780 2 740 1 830 1 652
0 3780
Sulfide hy argentometry, mg. 3 785 2 746 1
837
1 657 0 3788
VOL. 36, N O . 8, JULY 1964
1653
value of K z for hydrogen sulfide, 1 x 10-14, given by Bower and Bates ( 3 ) , the pK., of silver sulfide was calculat,ed t,o be 48.8 compared to a previously report,ed value of 49.2 (6). From the titration curves, the pKd’s of the silver complexes of cyanide, [-lg(CS)2]-, and ammonia, [-1g(NH&]+, were evaluated to be 20.7 and 7.1, compared to literature values of 21.1 and 7.0, respect,ively (1). Concentrations were used in the calculations, and the ionic strength was essentially 0.1 in all cases. In view of the complicat’ed system under consideration, the agreement was quite satisfactory. The silver sulfide-silver electrode thus showed reversible behavior in the titration medium and served as an adequat’e indicator electrode for argentometry. I t should be pointed out in conclusion that in addition to t’he sensitivity, anot’her
important advantage of this method is that reducing species such as sulfite, sulfur, and thiocyanate do not interfere with the titration as they do in methods based upon oxidation-reduction reactions.
Meites, ed., McGraw-Hill, Xew York, 1963. (7) Kivalo, P., ANAL.CHEM.27, 1809 (1955). (8) Kolthoff, I. AT., 2. Anal. Chem. 60, 450 (1921). 19) Kolthoff. I. A I . . Furman. S . H.. “Potentionic&ic Titrations,” 2nd ed., kiley, S e w York, 1931. (10) Koltlioff, I. hl., Verzijl, E. J., Rec. Trac. (‘hzm. 42, 1055 (1923). (11) Taniele, hl. LV.j Irving, V, C., Rvland. L. B.. AML. CHEY.32. 1002 (1360). (12) Tamele, 11. W.,Ryland, L. McCoy, R. S . ,Ibzd., 32, 1007 (1961 (13) Treadwell, F. P., ,,Hall, W. ~
LITERATURE CITED
(1) Aikens, D. A,, Reilley, C. N., 1-37 in “Handbook of Analytical Chemistry,” L. Meites, ed., McGraw-Hill, New York, 1963. (2) Bethge, P. O., Anal. Chim. ilcta 10, 310 (1954). ( 3 ) Bower, V. E., Bates, R G , 1-20 in “Handbook of Analytical Chemistry,” L. Meites, ed., McGraw-Hill, New York, 1963. (4) BudCSinskj., B., VaniEkovB, E., Korbl, J., Coll. Czech. Chem. Commun. 2 5 , 456 (1960). (5) Charlot, G., Bull. SOC.Chim. France ( S e r . 5) 6, 1447 (1939). (6) Frankenthal> R. P.,1-13 in “Hand-
book of Analytical Chemistry,” L.
“Analytical Chemistry, Vol. 11, p . 9th ed., Riley, Sew York, 1 w . Y (14) Treadwell. W. D.. W’ei
Chim. Acta 2 , 680 (1919). (15) Willard, H. H., Fenwick, F., J . A m . L‘hem. Sot. 45, 645 (1923).
RECEIVED for review January 6 , 1964, Accepted April 15, 1964. lliv ision of Analytical Chemistry, 145th Meeting ACS, Sew York, S . Y., September 1963.
Anion Exchange Separation of Rhenium from Molybdenum and Technetium in ThiocyanateChloride Media HlROSHl HAMAGUCHI, KAZUAKI KAWABUCHI,’ and ROKURO KURODA Department o f Chemistry, Tokyo Kyoiku University, Koishikawa, Tokyo, lapan
b A systematic study of the adsorption of Re(VII) with a strongly basic anion exchanger, Dowex 1-X8, in NH,SCN-HCI medium indicates that the difference in the equilibrium distribution coefficients of Re(VII) and either Mo(VI) or Tc(VII) i s large enough for sharp separation. An anion exchange chromatographic procedure was developed for the separation of Re(VII) from Mo(VI) or Tc(VII). Re (VII) i s first eluted with 0.5M NH,SCN0.5M HCI solution while Mo(VI) or Tc(VII) remains adsorbed strongly on the column. Mo(VI) i s then removed quantitatively b y passing 2.5M “,NO3 solution through the column. A 0.5M NaOH-O.5M NaCl solution i s preferable to “,NO3 when large amounts of Mo(VI) are present. Tc(VII) i s eluted with 4 M “ 0 3 solution, which gives a Tc(VII) recovery of about 6OY0. Microgram to a few milligram quantities of Re(VII) can be quantitatively separated from Mo(VI) in proportions of Re:Mo = 1 :500 to 170: 1 and from tracer quantities of Tc(VII).
T
separation of rhenium from molybdenum and technetium has been a difficult and tedious operation in analytical and radiochemistry. Fischer and lleloche (3) have separated HE
1654
ANALYTICAL CHEMISTRY
rhenium from molybdenum by passing a 10% S a O H solution of perrhenate and molybdate through a basic anion exchange column. Molybdenum is recovered in the effluent, while rhenium is retained on the resin and then recovered by elution with 7 to 8-11 HC1 solution. Meloche and Preuss (6) have recommended potassium oxalate for the separation and elution of molybdate and perchloric acid for the subsequent elution of the perrhenate. Anion exchange reactions in phoshave also been used phate systems (8,9) to separate rhenium from molybdenum. The ion exchange of technetium and rhenium was first studied by htteberry and Boyd ( I ) , using Dowex 2 ion exchange resin in the sulfate form and separating perrhenate from pertechnetate with a 0.1.11 XH4 SCS-(NH4)2 SO4 solution a t pH 8.3 to 8.5. Perrhenate has also been separated from pertechnetate by elution from Dowex 1 and 2 with 0.231 HC1O4 (12) or 0.25.11 HClO, ( 2 ) , respectively. These procedures did not clearly separate rhenium and techr netium. Recently, Pirs and Rlagee ( 7 ) have provided a promising procedure for the anion exchange separation of technetium, rhenium, and manganese. Permanganate is first reduced chemically so that it is not taken up by the anion exchanger. After the manganese
has been washed down, perrhenate is eluted with 0.2M NH,SCS in 0.1111 HCI a t a flow rate of 1 ml. per 15 minutes, and then pertechnetate by 451 HSO, solution a t the same flow rate. A short column provides good separation; however, about 5 hours are required to remove rhenium from the column. The thiocyanate-hydrochloric acid medium coupled with a base-type anion exchanger appeared to warrant more extensive investigation. A systematic equilibrium study showed that the distribution coefficient of rhenium differed enough from those of molybdenum and technetium to ensure good separations. Separation of rhenium from other element. of the thiocyanate group should also be sharp. EXPERIMENTAL
Apparatus and Reagents. IONExCHANGE RESIK. Strong base-type anion exchanger, Dowex 1-X8, thiocyanate form, 100- to 200-mesh. Before use the resin was put into a large column and washed with 1M HCl solution and then with deionized water until the chloride test with silver nitrate was negative. T h e 1 Present address, Chemistry Labarat,ory, Ehinie University, Matsuyania, Japan.
