partment of the Essex County Council for supplying the monies necessary for carrying out this progr:Lm. LITERATURE CITED
( 1 ) Anthony, P., Zeitlin, H., lVature 187, 936 (1960). (2) Ballhausen, C. J., “Introduction to Ligand Field Theory,’ p. 171, McGrawHill, New York, 1962. (3) Brehler, B., Z. Krist 109,68 (1957). ( 4 ) Delwaulle, M., Bull. SOC. Chim. France 1955, 1294. (5) Evans, R. C., Mann, F. G., Peiser, M. S., Purdie. D., J . Chem. SOC.1940. 1209. ( 6 ) Fromherz, H., Lih, K., 2. physik. Chem. (Leipzig)A 167, 103 (1933). ( 7 ) Goya, H., Waugh, J. L. T., Zeitlin, € I . . J . Phus. Chern. 66, 1206 (1962). 18) Griffiths. T. R..’ Ph.D. thesis. ’ Southampton University, England, 1960: (9) Griffiths, T. R., Colchester, England, unpublished results, 1962. (10) Griffiths, T. R., Lott, K. A. K., Svmons. M. C. K., ANAL.CHEM.31,1338 (i959). ‘
(11) Griffiths, T. R., Symons, M. C. R., (26) Naughton, J. J., Frodyma, M. M.: Trans. Faraday SOC.5 6 , 1752. Zeitlin, H., Science 125, 121 (1957). (12) Jahoda, F. C., Phys. Rev. 107, 1261 (37) Rolfe, J. A., Sheppard, D. E., (1957). Woodward, L. A., Trans. Faraday Soc. J . Chem. (13) Janz, G. J., James, 11. W., 50, 1275 (1964). Phys. 38,905 (1963). (28) Smith, PIT., Ph.D. thesis, Southamp(14) Kortuni, G., Spectrochim. Acta Suppl. ton University, England, 1958. 1957, 534. (29) Symons, M. C. R., Trevalion, P., (15) Kortum, G., Trans. Faraday SOC. Spectrocision 10, 8 (1961). 58, 1624 (1962). (30) IYells, A . F., “St,ructural Inorganic (16) Kortum, G., Braun, W.,2. physik. Chemistrj-,” p. 345, Oxford University Chem. (Frankjurt) 18,242 (1958). Preps, London, 1062. 117) Kortum. G.. Kortum-Seiler.’ VI.. (31) We:idlandt8, IT-. IT., Franke, P. H., ‘ Z. Naturfo;sch. Za, 652 (1947). Sm:t,h, J . l’,> BNAL.CHEM. 35, 105 (18) Kortum, G., Schlotter, H., Z. Elek(1063). trochem. 57, 353 (1953). ( 3 2 ) Wolfsberg, &I., Helmholtz, I,., J . (19) Kortum, G., Vogel, +J., Z. physik. Cherii. P h w . 20, 837 (1952). Chem. (Frankfurt)18, 110 (1958). (20) Zbid:, p. 230. (33) Woodward, I,. .I.,Quart. Bev. 10, f21) Kortum. G.. Vouel. J.. Braun., W.. 185 (1956). , Angew. Chem. 7 0 , 6gl (1058). 1341 Zeitlin., 11.., CTOV:~. .Yature 183. I / H.. , (22) Kubelka, P., hfnnk, F., Z . tech. 1041 (1959). Physzlc 12, 513 (1931); J . O p t . Soc. 135) Zeitlin. H.. Siimot>o. A.. . ~ s A I , . Am. 38,448 (1948). (23) Lermond. C. A . Itoeers.’ L. B.. ‘ ANAL.C H E27,340 ~ (195a. 616 (l95g). (24) Liehr, A. D., J . Chem. Educ. 39, 135 (1962). RECEIVEDfor review hI:trch 1, 1963. (25) MacGillavry, C. H., Bijvoet, J. &I., a\ccepted May 2, 1963. 2. Krist. 94,249 (1936). ~
j
,
I
Anion Exc:hange Separation of Magnesium and Calcium with Alcohol-Nitric Acid JAMES S. FRITZ and HlROHlKO WAKl Institute for Atomic Research and Department of Chemistry, Iowa State University, Ames, Iowa
b Magnesium and ccilcium are separated b y anion exchange, using dilute nitric acid in a medium containing a high proportion of (1 water-miscible alcohol. A ”column separation factor” i s proposed and used in selecting the best eluting medium. A solution of 0.5M nitric acid in 90% isopropyl alcohol is the eluent. Amberlyst XN1002 resin is recommended for the separation.
A
of papers hake been published on the ,on exchange separation of magnesium and calcium. This separation has been done on a cation exchange resin merely by eluting with hydrogen ions ( I , l o ) , although the difference in affinity for the resin is not very large. To enhance the separability, compie\-forming agents such as ammonium ac:tate (6), ammonium formate ( I S ) , and ethylene (dinitrilo) tetraacetic acid (EDTA) (14) under proper pH conditions, have been used. An anion exchange separation was also made ( 11 ) . All of these c o m p l e h g agents used in Mg-Ca separation are salts of organic acids. Common inorganic acids spem more convenient ata the eluents, because the treatment and analysis of the effluent containing the metal after NUMBER
elution are easier in most cases. I n anion exchange which depends only on complexabilitp of a metal, however, alkaline earth metals have always been classified in a nonsorbable group, because neither element forms any complex anions in these aqueous acids or even in the resin phase. On the other hand, the addition of a water-miscible organic solvent to a metal-complex system makes the complex formation more effective. This sometimes leads to larger separability of metals in anion exchange (2-4, 7 , 8, 12, 15) as well as in cation eschange (5). Recently the Ca-Sr-Ba anion exchange separation, which is impossible using aqueous nitric acid, was done by Fritz and Garralda ( 3 ) using an isopro1)yl alcoholnitric acid mixture. I n the \‘resent work, an anion cxchange separation of magnesium and calcium is studied under various conditions using dilute nitiic acid in aqueousalcohol media. The best separation is accompliahed using 0 5.ll uitriv acid -90% isopropyl ale jhol. EXPERIMENTAI
Thfx anion elchange resin Amberlyst XS-1002 (Rohiii (9: IIaai Co.) w i b gioiind irito stnallc~rp:iiticale sizes; 40 t o 60 1ne.h W L ~ iiwd for bath expcrimeiiti and GO to 100 iiietah Resins.
for column experiments. The resin was converted t o t h e nitrate form with nitric acid. Csed resin was regenerated by washing t h e sorbed metals with extremely dilute nitric acid or pure water. Kitrate resin was stored in a dark place. Dowex 1-X8, 100 to 200 mesh, anion exchange resin was also used in nitrate form for comparison. -4lthough resins for batch experiments were roughly air-dried under suction, complete dryness was not attained. Reagents. Nitric acid, alcohols, EDTA, and other reagents were all reagent grade a n d were used without purification. Stock solutions of calcium, magnesium, nickel, manganese, aluminum, iron, zinc, cobalt, copper, and cadmium were prepared by dissolving their nitrates in pure mater or dilute nitric acid. Impurities in these reagents were generally negligible. Solut’ionsof magnesium, calcium, nickel, manganese, aluminum, and iron were sometimes purified by the ion exchange method or a small correction was made from a blank when i t was necessary in the recovery experiments. M i x e d Solutions. ‘llie e1ut:nt for tlic segarat’ion of magnesium arid calcium is prepared by mixing 100 nil. of 5 M nitric acid and 900 ml. of isopropyl alcohol in a 1-liter volumetric flask and diluting the solution to 1-olume with water. The sample soliitioii :ttltleci t o tlic coluirin is usiidly 10 nil. of the s:tnie solvent cotiiposition :LO t h e clucnt. ‘I‘hc metal VOL. 35, NO. a, JULY 1963
1079
0
120
60 TIME
Figure 1 . [MI t . [MI
A.
-.
6. C.
D. E.
I80
MIN.
Sorption rate measurement:
Sorbed omount of metal a i time f Sorbed amount of metal at equilibrium 0.25 mmole Mg, swollen Amberlyst XN-1002, ferf-butyl alcohol 0.25 mmole Ca, air-dried Amberlyst X N - I 002, isopropyl olcohol 0.25 mmole Co, swollen Amberlyst XN-I 002, terf-butyl olcohol 0.5 mmole Ca, oir-dried Amberlys: X N - I 0 0 2 , terf-butyl olcohol 0.25 mmole Co, air-dried Dowex 1 -X8, fert-butyl alcohol
50
60
70 ISOPROPYL
solutions used for batch experiments arc prepared in the same manner. Determination of Metal Ions. For t h e determination of all elements, standard E D T A titration methods are used. The concentration of E D T A titrant is 0.001 t o 0.05M, depending o n t h e amount of metal ion titrated. Details of titration procedure are described below. Sorption Rate Measurement. T o 1 gram of air-dried resin p u t in each stoppered glass vessel, 0.5M nitric acid-90% alcohol (tert-butyl alcohol or isopropyl alcohol) solution containing 0.25 or 0.5 mmole of metal ( J l g or Ca) is added and shaken mechanically. iifter a definite time ( 2 t o 180 minutes), a n aliquot of the solution phase is withdrawn and analyzed titrimetrically with EDTA. The sorbed amount of metal is calculated from the difference between total metal taken and the amount remaining in the solution phase. Some experiments were done with resin which was immersed in the same acid-alcohol mixture for about 30 minutes before addition of the metal. Distribution Coefficient Measurement in Various Alcohol-Nitric Acid Media. Twenty milliliters of 0.1 to 0 . 5 M H S 0 3 containing 50 t o 90% alcohol and 0.25 mmole of each metal ion is added t o 1 gram of resin. After shaking for 3 hours a n aliquot of solution is taken and analyzed. -411 equilibrations are done a t 24' + 1' C. The distribution coefficient, D,, is calculated as follows:
=
mmole of metal ion per milliequivalent of resin z o i metal ion per milliliter of solution
I n order to know the exchange capacity of resin taken, another 0.6 gram is transferred into a small glass column
at the time the resin is weighed for the batch process. The resin in the column is converted to the chloride form, and the exchange capacity is determined by 1080
ANALYTICAL CHEMISTRY
80
90
100
ALCOHOL %
Figure 2. Variation of De with nitric acid and isopropyl alcohol contents release of chloride ions with sodium nitrate, followed by Mohr's titration. For small G, values of magnesium, the calculation by column technique is applied as follows:
whcre
D, = volume distribution co-
efficient conversion factor between ml. and meq. Timsx = effluent volume, ml., at maximum concentration of eluted metal i = interstitial volume of column, ml. c = column exchange capacity
f
=
Loading Experiment. Conditions for batch equilibration are almost t h e same as above, except t h a t t h e metal amount is varied and 2 grams of resin is used for low loads of magnesium. I n making elution curves for column separations using various loads of magnesium and calcium, the sample solution is added to the Amberlyst column, and the elution with the same eluent is continued until a maximum concentration of calcium in the effluent is obtained. Five-milliliter fractions of the effluent are collected and analyzed for magnesium or calcium. Details of the column procedure are almost the same as described below. Procedure for Separation and Determination. A 10-ml. column (i.d. 1.1 to 1.2 cm.) is carefully prepared and 40 1111. of the fresh eluent s d it. The occurrence is ~ ~ t t through of bitbblrb in the re411 bed is avoided. A 10-inl. sample solution which contains no more t h a n 0.25 mrnole of calcium mid is 0.5M in nitric acid isopropyl alcohol is and 90% (IT./.)
added to the column. Collection of effluent from the column in a graduated cylinder is begun. The sample solution is passed through the column at a flow rate of about 0.3 ml. per minute. When no liquid is left above the resin bed, 1 ml. of eluent is added to wash the inside wall. Then the elution is carried out continuously by dropwise addition of 0.5M nitric acid-90% isopropyl alcohol from a separatory funnel. The flow rate is maintained at 0.5 to 0.6 ml. per minute. The first effluent equivalent to the interstitial volume is discarded, since it contains no metal ions. The next 40 ml. of effluent is taken for the Mg determination. A few 5-ml. fractions may be checked to confirm quantitative elution of magnesium. Then the eluent is changed and calcium is stripped with 30 to 40 ml. of 0.0254 aqueous HNOa a t a flow rate of -2 ml. per minute. Determination. The effluent for magnesium is diluted t o 200 t o 300 ml. and titrated with 0.05M E D T A , using Eriochrome Black T indicator after adjusting t h e p H t o 10 with ammonia, or a n aliquot of t h e effluent is taken and titrated with more dilute E D T A . If t h e amount of magnesium is small (less t h a n 0.05 mmole), magnesium is titrated with 0.01M EDTA, after t h e excess nitric acid and alcohol have been evaporated off carefully. Or preferably, the following technique is used for small amounts of magnesium. The effluent is made p H 7 to 8 with ammonium and passed through a 5-ml. column of the ammonium form cation exchanger Doivex 50W-X8. The column is washed with a small amouiit of water and msgiic+iuni is btripped with 10 nil. of ~~H-buft'eied solution containing a known amount of EDTA. After the column is washed with water, the e w e s EDTA is back-titrated with dilute ZnCll solution.
The calcium fraction is adjusted to pH 10 with ammoiiia and standard EDTA solution is added in excess. The excess EDTA is back-titrated with zinc chloride, using Eriochrome Black T indicator. RESULTS AND 1)ISCUSSION
Sorption Rate. The sorption rate for magnesium and calcium was compared using Amberlyst XS-1002 and Dowc.; 1-X8 resins. tert-Butyl alcohol was chosen to determine the equilibration time for the measurement of distribution coefficients because i t is the most viscous of the :ilcohols used. The amount of metal ion sorbed is plotted against equilibration time in Figlre 1. With the Amberlyst resin, calcium attains equilibrium in tertbutyl alcohol in about 2 hours. The rate of sorption is somewhat faster in isopropyl alcohol. The shape of the sorptior curve seems not to depend on the amount of metal ion taken or on whether the resin was preswollen in the nitric acid-alcohol mixture. I n the cace of magnesium, equilibrium is reached in a very short time in tert-butyl alcohol. On the other hand, 3 hours is still not sufficient for equilibration usi,ig Dowex 1-X8, despite the fact thal this resin is of smaller particle size than Amberlyst XS-1002 resin. 1f7e therefore conclude that Amberlyst XK-1002 is better for anion exchange separations in nonaqueous medium. Distribution Coefficients in Various Media. Three impoitant factors may be varied in seeking the optimum condition for the ion exchange separation of magnesium and calcium in nitric acid-alcohol s) stems: the kind of alcohol present, t i e percentage of alcohol. and the concentration of nitric acid used. First, a series of alcohols from methanol to tert-arr yl alcohol mas studied using 0.5-11 nitric acid containing 90To alcohol. Hie her alcohols were not used because of their immiscibility
Table I.
with aqueous nitric acid. Distribution coefficients are shown in Table I. The change of D,value with the variation of alcohol has almost the same tendency with both elements and both resins. However, the D. of calcium and magnesium with Dowex 1-X8 is always higher than with Amberlyst. -4mong the lower alcohols D, increases with decreasing dielectric constant of solvent, but among C4 or higher alcohols this becomes irregular. The solubility of organic solvents in water seems also to be related t o the sorbability of metal ion. .Ilthough many factors should affect a nonaqueous metal-anion exchange process, knowledge of the complex form of the metal ion and of the solvent composition in the resin phase might help to explain this behavior. The ratio of distribution coefficients is often called the “separation factor.” From this, methanol or ethanol may be chosen as the best solvent for separation. However, a separation factor should be a measure of the ability for column separation, because a separation by a batch technique is generally impossible. Therefore, the separation factor must be as follows :
s-
Vrnax(Y2)
VmaX(M1)
where TlmSx(~) indicates the effluent volumes from the beginning of the sample addition to the maximum concentration of metals pVIl and M2 in the effluent. When the D value is large and constant for each metal,
However, a t low D values the interstitial volume of the resin bed cannot be neglected. I n this case S becomes
4- z s = D”(M2) D~(.MI) +i or
s = D‘CUZ) f DS(.m) +
i, 2.
Results from Batch Experiments Using Various Alcohols
Dowex 1-X8 llcohol HzO
Methyl Ethyl n-Propyl Isopropyl n-Butyl Isobutyl
sec-Butyl tert-Butyl
Dielectric constantG 80 32.6 24.3 20.1 18.3 17.1 17.7 15.8 10,9”o 5.8
tert-*4rnyl a At 25” C. At 20’ C.
Solubility in waterb 0:
Amberlyst XN-1002
D*(Mk?)
Dc(~a)
N O
-0
De(~g)/
c3
7.9
c.
0.3
5.3
1.7
13.6
7.8
5.8
34
5.9
3.0
17.2
5.7
18
12.5 m
12.5
DdYd
-0
m
9 , 513“
Ds(coj/-
Dc(Caj-
02
c
where D, = volume distribution coefficient D2 > D1,i = column interstitial volume fraction, i, = column interstitial volume, ml. per resin meq. The separation factor is not constant and may change as each D value changes with the loading. I n Table I S values were calculated for the separation of calcium and magnesium. The value of i, = 0.32, which was used in the calculation, was considered to be a fairly constant value under the column separation conditions. Using S, separability was in the order: isopropyl alcohol > ethyl alcohol > n-propyl alcohol > tert-butyl alcohol. Any of these four solvents may be effective for magnesium-calcium separations when 0.5.1.1 nitric acid is used. However, the isopropyl alcohol-aqueous nitric acid system using Amberlyst XS1002 was chosen for further studies. A few experiments were done in which the nitric acid concentration or the organic solvent content was varied (Figure 2). The distribution coefficient of both elements increases with increased acid concentration and an increasing alcohol content. A nitric acid or isopropyl alcohol content higher than 0.5M nitric acid-90yo isopropyl alcohol seemed more effective theoretically for Mg-Ca separation. However, a high nitric acid content tends to react with organic solvent. The combination of a lower nitric acid content and a higher organic content results in poor solubility of metal ions, and the distribution coefficients change inconveniently with small changes in composition of the solvent system. For these reasons, 0.5M nitric acid containing 90% isopropyl alcohol was selected. Effect of Loading on Distribution Coefficient and Elution Curves. The distribution coefficient of a metal ion changes with loading. Therefore the elution position from a column depends on the amount of metal taken. For separations on a macro scale, it is necessary to know the relation between the sample load and distribution coeffi-
0.05d 0.21d 0.71 0.71 1.2 4.8 1.6 1.1 2.0
De(ca) -0 0.8 4.0 7.0 8.8 6.0 12.7 10.7 9.0 10.2
D6(Mg)
S(Ca,MIpf
-1 16 19 10 12 5.0 2.7 6.7 8.4 5.1
3 8.1 7.2 8.9 1.2
2.2 3.i 6.7 4 . .i
+
Separation factor calculated from S = D*(cs) 0.32 D ~ ( M ~0.32’ ) 5 Data from column technique.
c
+
VOL 35, NO. 8, JULY 1963
1081
10.0
-
Table 111. Distribution Coefficients of Other Metals in 0.5M "08-9OQ/o Isopropyl Alcohol
"----O
--b.
D.
Metal (Ca) Cd
5.0 L
(8.8)
3.2 2.0 1. 4 1.2 0.9 (0.71) 0.6 0.2
cu Co
~
0
n
A1
i
4
05t I
,
I
0.001
0.0005
Figure 3.
I
I
1
1
I
0.005 0.01 OD2 0.05 ai METAL LOAD, MlLLlMOCE METALIMILLIEPUIWPILENT RESIN
0.002
column. The elution curves from the 10-ml. and the 20-ml. column were almost identical in shape. Thus, if the elution is carried out so that the number of theoretical plates of the column is not varied, an extension to larger amounts
O'.
O3
Variation of distribution coefficients with load A. B.
Ca, batch experiment Mg, batch experiment
cient or the elution behavior. As can be seen in Figure 3, D, of calcium depends considerably on its load, ahile De of magnesium is less affected. This means that magnesium elution shows no long tailing and a beautiful separation may be expected. In Figure 4, elution curves using various amounts of metal ions are shown. Magnesium is quantitatively eluted within 4.5 column volumes in every case where the initial sample solution is 1 column volume or less. The elution position of calcium is af-
fected only by the amount of calcium, but not by the amount of magnesium. The calcium limit for a good separation seems to be about 0.25 mmole when a 10-ml. column is used. However, more calcium can be handled in a larger column. A quantitative separation of 0.5 mmole of calcium from 0.5 mmole of magnesium was accomplished within the same time as before using a column having the same length but twice t h e bed volume (20 ml. instead of 10 ml.). The volume flow rate from the 20-ml. column p a s twice that of the smaller
2 2
I-
Table 11.
Quantitative Separations of Calcium from Magnesium and Other Metals
Collected Metal Mg
Ca Mg
Ca
llg Ca
11g Ca Mg Ca
1fg Ca
lfg Ca
2 Ca Mg
Ca
+ Mn
Mg( Al, Fe)
Ca
1082
Taken, mmole 0 1765 0 2027 0 0392 0 0389 0 411 0 0389 0 371 0 0374 0 741 0 0374
Found,
0 0 0 0
0264 2478 0264 2478
0 0266 0 2487 0 0264 0 2487
0 1231 0 1035 0 0761 0.436 0.0950 0.2520 0.1052
0 1234 0 1038 0 0762 0,436 0.0948 0.2522 0.1054
mmole 1770 2020 0392 0389
0 0 0 0 0 0 0 0 0 0
111 0390 370 0374 742 0375
ANALYTICAL CHEMISTRY
effluent
yo error
+o
-0 0 0 -0
+o -0 0
$0
+o
3 3 0 0 7 3 2 0 1 3
+O 8 +o 3 0 0 +o 4 +o 2 +o 3
+o
fraction, ml. 45 5.5
55
Xotes
Flow 0 8 N 1 ml./ min. Sample volume 15 ml.
2
6
8
1
0
2
4
(COLUVI'N V~LJMEUNT)
55 45
47 42
Flow 0 7 N 0 8 ml./ min. Sample volume 15 ml Flow 0 5 0 il min
-
Figure 4. Elution various loads
curves
with
Column Flow Sample dimension, rate, Metal, vol., rq. cm. X ml./ Curve mmole ml. crn. min. A M g = 0.05 Ca = o.05 1 1.03 X 9.7 -0.5 Mg Ca Mg Ca
60
1
0.0 -0.2 +0.1 +0.2
4
EFFLUENT VOLdVE
60
D
45
E F
= 0.05 10 = 0.05
= 0.5 = 0.05
1.03 X 9.7 ~ 0 . 5
10 1.03 X 9.7 -0.5
~ ~ ~ o10 ~1.03o X: 9.7
t: Ff 109;"
=0.5
10 1.03 X 9.7 ~ 0 . 5
20 2.14 X 9.5 z 1 . 0
The separation data for foreign ions
in various combinations with calcium ALCOHOL
1
I
I
Ca
and magnesium are also given in Table 11. Calcium was quantitatively separated from nickel and manganese, and the separation and determination of magnesium and calcium were successful in the presence of nickel, iron, and
aluminum. LITERATURE CITED
0
EFFLUENT VOLUME, ml-
Figure 5.
Typical elution curves
Column (1.03 rq. cm. X 9.7 cm.) 10 ml. Mg, Ca = each 0.05 rnrnole
of calcium will be possible without taking any longer time, provided that the resin bed is carefully prepared. I n practice it is convenient to collect magnesium in one frwtion of effluent. Magnesium is usually eluted quantitatively (>99.9%) in 4,j ml. of the first eluent. and there is a significant volume of no metal flow before a breakthrough of calcium occurs. ‘Therefore if the separation is carried out under the same conditions as in the loading experiments. testing of the intervening effluent is unnecessary. X typical separation curve is shown in Figure 5. Testing will be desired for changed conditions of elution or for a sample of extremely different Ca-Mg ratio. Table I1 presents quantitative analytical data for various amounts and
ratios of calcium and magnesium. The results were satisfactory even under varying conditions such as a n increased flow rate and a n increased volume of initial sample solution. Distribution coefficients of other metal ions were measured by the same batch condition as for calcium and magnesium (Table 111). The metals which have lower D,values than that of nickel can be separated from calcium. Nickel seems to be a limiting element for the complete separation (Figure 4). Cadmium, copper, and cobalt ought t o be eluted between magnesium and calcium and enter both fractions. However these elements can very easily be separated beforehand by Kraus’ method (9), as can zinc, iron, and manganese.
(1) Campbell, D. K., Kenner, C. T., ANAL.HEM. 26,560 (1954). (2) Faris, J. P., Warton, J. W., Ibid., 34, 1077 (1962). (3) Fritz, J.’ S., Garralda, B. B., un-
published data.
(4) Fritz, J. S., Pietrzyk, D. J., Talanta 8,143 (1961). (5) Fritz, J. S., Rettig, T. A., ANAL. CHEX 34, 1562 (1962). (6) Honda, M., Bunseki Kagaku 3, 132 (1954). (7) Kojima, M., Ibid., 7, 177 (1958). (8) Korkisch, J., Tera, F., ANAL.CHEM. 33, 1265 (1961). (9) Kraus, K. A., Moore, G. E., J . Am. Chem. SOC.75, 1460 (1953). (IO) Lure’e, Yu. Yu., Stefanovich, S.N., Zavodsk. Lab. 13. 660 (1947): C. A . 42. 7464 (1948). (11) Nelson, F., Kraus, K. A,, J . A m . Chem. Soc. 77,801 (1955). (12) Tera, F., Korkisch, J., Hecht, F., J . Inorg. Nucl. Chem. 16,345 (1961). (13) Tsubota, H., Kitano, Y., Bull. Chem. SOC.Japan 33,770 (1960). (14) Wiinsch, L., Chem. Listy 51, 376 (1957). (15) Yoshino, Y., Kurimura, Y., Bull. Chem. SOC.Japan 30,563 (1957). \
I,
RECEIVEDfor review January 18, 1963. Accepted May 6, 1963. Contribution 1252. Work performed in the Ames Laboratory of the U. S. Atomic Energy Commission.
VOL 35, NO. 8, JULY 1 9 6 3
1083
