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, l a p a n
b A systematic study o f 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 o f 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 o f 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 b e 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 phosphate systems (8,9) have also been used 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.
EFFLUENT, ml
I
0.5M HCI
-
0
0
50
100 EFFLUENT, m I
05 M HCI-0.5 M NH&N-I-
I50
0.5M NaOH-0.5M NaCl
n
200
-
Figure 1 . Experimental elution curves for rhenium and molybdenum A. Rhenium eluted first with O.5M NH4SCN0.5M HCI, then molybdenum with 2.5M N H ~ N O B solution 8. Rhenium eluted nrst with 0.5M N H X N 0.5M HCI, then with 2.5M NH4N03 and 0.5M NaOH-O.5M N a C l solution C. Rhenium eluted first with 0.5M NHISCN0.5M HCl, then molybdenum with 0.5M NaOH0.5M N a C l solution only
resin was then converted to t h e thiocyanate form by passing 1 M KH4SCN solution through the column (500 ml. of 1X NH4SC?; solution per 50 ml. of swollen resin). After the column had been washed with deionized water, the resin was removed from the column and stored in a desiccator over a saturated potassium bromide sdution. ION EXCHANGE COLUMN. Three grams of dried resin was slurried with water and poured into a conventional ion exchange column, 1.0-cm. i d . , pulled to a tip, and plugged with glass wool at the outlet of the column. The resulting resin bed is usually about 6.5 cm. long. The eluent was introduced through a 100-ml. separatory funnel whose stem was attached to the top of the column with rubber tubing. SilocK SOLUTIONS. Rhenium. Appropriate amounts of ammonium perrhenate, prepared from 99.99% purity metallic rhenium, were dissolved in 0.5M HC1 and diluted to 50 ml. with the same acid to give about 2 mg. of Re per ml. The strength of the solution was standardized gravimetrically with tetraphenylarsonium chloride ( 5 ) . Molybdenum. Molybdenum trioxide (3.75 grams) was dissolved in 10 ml. of 1 to 1 S H 4 0 H , acidified with hydrochloric acid, and diluted to 50 ml. to give about 50 mg. of Mo per ml. of 0 . 1 X HCl. This solution was standardized gravimetrically with a-benzoinoxime (4). Further dilution was made, whenever needed, with 0.1X HC1 solution.
Technetium. Proper quantities of molybdenum trioxide were irradiated for 6 hours a t the power level of 100 kw. and neutron flux of 5 X 10" in the TRIGA I1 reactor of St. Paul's University, Tokyo. The Tcggm,daughter of 11099, was separated from molybdenum by extracting as tetraphenylarsonate into chloroform ( I S ) . Carrierfree Tc9gm was then back-extracted in 0.2M HC104. The radiochemical purity of Tcggmtracer (0.14 m.e.v., 6.04 hours) was checked against gamma spectrometry and half-life determination and proved to be completely free from foreign activities. Procedure. DETERMINATIONO F METAL IONS. Rhenium and molybdenum in effluents were determined spectrophotometrically with thiocyanate-stannous chloride (11) and dithiol ( I O ) , respectively. Activity of Tc99" was measured with a standard well-type scintillation counter. The gamma detector was a thallium-activated sodium iodide crystal 1 3 / 4 inches in diameter and 2 inches thick. Fractions taken from the column were counted in 10-ml. screw-cap polyethylene vials. EQUILIBRIUM STUDIES. The distribution coefficients, Kd, for rhenium and molybdenum as a function of c m centration of ammonium thiocyanate were determined by a batch method, keeping the concentration of hydrochloric acid constant at 0.5M. Onegram portions of dried resin were weighed and placed in conical flasks with glass stoppers to which 42-1111. portions of 0.5M HC1 solution containing varying amounts of ammonium thiocyanate and 1.41 mg. of rhenium or 0.96 mg. of molybdenum were added. After mechanical shaking for 20 hours at room temperature, two phases were separated by filtration. An aliquot of the filtrate was analyzed for the respective element colorimetrically. The Kd value was then estimated by the following formula:
Kd
=
concn. of ion in resin phase/gram of resin concn. of ion in solution phase/ml. of soln. COLUMN SEPARATION.Before use the resin bed should be washed thoroughly with 0.5M NH4SCN-0.5M HCl solution until the concentration of NHaSCh' in the effluent matches that in the eluent. Up to 8 ml. of the sample solution, 0.5144 in NH4SCN and 0.5M in HCl, is loaded on top of the column. When the sample solution reaches almost the top of the column bed, the elution is started with the solution, 0.5X in NH4SCN and 0.5M in HC1, a t a flow rate of 1 ml. per minute to desorb the rhenium. For complete elution of rhenium, 100 ml. of eluent is sufficient, regardless of the amounts of rhenium present. hlolybdenum is then eluted with 2.5M "4x03 solution. When large quantities of molybdenum ( > 5 mg.) are present, 0 . 5 X NaOH-0.5M NaCl solution is preferable as eluent to reduce the required volume of eluent.
Table I.
Run 1 2
3 4
5 6 7 8 9
Separation of Rhenium and Molybdenum
Taken, p g . Re Mo 48 14,700 190 980 970 4,900 29 4800 9,800 5800 39 19,600 39 19,600 150 19,600 150 19,600
Recovered, p g . Re h l o 48 14,100 180 930 970 4,600 4700 28 6000 9,300 40 19,400 42 17,700 140 17,800 150 19,500
Technetium remaining on the column after removal of rhenium can be eluted with 4M HKOs solution a t the same flow rate as that for rhenium elution. RESULTS AND DISCUSSION
K d values of rhenium as a function of ammonium thiocyanate concentration in 0.5.M HCl are: 319(0), 67(0.13), 48(0.25), 17(0.50), 66(1.0), and 79(2.0), where values in parentheses indicate the molar concentration of ammonium thiocyanate. Molybdenum is strongly adsorbed on the resin over the same concentration range as rhenium, indicating Kd values greater t'han lo4. This suggests that the separation of rhenium and molybdenum in this system is feasible. As the concentration of ammonium thiocyanate incrertses, Kd values of rhenium drop to a minimum of 17 a t 0.5M NH,SCN and then rise very slowly. The dip in the K d values might indicate that there are possibly two species of rhenium present a t the concentration range covered here. To reduce the time for rhenium elut,ion it would seem profitable to use the eluent system 0.5M in NH,SCN and 0.5X in HC1. T o determine an optimum elution condition for molybdenum, a number of experiments were carried out in a variety of eluent systems. Ammonium nitrate appeared to be advantageous because of the rather small volume of eluent required to complete the elution. Kd values of molybdenum for the thiocyanate form of Dowes 1-X8, 100- to 200-mesh, in the ammonium nitrate system were measured by a batch method. The following values were obtained as a function of ammonium nitrate concentration: 482 (0.05), 122(0.25), 38(1.0), and 0.3(5.0), where the values in parentheses indicat,e molar concentration of nitrate. hlthough 5.051 XH4N;O3 solution shows the lowest Kd value, its use results in no advantagrs, because too much nitrate causes trouble in further processing the effluent and makes the flow rate too slow. The 2.5.11 XH,S03 solution provides an excellent means to desorb from the column milligram VOL. 36, NO. 8, JULY 1964
1655
U
0
ul
(3) Fischer, S. A., Meloche, V. W., ANAL. CHEM.24, 1100 (1952). ( 4 ) Hillebrand, W. F., Lundell, G . E. F., “Applied Inorganic Analysis,” 2nd ed., p. 310, \Viley, Sew York, lY5!). (5) Ibzd , p . 320. (6) hleloche, V. VV.) Preuss, 4.F., ANAL. CHEM.26, 1911 (1954). ( 7 ) Pirs, M., hlagee, R. J., Talanta 8, 395 (1961). (8) IijT‘abchikov, I). J., Borisova, L. M., Zh. Anal. Khim. 13, 340 (1958).
A
I
I
-
0
Re
50
100
I50
200 EFFLUENT, m I.
250
300
350
450
400
Tc
I-‘
(1
TC (Tracer I
( 9 ) Ibid., p. 482.
(10) Sandell, E. B., “Colorimetric Determination of Traces of Metals,” 3rd ed., p. 650, Interscience, S e a York, 19.59, (11) Zbid., p. 754. ( 1 2 ) Sen Sarma, R. K.,rlnders, E., Miller, J. M . j J . Phys. Chem. 63, 559 (1959). ( 1 3 ) Tribalat, S., Beydon, J., Anal. Chim. d c t a 6 , 96 (1952).
8
g z o u d d
for review November 26, 1963. RECEIVED i2ccepted March 16, 1964.
00
50
IO0
I50
200
EFFLUENT
Figure 2.
250
,m I
300
350
400
450
Corrections
I
Experimental elution curves for 1 mg. of rhenium and tracer quantities
of technetium A. E. “03
Rhenium eluted first with 0.5M NHdSCN-O.5M HCI, then technetium with 0 . 5 M HClOa solution Rhenium eluted first with 0 . 5 M NHaSCN-O.5M HCI, then technetium with 2.5M NHaN03 and 4M solutions
quantities of strongly adsorbed molybdenum. Leqs than 100 ml. of eluent is usually sufficient to remove molybdenum from the column. However, the volume required for elution increases when the amount of molybdenum increases; approximately 320 ml. of 2.551 xH&03 solution is necessary to elute 5 mg. of molybdenum completely from the column. I n such cases the 0.5M SaOH-0.5-11 NaCl solution gives an excellent elution system. However, to elute large amounts of molybdenum, the colunm should be first washed with several column volumes of 2.5111 NHaNO3, and then an eluent of 0.551 KaOH-0.511 NaCl be used. Otherwise, residual amounts of molybdenum will remain on the resin, and yields will be low. Figures 1 and 2 illustrate the elution curves for molybdenum-rhenium mixtures. No positive test for molybdenum was ever found in rhenium fractions and vice versa. Results on the separation of rhenium and molybdenum are listed in Table I. In runs 7 and 8 molybdenum was eluted with a 0.5,11 NaOH-0.5M NaCl solution after removal of rhenium, without washing the column with 2.531 h H4N03 solution. The omission of the preliminary washing step with ammonium nitrate solution gives a slightly lower recovery for molybdenum (approsimately 9 0 ~ o ) . Rhenium is completely separated from tracer amounts of technetium by elution with 100 ml. of the 0.511 NH41656
ANALYTICAL CHEMISTRY
SCK-0,511 HC1 eluent, as is the case for the separation of rhenium and mclybdenum. No Tcg9“ activity was found in the eluted fractions of rhenium, nor were color reactions of rhenium observed in the technetium fractions. The eluticn curves of 1 mg. of rhenium and tracer quantities of technetium are illustrated in Figure 2, A and B. Recovery of rhenium is quantitative. Subsequent eluticn of technetium remaining on the column is conducted with 0.511 HC1O4or 4-11 HSO3 solutions. In bcth case; a rather prcnounced tailicg effect aj,l:em fer the elution of technetium. ’The technetium recoveries were 30% when eluting with 350 ml. of 0.5-11 HCIOl and 60% when eluting with 220 ml. of 4.0M H S 0 3 solution. Technetium recovery can be improved by slowing donn the eluent flow rate so that equilibrium can be almost attained. The present procedure for the separation of rhenium has some distinct advantages over many other anion exchange separation techniques. In most cases, a sharp band with very little tailing is obtained, regardless of the quantities of rhenium present. The thiocyanate-hydrochloric acid system will provide a greater possibility for the clear separation of rhenium from a number of elements belonging to the thiocyanate group. LITERATURE CITED
(1) Atteberry, R . W., Boyd, G. E., J . Am. Chem. SOC.72, 180.5 (1950). ( 2 ) Boyd, G . E., Larson, Q. V., J . Phys. Chem. 60, 707 (1956).
Spectrophotometric Determination of Iron in Ethylene Amines with Phenyl-2pyridyl Ketoxime I n the article by Robert Chemin and E. R. Simonsen [ . ~ N A L . CHEM. 36, 1093 (1964)] on page 1094 the title of Table I1 should read “Recovery Data in Triethylenetetramine and Tetraethylenepen tarnine.”
S pectro p hoto metric Microdetermination of Lebaycid, O,O-Dimethyl-O-[4-( methylthio) -m-tolyl] phosphorothioate In this article by Yoshio Hirano and Teiichi Tamura [ANAL.CHEM.36, 800 (1964)l two errors appeared in the reaction scheme on page 800, column 2. The reaction should be as follows:
N a O OS--CHS ‘CHis
