Quantitative Separation of HaIate Mixtures by Ion Excha nge Chro matog ra p hy JERRY L. SKLOSS, JOSEPH A. HUDSON,' and CHARLES J. CUMMISKEY Department of Chemistry, St. Mary's University, San Antonio, Texas A trimethyl benzyl ammonium anion resin (Dowex 21 K) and a dimethyl ethanol benzyl ammonium anion resin (Dowex 2), both in the nitrate form, have been used to effect a separation of sodium halate salts in millimolar quantities. The proportions were: (Na1O3:NaBrOz:NaClO3 1 :4:4)in the former case and ( 1 : 1 :15) in the latter case. The eluant was sodium nitrate in concentrations of 0.5 and 2.OM. Qualitative and quantitative verifications are given. The order of elution is the reverse of that for the simple halides under similar conditions on Dowex 1 .
A
PROCEDURES for the determination of mixtures of halates have been limited to iodate and bromate in the presence of chlorate (6, 7). Since the stepwise oxidation of iodide solution at carefully controlled p H is involved, the conditions are rather restrictive. Further, a considerable previous knowledge of the mixture composition is necessary to be able to properly adjust the amounts of reagents. The relative affinities of the halates on the resin Dowex 2 have been determined previously ( 5 ) . It has been possible to achieve a relatively simple and clean-cut separation of the halate anions by methods analogous to those already available for the simple halides NALYTICAL
(1). EXPERIMENTAL
Apparatus and Reagents. RESINS. T h e resins used were Dowex 21K, 50-100 mesh, and Dowex 2 X 8, 100-200 mesh. Both resins were t h e Analyzed Reagent grade supplied b y J. T. Baker Chemical Co., Phillipsburg, N. J. Dowex 21K is a n improved form of Dowex 1 b u t its crosslinkage is not defined. Because t h e resin was of high grade, it was treated to remove fines and was washed with the de-ionized water until colorthrow ceased. It was then converted from the chloride form as received to the nitrate form by washing with 0.5M N a N 0 3 until the eluant was free of chloride (-500 ml. at 2 ml./min.). 'Present address, Department of Chemistry, University of California, Berkeley, Calif.
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ANALYTICAL CHEMISTRY
The resin samples were used through several cycles. SALTSAND i i c ~ ~ sSalts . and acids were all AR chemicals and were used without further purification. The halate stock solutions were: 0.5000X NaC108 and 0.5.11 N a N 0 3 ; 0.5000111 NaBr03 and 0.5M x a x O 3 ; and O . l O O O J 1 NaIO3 and 0 . 5 X rc'aNO3. ORGANICREAGENTS. The diphenylamine was the highest purity material available from Eastman Organic Chemicals and the starch was the J. T. Baker's Reagent for Iodometry. COLUMNS. The chromatographic elution studies were carried out in columns supplied by Fischer and Porter Co. The stopcocks were Teflon. The standard method of obtaining a constant head with an eluant reservoir was employed (2). Column dimensions were 2 sq. cm. X 13 cm. and 6.15 sq. cm. X 23.5 cm. or X 28 cm. in the case of Dowex 21K and 6.15 sq. cm. X 28 cm. for the Dowex 2 runs reported. Procedure. PACKING OF COLUMN. T h e resin was introduced into t h e column as a n aqueous slurry, agitated with a stirring rod, and allowed to settle to the required height. I t mas topped with a disk of Whatman KO. 1 filter paper t o keep i t in place during t h e addition of samples and t h e elution process. I t s vertical alignment was checked with a level. INTRODUCTION OF SAMPLES. The packed columns were converted t o the nitrate form in situ. The eluant was drained until i t was within a few mm. of the top of the resin (this is the point designated as 0 ml. in the elution data). The specified amounts of the three halates were introduced using suitable pipets and the stock solutions. The mixture was then drained into the resin bed. Finally, 0.5M ?I'ah'03 eluant was introduced so t h a t the liquid level was about 2 cm. above the resin. The eluant reservoirs were connected and the flow rate was adjusted as desired. ELUTION. After the iodate had been eluted, the flow rate was increased so as to shorten the time for the complete process. Increasing the concentration of the nitrate from 0.5.11 to 2.0M just before the bromate had been completely eluted was advantageous to minimize bromate tailing and to speed up the chlorate elution. QUALITATIVE TESTS. Qualitative tests were employed to determine the halate regions in the elutions. TO identify the species in each region, specific spot tests were made as outlined
in Feigl ( 4 ) : KSCN and starch paper for iodate; MnSOc and H2S04 for bromate; and ;\lnS04 and H3P04for chlorate. These tests though specific are not very sensitive, so in establishing the limits of the various regions the more sensitive but nonspecific acidiodide-starch test for iodate and bromate and a n acid-diphenylamine test for chlorate were employed. The former test consisted of adding two drops of starch solution (in which iodide ion was present) to an acidified 2-drop sample of eluate on a spot plate. I t was established by dilution that the characteristic I*-starch deep blue chloration was detectable for 1 0 3 - and & 0 3 concentrations down to l O - 7 V . The test for chlorate consisted in adding two drops of a saturated solution of diphenylamine dissolved in concentrated HC1 to a 2-drop sample of eluate on a spot plate. *in instant violet coloration indicated a positive test (8). The limit of the test, also established by dilution, was 2 X l O - 4 M . QUAiYTITATIVE RECOVERY VERIFICATION. The quantitative tests employed for the verification of the recovery of halate species in the elution regions were as follows. Iodate. The eluted iodate ion present in the indicated volume region of eluant was determined by reaction with acidic K I to yield Iz. The sample was then titrated immediately with standard 0.LV Na2SzO3 to the starch end point. Bromate. The eluated bromate ion present in the indicated volume region of eluant mas determined by reaction with acidic K I to yield 1 2 after the removal of dissolved air with KaHCO3 (8). The sample was then titrated immediately with 0.1S Na2S203to the starch end point. Chlorate. The eluted chlorate ion present in the indicated volume region of eluant was determined by reduction to chloride with ferrous sulfate. The solution was acidified with HS03 to dissolve the Fe(II1) precipitates. This step required 5 hours when heated on a steam bath. K h e n the solution was clear, AgCl was Ixecipitated and determined gravimetrically. RESULTS
Table I shows the regions of positive qualitative test for the individual halate species when taken separately on Dowex 21K. There is an overlapping of the first two regions indicated.
Table
I. Individual Halate Species Elution on Dowex 21 K
Resin bed: 2 sq. em. X 13 cm. Flow rate: 2 ml./min. Eluant: 0.5.11 NaN08 Ranges of positive tests: T O 3 - 20-35 ml. Br03- 30-75 ml. C10,- 77-150 ml.
Table 11. Effect of Flow Rate on Iodate-Bromate Mixture Separation on Dowex 2 1 K Employing Increased Resin Bed
Resin bed: 6.15 sq. cm. X 23.5 em. Eluant: 0.5M ?I’aNO? Flow rate: 3.5 ml./min. Ranges of positive tests: IO3- 90-153 ml. Br03- 155-350 ml. Resin bed: Same as above Eluant: Same as above Flow rate: 2 ml./niin. Ranges of positive tests: Io3- 90-155 ml. Br03- 170-330 ml.
Table I1 shows the beneficial effect of greater resin bed and slower flow rate on the separation of a mixture of the more difficult to separate iodate and bromate ions. The component of each region was verified by the specific spot tests and the regional boundaries were verified by the more sensitive spot tests at 1-ml. intervals. The same is true of subsequent mixture separations. The regions from a successful separation of a mixture of all three halates were determined by the above qualitative tests during elution and are shown in Table I11 for both Dowex 21K and Dowex 2 X 8. Quantitative analyses for the recovered halate species after fractionation were made to check material balance. The results of three separate runs are given in Table TV for both Donex 21K and Dowex 2 X 8. DISCUSSION
LITERATURE CITED
The order of selectivity of the resins for the halates is the opposite of that for
Table 111. Separation of Halate Mixtures Resin: Dowex 21K Resin bed: 6.15 sq. cm. X 28 cm. Eluant: S a x 0 3 0.5M to 370 ml.; 2.0M beyond Flow rate: 2 nil./min. to 200 ml.; 3 ml./min. beyond Ranges of positive tests: 10,- ( 0 4 mmole) 80-185 ml. BrOa- (1 0 mmole) 195-390 ml. c103- (1 0 mmole) 450-650 ml. Resin: Ilowex 2 X 8 Resin bed: 6.15 sq. em. X 28 em. Eluant: NaN03 0.5M to 270 ml.; 2.0M beyond Flow rate: 2 ml./min. Ranges of positive tests: IO3- ( 0 . 1 mmole) 50-200 ml. Br03- ( 0 . 1 mmole) 205-380 ml. c103- (15 mmole) 410-620 ml.
Table IV.
Halate species Found IO3- Theo. Diff. Found BrO3- Theo. Diff. Found C103- Theo. Diff.
Found IO3- Theo. Diff. Found BrOs- Theo. Diff. Found C103- Theo. Diff.
0,400
- 0.001
1.001 1,000 0.001
0,988 1,000 -0,012
Dowex 21K RLUIIT 0.400 mmoles 0.400
Run 111 0.399 mmoles 0.400 -0.001
0,001
1.002 1,000 0.002 1.003
1.003 1,000 0.003 1.002
0.002
1,000
1,000 0.002
-
Dowex 2 Run B 0,098 mmoles
Run C 0.098 mmoles
0,098 0.000 0.100
0.098 0.000
0,098 0.000
0.100 0.100
0.100 0.100
Run A 0.098 mmoles
0.100
0.000
0.000
1.495 1.490
1.497 1,490
0,005
Mean abs. diff. from theoretical
0.000
0.003
0.007
0.000
1.496 1.490 0.006
(1) DeGeiso, R. C., Rieman 111, W.,
Lindenbaum, S., ANAL. CHEM., 26, 1840 (1954). (2) Dow Chemical Co., hli$and, Mich., “Dowex: : I o n Exchange, p. 48 $., 1958. (3) Ibid., p. 9. (4) Feigl, F., “Spot Tests,” Vol. I, Inorganic Applications, p. 274$., Elsevier, Houston, 1954. ( 5 ) Kinkindai, AI., Compt. Rend., 237, 250-2 11953’1. (6) Kolthoff, -1. hl., Belcher, R., “Volumetric Analysis,” Vo1. 3, p. 268 $., Interscience New York, 1957. (7) Kolthoff, I. &I., Hume. D. N.. IND. ENG.CHEM.,ANAL.ED. 15, 174 (1943). (8) Pierce, W. C., Haenisch, E. L., Sawyer, D. T., “Quantitative Analysis,” 4th ed., pp. 225, 300, Wiley, New York, 1958.
Recovery of Halates after Fractionation of Mixtures
Run I 0,399 mmoles
the simple halides. This is in agreement with the relative affinity series deduced from determinations of equilibrium coefficients of these species on Dowex-2 by Kikindai (6). Since the factor affecting selectivity which seems to be relevant here is the size of the hydrated ions (S), the following inferences are made. I n the case of the simple halogens, the charge density decreases from C1- to I- and thus minimizes the extent of hydration. The net effect is that the overall size of the hydrated simple ions is Cl-aq largest to I-aq smallest. In the case of the halate anions there is not much difference in the charge density and so hydration is not significantly different. Thus the size of the hydrated halates goes in the same order as that of the unhydrated simple ions making the largest and C103-,, the smallest.
RECEIVEDfor review April 12, 1965. Accepted June 22, 1965. Work supported by Grant No. 6-8406 of the National Science Foundation. J. L. Skloss was an undergraduate participant in a National Science Foundation Program in Undergraduate Science Education. J. A. Hudson was an undergraduate participant supported by the Department of Biochemistry of the Southwest Foundation for Research and Education.
Correction 0.006
0.000 0.000
0.006
Measure ment of Proton Relaxation Times with a High Resolution Nuclear Magnetic Resonan ce Spectrometer I n this article by Van Geet and Hume
[ANAL. CHEM. 37, 983 (1965)l an error appears in Equation 37 on page 988. The symbol 6 should be z. VOL. 37, NO. 10, SEPTEMBER 1965
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