250 11.p.m. of NO3-) utilizes 2-phenylpyridyl ketoxime. The timing of reagent addition and the time of absorbance measurement are much less critical with this ligand. It is anticipated that other metal ions in this area of the periodic table, such as Mo, W, and Tc, will also show this behavior. Preliminary experiments show that Mo is potentially useful in this respect and a method may be capable of developmeiit using this metal ion. This technique may also be useful for the determination of c103-,since it is as effective as Nos- in preventing color formation. Finally, it should be mentioned that the amount of rhenium used per analysis is very small. One gram of KRe04 is capable of conducting over 2000 analyses. ACKNOWLEDGMENT
We are indebted to L. J. Forrestor, H. N. Kirkpatrick, and W. R. Scheidt for their assistance.
LITERATURE CITED
i l i Anuiar de Carvallio. L. F.. Anais ‘ Ass& Brasil Quim. ’9, 106 ’ ( 1 9 5 0 ) ; C.A. 46, 668 (1952). ( 2 ) Allerton, F. W., Analyst, 72, 349 (1947). ( 3 ) Banerjea, D., Mohan, M. S., J . Indian Chem. SOC.40, 188 (1963). (~, 4 ) Buckett. J.. Duffield. W. P.. Milton, R. F., Anal& 80, 141‘(1955).’ ( 5 ) Chamat, E. M., Pratt, D. S., Redfield, H. W., J . Am. Chem. Soc. 33, 366 (1911). ( 6 ) Fergusson, J. E., Gainsford, J. H., Znorg. Chem. 2, 290 (1964). (‘7) Garner, G. B., Baumstark, J. S., Muhrer, M. E., Pfander, W. H., ANAL. CHEM.28, 1584 (1956). (8) Haight, G. P., Jr., American Chemical
Society Meeting, Physical Division, New York, 1963. ( 9 ) Haller, A. C., Huch, R. V., ANAL. CHEM.21, 1385 (1949). (10) Hartley, A. M., Asai, R. I., Ibid.,
35, 1207 (1963). (11) Jenkins, D., Medsker, L. L., Zbid., 36, 610 (1964). (12) Maun, S. K., Davidson, N., J . Am. Chem. SOC.72, 2254 (1950). (13) McVey, W. C., J . Assoc. Ofic. Agr. Chemists 18, 459 (1935).
(14) Meloche, V. W., Martin, R. L., Webb, W. H., ANAL.CHEM.29, 527 (1957). (15) Murtz, G. V. L. N., Proc. Indian Acad. Sci. 14A, 4 3 (1941); C.A. 36, 1562 (1942). (16) Nelson, J. L., Kurtz, L. T., Brag, R. H., ANAL. CHEM. 26, 1081 (1954). (17) Reitemeier, R. F., IND.ENG.CHEM., ANAL. ED., 15, 393 (1943). (18) Taras, 11. J., ANAL.CHEM.22, 1020 11950). (19) Taras, >I. J., J . Am. Water Works Assoc. 45, 47 (1953). (20) TribElat, S., “Rhenium et Tech-
nitium, Gauthier-Villans Editeur-Imprimeur-Libraire, llonographies de Chemie Physique (1957). (21) Werr, F., Z. Anal. Chem. 109, 81
(1937). (22) Woodward, P., Analyst 78, 727 (1953). (23) Yagoda, H., IND. ENG. CHEM., ANAL.ED. 16, 4661 (1944).
RECEIVEDfor review May 14, 1964. Accepted November 23, 1964. Investigation supported in part by research grant GP-585 from the National Science Foundation and by research grant Alf-07303 from the National Institute of Arthritis and Metabolic Diseases, U.S.P.H.S.
Quantitative Separation for Magnesium, Calcium, and Strontium Using Zirconium Molybdate Ion Exchange Crystals MILTON H. CAMPBELL Chemical Processing Deparfment, General Electric Co., Richland, Wash.
b Alkaline earths can b e quantitatively separated on zirconium molybdate ion exchange crystals. M a g nesium is eluted with 0.1 4M ammonium sulfate made up in 60 volume per cent methanol. Calcium is eluted with 0.2M NH4NOa-0.005M HNOL and strpntium is eluted with 1M NH4N03. The sample loading matrix may b e between p H 2 and pH 12 and may contain limited quantities of (ethylenedinitri1o)tetraacetic acid (EDTA). The effects of diverse ions on the loading and elution phases of the separations are discussed. Chemical yields ‘for magnesium, calcium, and strontium mixtures of varying compositions are presented.
’
T
’
HE FIRST FISSION product isotope produced. a t the Hanford Atomic Products Operation was strontium-90. Since then, this isotope has been used extensively in the SyFtems for Suclear Power (SSAP) Program ( 5 ) . Recently, an intensive program has been carried out to incrcwe the specific acitivity of the strontiuin-90 product. Two of
252
ANALYTICAL CHEMISTRY
the significant contaminants are nonradioactive magnesium and calcium. An analytical procedure was needed that was capable of separating these impurity elements from highly radioactive solutions of strontium-90-yttrium-90 and cerium 141-144-preseodymium-144. Classically, magnesium, calcium, and strontium have been separated by their solubilities ( 4 , f a )as chromates, nitrates, oxalates, and sulfates. I n general, these methods are tedious and not suited to manipulations with intensively radioactive samples. Extraction procedures have also been applied to these separations. Thenolytrifluoracetone (6) is reported to extract strontium from yttrium, but, in the author’s experience, clearcut separations from calcium are not possible. Di(2-ethylhexy1)orthophosphoric acid (If) has been utilized in separating alkaline earths from rare earths and yttrium, but separation of individual alkaline earths is not easily achieved. Solubilities of the alkaline earth salts (IO) in various organic chemicals will afford some separations,
but these methods do not lend themselves to highly radioactive samples. Ion exchange techniques have been used extensively to separate the alkaline earths and magnesium. I n the case o t cation exchange systems, complexants such as citrate ( I S ) , lactate ( 8 ) , and (ethylenedinitrilo) tetraacetic acid (EDTA) (2, 1 4 ) are commonly used as eluents. The resulting fractions of pure elements are not readily measured quantitatively unless they are radioactive isotopes, or flamophotometric methods can be applied. The latter technique is not acceptable in radioactive systems because of the severe airborne contamination that is created. Fewer anion exchange separations have been reported. Fritz, Waki, and Garralda (3) recently described a separation for magnesium, calcium, and strontium with an anion exchange resin of rapid sorptive rate using nitric acidalcohol mixtures as eluents. Properties of synthetic inorganic exchange crystals have been the subject of a number of recent papers. A collection of these papers is available ( I ) . Absorption data for 60 metal ions
on four inorganic ion exchangers from nitrate media were compiled by Maeck, Kussy, and Rein ( 9 ) . Kraus, Phillips, Carlson, and Johnson ( 7 ) reported an alkaline earth separation on zirconium molybdate using ammonium chloride in increasing concentrations as an eluent. Separations were achieved by solubilities of the element's in this salt solution, thus permitting the use of relatively short ion exchange columns and low eluent volumes. Additionally, the purified fractions could be measured q w t i t a t i v e l y by a variety of methods with no interference from the eluent. L-nfortunately, the amount of chloride that can be introduced into the radioactive waste streams of the local separations plants is restricted because of the corrosion potential. The purpose of this inyestigation, therefore, was to find a substitute eluent, other than a complexant, and to further expand the separation to include magnesium. EXPERIMENTAL
Column. T h e zirconium molydate
ion exchange crystals (Zm-1, Bio-Rad Laboratories) are available in a 100 to 200 mesh size. These crystals are more fragile t h a n organic resins and tend to powder to some extent on handling or from packing in t h e storage bottle. T h e resulting fines can be easily floated off by agitating with a fine stream of distilled water (agitating with a stir bar breaks the crystal). The crystals are prepared daily as needed; they should not be stored from day to day under dist'illed water. Columns are made of 5-mm. glass t'uling, 10 cm. long with a dropper tip on the lower end, and a 25-ml. reservoir a t the top. A small glass wool plug is inserted to support the crystals. The wetted crystals are loaded by gravity in a column full of water until a bed 8 cm. high is prepared. The exchange crystals are not intentionally packed. However, some packing will occur during sample loading and elution, and, additionally, the crystals are slightly soluble, so a 0.5-cm. shrinkage in bed height is usual during t'he Zirconium molybdate crystals dissolve below p H 1, above p H 12, or in oxalate, citrate, and strong E D T A solutions. Reagents and Solutions. d m m o nium sulfate, ammonium nitrate, methanol, nitric acid, a n d E D T A ( X a salt) were all reagent' grade and no further purification was made. Stock solutions of magnesium, calcium, strontium, and barium were all prepared by dissolving weighed quantities of their nitrates in distilled water. I n addition to the weight make-up, their concentrations were verified by titration with a standard EDT.4 solution. Procedure. Pretreat the bed by passing 10 ml. of 2.11 ammonium nitrate through just prior to use. Add a 3-ml. distilled water wash when the ammonium nitrate has drained t o the surface of the exchange
crystals. T h e column flow should be about 0.75 ml. per minute. Add a sample, not to exceed 5 ml. in volume, to the reservoir. The sample should contain not more than 0.05 mmole, combined, of magnesium, calcium, strontium, and barium, and no more than 0.025 mmole of any individual element. Discard the sample raffinate as well as a subsequent 3-ml. water wash. (Samples containing E D T A or sodium hydroxide require a 20-ml. or 10-ml. water wash, respectively.) Elute each fraction directly into a preblanked ammonium hydroxideammonium chloride buffer (pH 10) and titrate with a standard 0.005-I4 E D T A to the Erichrome Black T end point. Elute the magnesium fraction with 7 ml. of 0.14Jf (SH4)&304-60% methanol. The column reservoir must be covered with a watch glass during this operation to reduce alcohol evaporation. Elute calcium with 20 ml. of 0.2.11 ~ H 4 ~ 0 3 - o . 0 0 5 A k"03, f or if the sample contained EDTA, elute with 15 ml. of the same reagent. Elute the strontium with 5 ml. o r l M SHJOI.
Table I. Apparent Capacity of Zirconium Molybdate Ion Exchange Crystals as a Function of Pretreatment
",NOS molarity in pretreatment solution 0 0 0 5M 1 OM 2 OM 4 OM
Crystal
Mmole PiH4?J03
ml. ZM-1
0 3 6 12 25
18 37 73
46
(meq. Mglml.
ZM-1) 0 184 0 200 0 200 0 205 0 206
treatment with ammonium nitrate stabilized the apparent capacity as shown in Table I. Although these capacity changes appear to be small, the exchange crystals must be stabilized to provide consistent recoveries for the small bed sizes used. A 25i' XH4?;03 solution was selected for pretreatment since it imparted an apparent capacity almost equal to the 4 X solution and dissolved much less of the exchange crystals. Pretreatment with ammonium nitrate also improved separations between calcium and magnesium. Figure 1 illustrates this effect.
RESULTS A N D DISCUSSION
Exchange
Apparent capacity
Pretreatment.
T h e exchange crystals, as received, are in the acid form. T h e apparent capacity, found by loading the bed to breakthrough, changed as t h e nitrate content of the sample changed. Pre-
Magnesium-Calcium-S t r o n t ium Separation. Separation was first
tried with eluents of varying ammonium nitrate concentrations. The qep-
A: No P r e t r e a t m e n t
4
I-
2
0 'C
.^ ' 6 0
-
4
L
c
" z
V
2
-n
> u
2
0
p:
4
m, I-
6 : 0.4 mmoles NH4N03 P r e t r e a t m e n t
;:
LC:4.0
I
mmoles NH4N03 P r e t r e a t m e n t
2
0 0
1
2
3
4
m l E l u e n t (O.lM NH4N03-0.005hJ
5 HN03)
Figure 1 . Effect of exchanger pretreatment on calcium and magnesium separations 5 mm. 1.d. X 4 cm. Flow rate. 0.75 ml. per min. Mg. 0.01 mmole. C a . 0.01 mmole
Column.
VOL. 37, NO. 2, FEBRUARY 1965
8
253
~~~
~~
Table 11. Quantitative Separation of Magnesium, Calcium, and Strontium Mixtures Sr_(mmolesp Mg (mmoles)= Ca (mmoles)b _ _______ Error Taken Found Error Taken Found Error Taken Found Standard -0 0004 0.0228 0 0224 0.0003 0 0102 0 0104 0 0002 0 0094 0 0091 A 0 0005 0.0007 0,0228 0 0223 B 0 0019 0 0018 -0 0001 0 0188 0 0181 -0 0008 0.0228 0 0220 0.0 0 0022 -0 0001 0 0022 0 0163 C 0 0164 -0 0001 0.0228 0 0227 0 0020 0 0020 0 0 n 0020 0 0 n no20 D -0 0001 0.0114 0 0113 - 0.0002 0 0001 0 0092 0 0090 E 0 0102 0 0101 0 0002 0.0020 -0.0001 0 0020 0 0020 0 0021 0 0001 0 0192 0 0191 F a Eluent: 7 ml. of 0.14M (NH4),S04-6O7, by volume methanol. * Eluent: 20 ml. of 0.2M NH4NO3-0.005M HXO3. c Eluent: 5 ml. of 1.OM "4N03.
aration factors were calculated using recthe equation S = VmaxA/Vmax~, ommended by Fritz (3). A good separation factor (3.3) was achieved using 10 column volumes of 0.08X "4~03-0.005hf HxOs for magnesium and then 10 column volumes of 0.2M "4N03-0.0()5.\f HN03 to elute the calcium. Unfortunately, a high strontium contamination appeared in the last three column volumes of the calcium fraction. Increasing the height of the column a factor of 1.5 did little to improve the separation, although it did materially reduce the flow rate. An eluent was needed in which strontium salts were less soluble. An amnionium sulfate syst'em was also investigated. Good magnesium and calcium separations were found. A separation factor of 4.0 was found using four column volunies of 0.1M (NH&S04 for magnesium and six column volumes of 0.15:cI (NH4)tSOd0.1JI HN03 for calcium. Presence of strontium on the column presented a problem, however, since strontium sulfate precipitated and materially reduced the eluent flow rate to 0.05 ml. per minute. To promote a faster flow rate during the magnesium elution, methanol was used to make u p a 0.14M ammonium sulfate solution. While the ammonium sulfate is insoluble in alcohol. tests showed this concentration was quite soluble in a 60% alcohol-40yo distilled water misture. Jlagnesium was eluted completely within five column volumes with no calcium interference. The elution rate was quite rapid (0.6 ml. per minute) with no apparent slowing, even under high strontium loading conditions. Figure 2 shows this elution as well as the subsequent elution of calcium, strontium, and barium. A dotted line was used to indicate elution of calcium when addition of the 0.14.1fammonium sulfate-60y0 methanol was continued. The ion eschange column reservoir had t,o be covered so only a minimum amount of the alcohol eyaporated. Calcium elution was observed when the alcohol content was less than 50%,. Calcium elution with alcoholic solutions of either ammonium sulfate or ammonium nitrate was very slow. On
254
e
ANALYTIEAL CHEMISTRY
the other hand, any aqueous concentration of ammonium nitrate above 0.1M would remove calcium from the column; however, concentrations above 0.4.V also eluted the strontium almost simultaneously. Vsing a 0.2.11 ammonium nitrate solution, the calcium was selectively eluted, although five column volumes were added before elution began. A separation factor of 5 was found between calcium and magnesium. Traces of strontium were detectable two column volumes after completion of the calcium elution as shown by the dotted line in Figure 2. Strontium was rapidly removed from the crystals with four column volumes of molar ammonium nitrate. On this basis the separation factor between calcium and strontium would be 1.6. However, when the 0 . 2 X ammonium nitrate elution was continued, a separation factor of 2.3 was observed. A set of standards containing varying quantities of magnesium, calcium, and strontium was prepared to evaluate the elution under different loading conditions. Table I1 shows the recoveries attained were consistent even when traces of these elements were present. All standards were analyzed a t least three times, and the data presented re1~resent the averages and their error.
Table 111. Effect of Diverse Ions on Zirconium Molybdate Loading with Alkaline Earths and Magnesium
Mmoles at Remarks Ion breakthrough 0.15 pH = 1.60 Hf 0.30 Used as NaNO8 Xa EDTA 0.06 Used as the sodium salt; 0.06 mmoles visibly dissolve the crystals Citrate 0.02 Used as the sodium salt; 0.02 mmoles visibly dissolve the crystals Fe + 3 0.02 Ce +s 0.01 OHSotdetected Used as the sodium salt; pH a t 0.04 = 12.0 mmoles
Effects of Diverse Ions. While t h e separation worked very well in aqueous solutions, the sample matrices to be considered are not t h a t simple. The presence of other ions had a significant influence in the loading properties of the resin. For the purpose of this test, a n alkaline earth breakthrough on a column half the
0 . 1 4 h ~ NH41 S O4 - 6 0 % M e t h a no I \
/
"
c -; 12
Flow Rate: 0.6-0.75 m l l m i n .
e L C
Mg: 0.01 m m o l e s
0
U u
Ca: 0.01 m m o l e s
E a
S r : 0.023 m m o l e s
E a : 0.020 m m o l e s 4
0 0
5
10
15
20
25
30
35
Column V o l u m e s
Figure 2. barium
Elution curve for magnesium, calcium, strontium, and
40
~
Table IV. Quantitative Separation of Magnesium, Calcium, Standard Mg- (mmo1es)a Ca composition Taken Found Error Taken O01M EDTA 0 0102 0 0102 0 0 0 0094 0 0 0 0020 0 0020 0 0192 (Na salt) -0 0002 0 0094 0 001~f 0 0102 0 0100 -0 0001 0 0192 0 0020 0 0019 NaOH a Eluent: 7 ml. of 0.14M (NH4)*SO4-6O%by volume methanol. Eluent: EDTA sample: 15 ml. of 0.2M NH4N03-0.005M "0s. SaOH samDle: 20 ml. of 0.2M NH4N03-0.005M "01. ~~~
length used in the analysis would result in incomplete separations. Table I11 lists the ions considered and the limiting concentrations found. Since the elements of interest can be recoveied from EDTA and caustic solutions, standards were prepared in these matrices and these yields appear on Table IV. A larger water wash volume was required for these samples, not only to remove traces of the complesant, but also to remove all the zirconium molybdate that was dissolved. Inl the case of sodium hydroside, the wash volume required was 10 ml., and the elution sequence mentioned previously was applicablf>. I n the case of EDTA, however, a water wash volume of 20 nil. was needed prior to elution. The sequence was also altered somewhat as shown in Figure 3. Magnesium was eluted slower, while calcium was rapidly removed within 15 column volumes. I n fact, the use of 20 column volumes eluted some of the strontium. I n the elution phase neither iron nor cerium interfered seriously in the analyses, when they were present up to 0.001 mmole. Zinc, lead, and copper could also be tolerated a t this level, but nickel interfered in the magnesium fraction a t any detectable concentration. LITERATURE CITED
(1) Bio-Rad Laboratories, Richmond, Calif., Bulletin: Selected References on Synthetic Inorganic Exchangers (1962). (2) Ilavis, P. S., A'ature 183, 674 (1959). (3) Fritz, James S., Waki, Herohiko,
and Strontium Mixtures in EDTA and N a O H Systems
(mmoles)* Found 0 0091 0 0190 0 0093 0 0194
Error -0 0003 -0 0002 -0 0001 0 0002
Taken 0 0228 0 0020 0 0228 0 0020
Sr (mmo1es)c Found Error 0 0225 -0 0003 0 0021 -0 0001 0 0220 -0 0008 0 0022 0 0002
0.14M ( N H 4 ) 2 S 0 4 - 6 0 % Methanol
0.2M NH4NOj-0.005M HNO
3
1
C o l u m n : 8 c m x 5 m m I. D. F l o w R a t e : 0.6-0.75
mllrnin.
Mg: 0.01 m m o l e
Ca: 0.01 m m o l e
2
0
4
6
0
10
12
14
16
18
Column Volumes
Figure 3. EDTA
Elution curve for magnesium and calcium when sample is 0.01 M
Garralda, Barbara B., ANAL. CHEM.
36, 900 (1964).
(4) Furman, N. H., "Scott's Standard ,Methods of Chemical Analysis," 6th ed., T'an Sostrand, Sew York, 1962. (5) General Electric Co., Richland, Wash., Bulletin: Fission Products (1964). (6) Kiba, T., Miaukami, S., Bull. Chem. SOC.Japan 31, 1007 (1958). (7) Kraus, K. A., Phillips, H. O., Carlson, T. A,, Johnson, J. S., Second United Nations Conference on Peaceful Uses of Atomic Energy, Geneva, 1958, Paper 1832. (8) Lerner, hl., Rieman, W., 111, ANAL. CHEM.26, 610 (1964). (9) Maeck, W. J., Kussy, M. E., Rein, J . E., Ibid., 35, 2086 (1963). (10) Morrison, G. H., Freiser, H., "Sol-
vent Extraction in Analytical Chemistry," Wiley, New York, 1957. (11) Peppard, D. F., Mason, G. W., Moline, 6. W., J . Inorg. Wucl. Chem. 5, 141 (1957). (12) Sunderman, D. N., Townley, C. W., NAS-NS 3010 (1960). (13) Tompkins, E. R., J . Am. Chem. SOC. 70. 3520 (1948). (14) 'Wade, ' M. A,,Sein, H. J., ANAL. CHEM.33, 793 (1961). RECEIVEDfor review October 9, 1964. Accepted November 19, 1964. 19th Annual Xorthwest Regional Meeting, ACS, Spokane, Wash., June 1964. Work performed under Contract No. AT(45-1) 1350 between the Atomic Energy Commission and General Electric Go.
VOL. 37, NO. 2, FEBRUARY 1965
255
