Ion Exchange Chromatography Harold
I
F. Walton,
Department of Chemistry, University o f Colorado, Boulder, Colo.
the number of publications is a n y criterion, research in ion exchange chromatography continues a t a steady and perhaps accelerating pace. The most significant developments, possibly, are in the area of column design and instrumentation. There are signs that liquid chromatography will find increased use in the immediate future, thanks to automatic control and methods of column monitoring. Thus, the time required for amino acid analysis has been cut in half b y the use of ligand exchange coupled with close control of operating conditions (18). Rapid flow techniques and the use of narrow columns are among the recent developments. The use of mixed aqueous-nonaqueous solvents noted in our last review has increased considerably and has added a new dimension to inorganic ion exchange chromatography. There is a rebirth of interest in resins containing selective functional groups, and this is paralleled b y the development of new inorganic exhangerq, especially those of the ferrocyanide type. At the same time the basis of qelectivity in inorganic exchangerh is becoming better understood. ;\nother interesting development i q the uye of liquid ion exchangers, incorporated into a suitable solid support and used as the stationary phase in column and thin-layer chromatography. Interest in paper and thin-layer chromatography is increasing, in part because of the development of ion exchanging materials based on cellulose and deytran. While gel permeation chromatography qcarcely comes within the scope of this review, it must be noted t h a t t h e developinelit of this technique has lead to a better understanding of the physical structure of polymers and natural materials of high molecular weight. Applications t o inorganic analysis continue to emphaqize heavier elements, fishion-product mixtures, and the technology of atomic energy. Ion exchange is also w e d to concentrate and separate trace impurities in high purity materials. Turning to applications in organic and biochemistry, many publications are noted which deal with carbohydrate mixtures, pharmaceutical products, and derivatives of DKA. This review does not pretend to list all of the publications t h a t mention biochemical uses of ion exchange chromaF
tography, but the hope is expressed t h a t our selection of references is a representative one. M a n y important papers on the nature of the ion exchange process have appeared in the last two years b u t these are not cited unless they have a direct bearing on chromatography. BOOKS, REVIEWS, JOURNALS
The book “Analytical Applications of Ion Exchangers,” by Inczedy, previously published in Hungarian and German, has now appeared in a n English edition (156). I n the 1966 review we overlooked a useful book by Dorfiier (106), which in 211 pages provides a surprising amount of information, with tables of commercial resins including those of Russian manufacture, a concentrated summary of chromatographic separations, and a good theoretical section on the thermodynamics and kinetics of ion exchange. -%notherGerman book describes column chromatography on cellulosic exchangers (300), with special reference to biochemical applications. The new edition of Heftmann’s “Chromatography” (14Sa) is up-todate and contains several chapters devoted to ion exchange methods, contributed by different authors. -% series of volumes on advances in ion exchange is planned, and the first, edited b y Marinsky, has appeared (227). The series ‘l-ldvances in Chroniatography” (133) began in 1966 and now includes five volumes; the first chapter of the first volume was on ion exchange chromatography (by Helfferich) ; chapters on amino acid qeparation appeared in Volume 2, on cellulosic exchangers in Volumes 4 and 5 . A recent volume of “Progress in Suclear Energy” (334) contains a comprehensive review of ion exchange chromatography in organic solvents by Korkisch, and a review b y Faris on anion exchange in nitrate solutions. The journal Separation Science started publication in 1966 (Xarcel Dekker, Inc.) and includes contributions on ion exchange. Among general reviews of ion exchange chromatography that have appeared in the literature may be mentioned a review of carbohydrate and acid separations b y Samuelson (302) and a review of new chromatographic separations of metals by Chernobrov (85).
80304
THEORY
A novel treatment of column chromatography which indicates the trend of future developments appears in a paper by 1tangeladorf (225) entitled “Difference Chromatography.” The interaction of a number of components in a moving front is considered, where the absorption of one component depends on the concentrations of the others. A technique is described for the measurement of small differences in composition between two samples of sea water; a “plug” of the solution to be analyzed is inserted into a stream of the reference solution, and the front which develops at the end of the column is analyzed and recorded by measuring the electromotive force across ion exchange membranes. Other theoretical papers discuss a probability theory of elution bands (132), the operation of packed capillary columns in liquid chromatography (236), theoretical-plate height in the separation of lanthanides (232),gradient elution (258), and the movement of chromatographie bands in which the substance is undergoing first-order decomposition in the fixed and mobile phases (178). This last treatment applies to the chromatography of shortlived radioactive species as well as to the hydrolysis and isomerization of complexes. TECHNIQUES
A new method of monitoring column effluents which may have a great inipact on liquid chromatography was described by Hupe and Bayer (153). It depends upon the heat of absorption and desorption which accompanies the passage of a chromatographic band. The temperature senqor may be located in the column itself, but is more conveniently placed in a small chamber through which the effluent f l o w after leaving the column. This chaniber contains an absorbent which may be the same as that in the main column (such as an ion exchange resin) or may be another material. When an elution band passes the temperature first rises, then falls below its origirial value, then returns to the base line. (Of course this sequence is reversed if the absorption is endothermic.) This technique is very sensitive and perfectly general, applicable to all types of liquid chromatography, including ion exchange. VOL. 40, NO. 5, APRIL 1968
51 R
An improved reflection-type flowing refractometer has been described (161). Electrical conductivity of the resin (not the solution) is uqed to measure frontal development in displacement chromatography (141). Other electrical techniques, applied to the flowing solution, include measuring the potential across a membrane (2%), the current at a hanging mercury drop (170, ,9233, and the technique of square-wave polarography (65). An interesting feature of the latter is that overlapping elution bands can be tolerated provided the reduction potentials of the overlapping component.. are different. Other detection systems for organic compounds depend on evaporating the solvent from the effluent and either weighing the nonvolatile solute (210) or transferring it by a moving chain or wire to a pyrolysis chamber; the products of pyrolysis are then measured in a n ionization detector (166, 369). Automatic chemical analysis with reagents added through solutionmetering pumps is becoming commonplace, especially for organic and biochemical analysis (137, 162-164, 171, 238, 284, 289, 303, 316, 329, 371). Automated, accelerated analysis has brought with it a demand for resins that are uniform in particle iize and crosslinking, and the Sational Bureau of Standards has a program for producing such resins (129). There is a trend to the use of long, narrow columns with dimensions like those used in gas chromatography. Thus nickel and cobalt were separated by cation exchange in columns 0.3 m m X 128 mni (236). Sucleotides were separated on columns 1 m m X 150 cm packed with glass beads coated with a strong-babe anion exchange resin (a “pellicular ion exchanger”) ; this arrangement allowed fast flow rates and rapid separation of m a l l amounts of material (150). The operating pressure was 50 atm. A novel chromatographic technique combining ion exchange with solvent extraction is “extractive ion exchange.” Very sharp separations of the lanthanides were obtained by this method (216). The moving phase was a hexanol-thenoyltrifluoroacetoiie solution emulsified in a n aqueous solution of a-hydroxyisobutyric acid, and to keep the emulsion from separating, it was introduced into the column upflow in a stream of nitrogen bubbles. The column was divided into 40 segments by perforated plastic disks. Another novel technique i. “sublimation chromatography,” actually a kind of gas chromatography in which the vapors of aromatic amines are passed in a stream of air through a column packed with cellulose and montmorillonite clay. Colored zones appear on the column (366). A displacement technique has been de-
52 R
ANALYTICAL CHEMISTRY
scribed in which the different zones are indicated by fluorescence (285). A column of cation exchange resin in the hydrogen form is used, with ammonium glycollate as the displacing solution. Divalent and trivalent metals form glycolate complexes, some of which fluoresce while some do not. The technique was applied to traces of cobalt, zinc, and copper in animal feed. Temperature effects on chromatographic separation are receiving more attention, both in the inorganic and organic fields. Separations of the alkali metals (112) and the lanthanides (64, 112, 308) can be improved by proper temperature control. Organic compounds sometimes decompose or hydrolyze if the temperature is raised; thus uronic acids decompose above 60” C and aldonic acids epimerize (208). Even a t room temperature some reactions may occur; on the column, thus, lactose isomerizes to lactulose and maltose and cellubiose hydrolyze to monosaccharides during chromatography on a borate-loaded anion exchange resin. These effects do not occur a t 4” C (81). NEW EXCHANGE MATERIALS
Inorganic. It is well known t h a t i t is difficult to prepare zirconium phosphate exchangers in a reproducible manner. T h e only truly reproducible form is crystalline Zr(HP04)2.HzO, and this has poor ion exchanging qualities ( 5 ) . The good ion exchangers are amorphous, and the degree of crystallinity is hard to control. The water content of zirconium phosphate gels and their absorptive properties for cesium and sodium ions were studied by Albertsson (12), and it was shown that the high selectivity for cesium over sodium is found only with the amorphous material in solutions of low pH. The crystalline material absorbs only minor amounts of cesium and sodium ions below p H 3, and the selectivity depends on the loading; at p H 4-5, if the alkalimetal loading exceeds 0.05 meq/gram, sodium is preferred over cesium. Alberti and coworkers (8, 11) have studied exchange rates and ewhange distributions in titanium and zirconium phosphates and have shown the effect of drying temperature, water content, and degree of crystallinity. Zirconium arsenate (348) likewise shows the effect of crystallinity on ion exchange properties and shows a very interesting effect of p H on the order of selectivity of the alkali metal ions. Four different selectivity orders were observed, cesium being preferred below p H 2.6 and sodium being preferred above p H 4.6. Because p H affects the ionic charge density, these results may be explainable by the theory of Eisenman (see his chapter, ref. 227). Nancollas (254) has measured anion exchange
equilibria on hydrous zirconium oxide. Crystalline titanium and zirconium phosphates have been used in thinlayer chromatography (9). Cerium (IV) phosphate has been prepared in a fibrous form, stable to 200” C, which can be fabricated into sheets suitable for paper chromatography (10). Selectivity orders for cerium(1V) phosphate depend on the loading and crystallinity (181). The use of inorganic exchangers to recover cesium from fission-product wastes has led to the development of many new and selective exchangers, many of which are of the hexacyanoferrate type. Silver hexacyanoferrate shows exceptionally good selectivity for cesium over rubidium and potassium ions in hydrochloric acid solutions ranging up to 10X (136). Ferrocyanide molybdate (24) and ferrocyanide tungstate (154) likewise are very selective for cesium ions. Vanadium ferrocyanide (195), titanium ferrocyanide (218), and potassium and ammonium hexacyanocobalt ferrate, also called ammonium cobalt ferrocyanide (46,271), have been prepared. The hexacyanocobalt ferrates have been used to absorb trace quantities of cesium-137 from milk, sea water, and urine; the radioactive cesium is counted directly on the column (46). Heteropoly acid salts are still being investigated; pyridine and &hydroxyquinoline germanomolybdates (66) have been used for thin-layer chromatography; ammonium and thallium salts of phosphomolybdic and phosphotungstic acids have been studied (196). All are selective for cesium and effective in separating rubidium and cesium from other ions. Other inorganic exchangers include zirconium oxalate (231) and chromium tripolyphosphate (39), both selective for cesium ions; antimonic acid ( 2 ) , which s h o w a n affinity sequence S a > R b > Cs > K > Li in dilute nitric acid and N a > Cs > R b > K > Li in ammonium nitrate; manganese diovide (42) which is selective for manganese and chromium at the tracer level; silver chloride (122), used to absorb traces of iodirie-131; stannic phosphate, precipitated in the fibers of paper and used for thin-layer chromatography (281) ; and the crystalline zeolites, which can be used for column chromatography in molten salt mixtures (77, 7 8 ) . Different selectivity orders are observed in molten potassium nitrate and lithium nitrate, and a n explanation of this difference is suggested (77). The ion exchanging properties of silica gel have been studied (356) and techniques developed for absorbing silver, iron, and cobalt selectively from aqueous solutions with the aid of complex formers such as ammoiiin, ethylenediamine, and 1,lO-phenanthroline. Finally we note the possibility of loading inorganic exchangers with an-
ions or cations that are strong ouidizing or reducing agents (304), and using the products as oxidation-reduction exchangers. Resinous. Porous or “macroreticular” resins a r e being applied t o t h e analysis of petroleum products ( 3 5 8 ) . Acidic and basic constituents are absorbed by anion and cation exchange resins, respectively. Rates of sorption of aromatic amines by niacroreticular resins were measured in different solvents (275). A new approach to chromatography in nonpolar solvents is the use of oleophilic ion exchange polymers (526, 351); thus, a n anion exchange resin which w e l l s in benzene and benzene-methanol mixtures is made by reacting chloromethyl polystyrene with S,S‘-dimethyldodecylamine. The “standard” chelating resins with iminodiacetate groups on a polystyrene network are being used widely for the collection of traces of divalent and trivalent ions (144, 1 9 8 ) . Thus traces of copper, lead, zinc, cadmium, and nickel are recovered from large volumes of industrial waste water>, stripped from the resin by dilute nitric acid, and determined by atomic absorption spectrometry ( 4 2 ) . -1 very important paper by Ro..et (299) give. selectivity orders for the chelating resin Dowex -4-1 and s h o w that the distribution eoefficients for varioui divalent ions range over four or five power3 of ten, a much wider range than exists in sulfonic acid exchangers. I-raiiium(VI), mercury, aiid copper are held the most strongly, strontium, barium. and magnesium most neakly. Generally the Selectivity order parallels the order of stability of metal-EDTAi complese.. The nature of the binding betneen metal ions and chelating reyins has been studied (528);it seem.; that at low p H values calcium and magne>ium ion.; do not form chelate-, while nickel does. *it higher pH values (6 and more) calcium and magnesium do form chelates. Certain metal ions, including Cr(III), Hg(II), and P d ( I I ) , form “inert” complexes which exchange their ions qlowly a t room temperature but much faster a t 80” C (145). The complex with Fe(111) is very inert. Many new chelating and amphoteric (bifunctional) resins have been described. .1 re-in made from polyethyleiieimine and inonochloracetic acid was used to remove trace.; of calcium and magnesium ions from solution. of lithium fluoride used to prepare lithium fluoride crystals for phosphors (50). Starting with chloroniethylpolyatyrene one may add not only iminodiacetic acid, but sarcosine (144), S-methyl-pamiiiopropionic acid (144, 199, 201, 2029, and the nitrile of ethylenediamine tetrapropionic acid (200). Selectivity orders for metal ions on these resins are
described (144), as well as applications to the chromatography of metal ions (202) and amino acids ( 1 9 9 ) . Resins with guanidine and SUIfoguaiiidine functional groups have been prepared ( 1 9 4 ) ; they are very selective for the noble metals, gold, platinum, palladium, and the other “platinum metals” which form square planar complexes with d8 electronic configurations. Metals that cannot form this configuration are absorbed very weakly. Resins based on 8-hydroxyquinoline (37) have been used to separate fission products; a condensation product of resacetophenonoxime (342) is very selective for aluminum and copper; resins with interpenetrating networks made by polymerizing vinplpyridine in Doa ex50 (278) are used to separate platinum and palladium. The thermodynamic properties of a sulfonated copolymer of p-vinylanisol and divinylbenzene are described (364); this is a weaker acid than sulfonated styrene-divinylbenzeiie copolymer. Selectivity orders in phosphonic acid polymers of various types have been described (226, 245). -4s one would expect, thorium, uranium, and iron are held very strongly (226) and sodium is preferred over potassium (245). =in exchanger prepared from carboxymethylcellulose and dithizone has the same ielectivity pattern as dithizone ( 2 9 ) and can be used to recover traces of zinc, lead, copper, and silver from sea water. I t may also be used in fheet form for spot test.. l n o t h e r exchanger of fibrous structure, potentially useful in paper and thin-layer chromatography, is made from ethylenediamine, diethylenetriamine, and their homologs by reaction with a vinyl chloride-acrylonitrile copolymer (115). Cellulosic. Chapters on cellulose exchangers appear in Volumes 4 a n d 5 of (233). I n the two years under review, the use of different types of cellulose exchangers for inorganic ion exchange chromatography ha. been studied, particularly by Muzzarelli (247, 248, 250, 261), who ha- used many aqueous-nonaqueoui solvent mixtures. H e points out that there is a “physical” absorption of metals, independent of ionic functional groups, which is rapid and common to all types of cellulose. L-ndoubtedly this affects the movement of ions on resin-loaded papers (Gee below). Compared to zinc and cadmium, mercury is very weakly absorbed by cellulo-e phosphate exchangers, and nanogram amounts of zinc and cadmium can be separated from gram quantities of mercury using ether as a solvent (248). Other workers have used cellulose exchangers in columns to separate rhenium, molybdenum, and tungsten (158). Of course cellulose exchangers (87, 147) and exchangers derived from
dextran (383) find frequent application in the chromatography of organic acids and bases, peptides ( 1 4 3 , and proteins (87)* Liquid Ion Exchangers. These compounds a r e oil-soluble acids, bases, or salts a n d are normally used in solv e n t extraction. T h e y m a y be used as stationary phases in ion exchange chromatography if they are supported on a porous solid. Absorbent supports like silica gel or kieselguhr may be used, but porous fluorocarbon granules are better. As a cation exchanger, di-(2-ethylhexyl)phosphoric acid is the most used. This material strongly absorbs uranium and plutonium (152) and gives a n excellent chromatographic separation of calcium and strontium (219) using nitric acid solutions as eluents. Also with nitric acid, divalent ions are separated from the lanthanides and uranium ( 3 4 5 ) . This liquid ion exchanger is used in thin-layer chromatography with a suitable carrier to separate lanthanides (149, 278) and other inorganic ions. I t can also be supported on Whatman No. 1 paper, and Cerrai (82) has studied the migration of 67 cations in hydrochloric acid solutions with di- (2-ethylhesyl) phosphoric acid on paper a. the stationary phase. Thorium and scandium have been qeparated (35Q). Quinoline, its homologs, and alkaloids have been separated by chromatography on paper impregnated with this liquid (328). Liquid anion exchangers are primary, secondary, tertiary, or quaternary amines, and a comparison of different types supported on silica gel in thinlayer chromatography was made by Brinknian (54-57). H e also showed that cobalt, copper, and iron exist in these exchangers as the complexes C O C I ~ ~CuC142-, -, FeC14-. Metals have been separated by column chromatography with these materials as ftatioriary phases (11 9 , 1 5 1 , 2 5 5 , 2 7 4 , 5 0 5 ) ,and also by paper chromatography (282). PAPER A N D THIN-LAYER CHROMATOGRAPHY
We noted in the 1966 review [ref, ( 1 9 9 ) , 19661 that Chromatography in ion exchange re-in-impregnated papers can give results in harmony with column chromatography if certain precautions are taken. An important detail i-; to allow the solvent front to migrate part way up the paper, then place the sample spot behind the front. Then distribution coefficients can be calculated from migration ratios (Rp values) aiid vice versa (218). Severtheleqs certain anomalies remain, and it seems that the cellulose fibers do affect the migration of certain ions (file), including tin and copper, which attach themqelves to the paper and remain near the origin during development. VOL. 40, NO. 5, APRIL 1968
53 R
A comprehensive review of the migration of metal ions in resin-impregnated papers is given by Sherma ( S I S ) , who used nitric and hydrochloric acids in aqueous-nonaqueous solvent mixtures. H e reported some interesting separations: for example, on cation exchange resin paper, iron, cobalt, and nickel were nicely separated by 0.6N hydrochloric acid in 90% acetone; with 0.6N nitric acid in 90% tetrahydrofurane, gold migrated near to the solvent front, uranium(V1) had RF = 0.13, while other elements hardly moved at all. H e has also used resin papers impregnated with phenylbenzohydroxamic acid, and found ways to separate arsenic, cadmium, and mercury from other elements (312). I n another report Sherma (31%) compared resinimpregnated papers with modified celluloses containing sulfonic acid and quaternary ammonium groups, using aqueous-nonaqueous solvent mixtures and eight metal ions. Migration rates in aqueous thiocyanic acid have been measured (25, 38); the different oxidation states of plutonium (264) and technetium (321) have been separated on resin-impregnated and modified cellulose papers.
The use of paper impregnated with stannic phosphate was noted (287); a comprehensive account of the behavior of over 40 metal ions on stannic phosphate and tungstate papers, with over 40 solvent systems, is given by the same authors (286). Gold, antimony, and palladium could be separated from 39 other metal ions on stannic phosphate paper, using butanol-hydrochloric acid and butanol-nitric acid solvents. Zirconium phosphate-impregnated paper was compared with cellulose phosphate for paper chromatography in perchloric acid solutions (214). Resin-loaded papers are used to separate purines and pyrimidines (58),urina r y amines (335), and various organic acids (370). Paper-like sheets, made from polyethyleneimine and cellulose and supported on plastic, are used for thin-layer chromatography (288). Ion exchanging celluloses mounted on a n ultraviolet-transmitting glass are used for the chromatography of nucleotides (19).
Ion exchange resins, conventional and chelating, and hydrous zirconium oxide are mixed with cellulose as a binder and spread on thinlayer plates for the chromatography of
Table 1.
inorganic ions (34, 311). Thin-layer chromatography on strontium sulfate powder separates strontium-90 from yttrium-90 (206). On silica gel, a great many complexes of cobalt(II1) can be separated using a dimethylsulfoxide-methanol-perchloric acid solvent (109). The migration rate is determined primarily by the charge, since the silica gel acts as a cation exchanger. Trans isomers always migrate faster than cis isomers. Thin-layer chromatography on salts of heteropolyacids was noted above (66). CHROMATOGRAPHY OF INORGANIC IONS
Table I summarizes the chromatographic separations that have been reviewed. Certain aspects of these separations will now be discussed. Study of Complex Ions. Ions which form a n d decompose slowly, t h e socalled "kinetically stable" or "inert" complexes, can be separated from one another b y ion exchange chromatography, taking advantage primarily of differences in charge. T h u s reaction mixtures can be analyzed, individual complexes can be isolated, and conclusions can be drawn about reaction mechanisms.
Inorganic Applications
The order of elements is based on the periodic table, with the actinides last. Abbreviations: A, anion exchanger; C, cation exchanger; I, inorganic; P, paper chromatography; T, thin layer; Liq., liquid ion exchanger. Elements Separated from Exchanger Eluent Notes Ref. HC1 ( 256 1 Alkali metals Each other c, I. Antimonic "03 Na eluted'last (9) Li cs
cu
cu Ag Au
Ca Ca, Sr
Ba Ra
c acid
Na, K, Ca, M g Sea water Rb, etc.
C I
Milk, water Fission products K, Ba, etc. Other elements Water Plant products Rocks Solder Cd. Pb. Zn. etc. SIany elements Other elements
I IT C Chel. Chel. A A A C C CP
Other elements A1 Ca, Sr Ca, etc. Hard water Each other and Ba Sea water Conc. LiCl Si-, Ba Rb, Ba Sea water Urine Y. etc. Ferrites Th, Pa, U, Fe
IP A, c Chel. A C C C C A C
c C c, IC
C A C C A
CHaOII-HCl HC1 Various NHaNOa
From salt water
...
...
(292)
(353)
(24, 136, 196,
'3'Cs
On germanomolybdate
...
HC1
A1 also abs. Pb, Zn, etc., abs. Co, Fe, Zn also det.
HNO, HC1 HC1 HC1 NanSZOs
Cu, Pb, Sn'retained Cu passes
"03
HNO. HCl
... ...
...
HF (NH&SOI Acetate
...
Complexing NHhC1 HC1 HNOa Lactate EDTA HC1 Lactate HC1 Oxalate
I n tetrahydrbfuran I n butanol .. Pt metals also abs.
( 286 ) (31)
... ...
I n saline water I n limestones
... ...
. .. .. .
Radiochem. Radiochem. by Y
...
Ra passes
...
(Continued)
54 R
0
ANALYTICAL CHEMISTRY
Table I. Elements Zn
Cd
Separated from Cd, Cu, Pb Cd, Hg, In Cd, Cu Cd, Fe, U Soils, plants Zn Zn, much Hg Co, Zn, Xi, Cu Meteorites Sb, Sn '1, pl
B A1
sc Sc, La Lanthanides
U, much Zn Alk. metal salts Rocks Uranyl nitrate Fe, Ti Cu, Pb, Sn Other elements Rln Lanthanides, A1 Rocks Al, Ga, Fe, etc. Each other
Exchanger A A A IC A A C C A A C A A A A C A Chel. C C S A A A Liq. A C
C
Ga T1 Ti Ti, Zr Ti Zr Ge Sn Pb
P Phosphites, phosphates Phosphates, thiophosphite Nb Nb, Ta As Sb Bi
Sulfate Polysulfides Cr Cr M O
(Continued)
Eluent HCl HC1 HC1 NHaCl KCl KI Ether-HC1 Glycolate Thiourea "08
HClO4 Thiourea HC1
...
HC1 HC1 EtOH-HCl
...
HC1 ( "&SO4 HCI HCl aa. MeOH xH4scx Acetone-"08 Hydroxyisobutyric acid EDTA-lactate EDTA, HEDTA
Other elements Other elements Transition elements Various Fe, W, Mo, N b
C C C C C A
Two-phase HC1
Uranium alloys AI Th Hf, other elements B As, Fe, etc. Glasses Mn, Fe, Co, etc. Cu, Zn Bi Bi, T1, etc. Many elements Many elements Manv elements Silicate Phosphate from each other
A A A A A A A C A C C A A Chel. A A
HzOz
Sulfosalicilic Complexing HF-HC1
...
HCl His04 HoAc HoAc-HC1 HF HCl EDTA XaNOt HCl Various Hz0
Ref.
Notes I n minerals Butanol solvent
.. Cellulose exchgr. Displacement
...
In meteorites
HF elutes'ii hlannitol complex Nannitol complex Mannitol complex Fe, Ti complexed A1 passes A1 held Sc passes Sc passes Sc passes Sc passes Lighter elements sep. Heavier elements sep.
... ...
iiisi
i ,936i
i123,' 237) (151) (15)
(127, 229) (298, 308, 363)
(61)
(64, 280, %S%,
"Extractive ion exchg." Ga passes T1 eluted last
... ...
Elution order Fe, Ti, W, S b Zr eluted fikt Hf eluted first Ge passes Ge passes Sn absorbed Sn passes Sn absorbed P b retained Pb passes
(40) (118, 172, 337) (297, 539) (202)
..
P b passes I n fertilizer
(2951
A
Bauxite Th, other elements Each other Cu Ge, other elements Sb, Sn, Hg sn; CU As, Sn, Hg Sea water Pb, other elements Pb, Cd, Zn, Cu U, many elements Phosphate Rocks Limestones Other elements Mo, W Other elements W, other elements U
..
A
SHdC1
A C A Cell A A A A A Chel. A C A A A C Chel. A A C C
NaHS04 H~S04-Hz02 HCl. KCl Varibus Ho Ac-HC1 HCl HzS04 HCl-NHIF HC1 ~-~ HzS04 HC1, HNOi "03-THF HC1 Acetate
...
HF HiSOd-HF HBr "08-THF
Nb retained Nb passes
...
Other elements retained As passes Sb passes Sb passes Bi retained Bi passes Bi eluted last U and Bi pass Sulfate passes first Several methods Activation anal. Cr anion passes Cr bound strongest Cr eluted first W eluted before Rlo 310 eluted before U (Continued) ~ _ _ _ _ _
VOL. 40, NO. 5, APRIL 1968
55 R
Elements &lo,
W
w
Se, Te Te Mn Re
Separated from Other elements Steels Steels Each other, As Each other As, Sn, Fe, Zn U, other elements n1o hIo hIo, Other elements Silicate Each other
w
F Halides I
Os, sea water Milk 1 from 1 0 3 Other elements
Fe
Co, Ni Co, Ni co Ru
os
Pt, Pd Platinum metals
Th
Fe(I1) and Fe(II1) Other elements Fe, each other Each other Each other Cu, Ti Other elements Various complexes Sea water Each other Other elements Fission products Biological samples Uranium ores hIany elements, Zr Many elements Lanthanides, other elements illany elements, U Many elements, U Water, etc.
U
Pu Transplutonium elements
Many elements, Bi RIany elements Pu Soil, etc Fission products Am, lanthanides
Table I. (Continued) Exchanger Eluent A HzOt-HF C NaOH A, Liq. HCl-HF A HC1 HBr C A HF
A A A Cell A A A AI C AgCl A c, A C Chel. A C A C C A A, c Chel. A, C Chel.
2c
HC1 "03-THF HzS04 NH!C?;S Various Acetate NaN03 NaN03 * .
Clz-Hz0 Various
..
... HC1, HZij'd4 Complexing RIalonate Polyphosphate HCl "03
NaOH Various
... ..
Se eluted before Te Te retained, eluted by oxalic acid Mn passes hIo passes, Re absorbed Re absorbed Re absorbed'
...
... I retained' ' ' Radiochemical
...
*..
Fe strongly ibs. Mixed solvents Thin column Co absorbed Ti passes Acetone-HZ0 Catalytic hit. Pd eluted by thiourea
...
Products sep.
...
A A C A A A, Liq. C C A C A A C A A A
Sotes No, W pass W passes 'N passes Se, As eluted first
Activation Th passes Th retained Th passes Aq. acetone; Th retained
HNO~-THF HC1 HCl, HSOI EDTA HC1, IIIL'OI HYOq EDTA, "03
Phosphon;c' exchgr. Cellulose phosphate Selective ads U passes U passes I . .
P u retained
Pu, Th reiained
...
Reference (338)describes the anion exchange behavior of 52 elements in sulfuric acid solutions. Other references referring to a large number of elements are (93, 94, 140, 157, 191, 192, 257, 286, 299, 313).
The complexes Cr(OH2)&12+ and Cr(OH2)J2+ are prepared by the oxidation of chromium(I1) solutions and are always accompanied by Cr(OH+j3+. Cation exchangers absorb the triplycharged aquo-complex in preference to the doubly-charged complexes and a separation is easily made (241, 341). The products of hydrolysis of cobalt(II1) diethylenediamine diacetatoperchlorate can be separated according to charge type (80), as can the decomposition products of peroxochromic acid (17, ,243). A new binuclear complex ion was discovered in this reaction (17). The mechanism of hydrolysis of C O ( N H ~ ) ~ X*+,where X is a halide or nitrate, was studied by measuring the ratios of singly and doubly charged ions produced (67). T h e complexes CrenzF2+(red) and Cren-
56 R
ANALYTICAL CHEMISTRY
Fa- (blue) are readily separated by ion held within a n ion exchange resin has been the subject of much study, and exchange (354). Other studies of cobalt (221) and ruthenium (242) coma spectroscopic investigation (88),indicates that in a n anion exchange resin plexes are cited. cobalt chloride is bound a. CoC142-. The separation of cis- and transCo(II1) complexes by thin-layer ion To illustrate the use of ion exchange exchange chromatography on silica gel to study the course of chemical reactions was cited (109). The optical isomers of one may cite the chromatographic sepa trinuclear cobalt(II1) complex were aration of the hydrolysis products of separated by chromatography on a P2C1d and P214(361), P4S, (276), and column of cation exchanging cellulose PoC13 (277). One of the products (59), and the optical isomers of C ~ e i i ~ ~ from + the phosphorus sulfides was the previously unknown compound, amwere separated on a n anion exchange resin carrying optically active antimonium monothiophosphite, ("&monyl tartrate ions as counterions HPOZS. (368). This method of resolving optical Collection of Trace Impurities. isomers by passage through a resin with a Some of these applications have alweakly held optically active counterion ready been cited (see t h e discussion of seems to be of general application (368). chelating resins). A common techThe nature of complex ions that are nique is t o absorb t h e trace impurities
selectively on disks of resin-impregnated paper and then determine the amounts by X-ray fluorescence qpectronietry (35, 36, ?9,83, 97‘,98, 142,143) or by atomic absorption for the lighter elements (98). Materials n hose trace impurities have been concentrated in this way include aluminum (98),iron and steel (97), petroleum (36),phthalic acid (36), hydrofluoric acid (829, molybdenum (330), and plutonium (143). Absorption of the major constituent is avoided in a number of ways; for example, molybdenum is anioiiic in dilute hydrochloric acid and is not retained by a cation exchange resin. Selective absorbents can be used; traces of uranium are absorbed from water by cellulose phosphate paper (GO), and the use of dithizone-cellulose wit3 mentioned earlier (29). Trace impuritieh in gallium were separated by ion exchange (322). -1mixed-bed slurry method was used to extract tracer of fission products from water (117‘); the technique is faster and simpler than column chromatography. Special techniques are de+cribed for the recovery of lithium (292, 353), boron (365), iodine (309), aiid uranium (143) from sea water. Activation Analysis. T h e prediction in t h e 1966 revieir t h a t high-resolution gamma-ray spectrometers vc.ould decrease t h e need for chemical separations in neutron activation aiialysis does not seen1 t o h a v e been fulfilled. Separations b y ion exchange have followed activation in the analysis of rocks (62, 6S, 159, 349) and meteorites (116, 174, 311). Trace elements thus determiiied include chroniium (6d), copper, gallium and zinc (&?), rhenium (159), antimony and tin (174) and niercury (116,174). Activatioii can be used to measure ibotopic abundances; thus calcium-48 011 activation yields 49Ca which decays to 49Sc and 49Ti,which in turn may be separated by ion exchange
(89). Trace of cesium iii salt minerals have been determined by activation (332), a5 have trace elements left by insecticide and fungicide sprays on vine leaves (128). Uranium concentrates have beeii analyzed ( I ) , aiid a number of papers report the determination of trace coiitaminaiits in high purity materials, such as single crystals of alkali halide$ (134). Here, calcium, strontium, barium, aud scandium ions were absorbed by a resin before activation, as it was important to remove as much sodium as posbible before irradiation. Arsenic, tellurium, arid tin mere determined in metallic iron using solvent extraction as well as ion exchange to separate the products. Impurities in gallium (20), aluminum (118, 17’6, 235), lead (118), thallium (281) were determined, and activation was used to identify and measure the impurities in
zinc sulfate solution that interfered with the electrodeposition of zinc (92); these impurities included mercury, rare earths, aiid uranium. Sodium and potassium traces were determined in molybdenum and tungsten (lO4), tungsten aiid cobalt in stainless steel (119). These analyses presented the problem of high matrix activity, which made chemical separations essential before gammaray spectrometry. Ai ingenious technique for getting rid of matrix activities in activation analysis is “isotopic ion exchange” (343). Suppose that a matrix element like barium has a high affinity for a resin; the solution after activation nould be passed through a column of resin loaded with inactive barium. Active barium would replace inactive barium in the resin, while weakly absorbed constituents would pass through the bed and nould be freed from the radioactive matrix. -1 modification of the technique permits the absorption of n eakly absorbed radioactive ions and their substitution by inactive isotopes. Aqueous-Organic Solvents. The use of solvent mixtures in t h e separation of metals h a s become so commonplace t h a t i t is clifficult t o identify all t h e references. Generally speaking, oxygen-containing, donor solvents are used, like acetone, tetrahydrofuran, a n d t h e lower alcohols a n d glycols; they are mixed with 10% to 50y0 of water. Such solvent mixtures have a lower dielectric constant than water, so that the formation of ion pairs and clu.ters is favored. Complexes like CoC142- and KiCld2- are stabilized, and so are aggregate3 with zero net charge, like H+FeC14- and U022+(K03)2-. This means that the absorption of some metals on anion and cation exchange reziris is increased, \r hile the absorption of others is decreased or prevented altogether. These effects can be produced at low acid concentrations, and the solutions recovered from the column are easily evaporated and prepared for further aiialysis. The anion exchange separation of iron(III), cobalt and nickel in 80% acetone-20yo 6111 HCl makes a n excellent student experiment or rapid demonqtration. Iron f l o w through the column without retention, and afterwards nickel and cobalt can be eluted in this order by adding water to the eluent. T h e behavior contrasts strongly with that in simple aqueous solutions, aiid, of course, the method is eminently suitable for separating small amounts of cobalt, nickel, and other divalent ions froin large amounts of iron. The behavior of iron and uranium just cited resembles t h a t seen in extraction b y oxygen-containing solvents like ethers, ketones, and esters, and for this reason the technique has been called “combined ion exchange and
solvent extraction.” I t was reviewed by Korkisch in ref. (334). Korkisch and his group have done more than anyone else to exploit this technique. References (90, 182-184, 191) are sunimaries discuqsing many elements and solvent combinations, including mixtures with tertiary amines (90). The separation of large amourits of iron and uranium from minor amounts of other elements is described (188). Uranium is relatively M eakly absorbed from tetrahydrofuran-nitric acid solutions by cation exchange reqiiis, bo small amounts of accompanying elements Cali be separated from large amounts of uranium (184, 186, 191). On the other hand, anion exchange resiris absorb uranium strongly and selectively from glycolhydrochloric acid solutions, and traces of uranium can be recovered from sea water and marine sediments (143). The separation of iron (187) and uranium (185) is discussed in detail in other papers, arid ion exchange i-. compared with conventional solvent extraction (185). Other workers describe separations of lanthaiiides in aqueous alcohols (123, 237) and acetic acid (204); of scandium (32) and halide ions (246) in aqueous acetone; and of titanium ( I S ) , zinc, cadmium, and mercury (139). Iron, cobalt, and nickel are >eparated by anion exchange in aqueous-alcoholic sulfuric acid (209). Ion exchange in liquid ammonia has beeii +tudied by Phipps and Hunie (2?2), and reference has already been made to solutions in fused salts (7, 77,
78). ORGANIC COMPOUNDS
The separations of organic compounds are summarized in Table 11. Certain classes of compounds and types of separation are discussed below. Carboxylic Acids. Differential complexing has been used t o separate metal ions; now it is used t o separate dicarboxylic a n d hydroxy acids. T h e y are eluted from a n anion exchange resin column by solution of magnesium acetate (211) or zinc acetate (207). Elution by sodium acetate solutions has been studied a t different temperatures (162, 208) and, as noted above, it was found that aldonic and uronic acids suffer decomposition above 60” C. Nitric acid eluent wa. uied for tartaric, lactic, oxalic, arid acetic acids (216). Vsing nonaqueous solvent mixtures, organic acids have been separated by elution from a cation exchange resin (307). Paper chromatography (370) and column chromatography with acidbase indicators (114) have also been used. Carbohydrates a n d Their Derivatives. T h e y are separated b y anion exchange as borate complexes (137, 171, VOL. 40, NO. 5, APRIL 1968
57 R
259, 357). As noted above, caution is needed because certain disaccharides hydrolyze on borate columns a t a n appreciable rate a t room temperature (81).
Using 90-95Oj, ethanol as eluent, sugars and sugar alcohols were separated by chromatography on cation exchange resins; the effect of the alkali
Table It. Organic and Biochemical Applications (Abbreviations as in Table I : L = ligand exchange) Compounds Exchanger Eluent, method, notes Acids Aldonic Aromatic Carboxylic
Chloroacetic Chlorobenzoic Saphthenic, salicylic Unsaturated Uronic Alcohols Polyhydric, glycols Sugar alcohols Alkaloids Amines Aliphatic, alkanolamines Aliahatic. various Aromatic Aromatic, p-nitroaniline Diamines Ethanolamines Hexosamine Hydrazines Phenolic amines tJrinary Amino acids
A A
C A A A A C A C CL L A
Acetone-CH&-HsO In herbicides Salting-out chrom. In petroleiim products Cis-trans; incl. esters Bcetate buffer
C A A CP
Cationic forms studied Borate eluent R a t e r eluent Also quinoline bases
IC CL C C CL C A CL C C C
HC1, zirconium phosphate, 80" C Aqiieous ammonia Sublimation chromatography Rates stiidied Petroleum products Citrate, borate Aqueous ammonia Aqueous ammonia, 60" C Alcoholic ammonia Di- and polyamines
C
Includes aromatic type Rapid, automatic
A A
CL CL Basic n'-met hylamino Sulfrir-containing Tyrosine, phenylalanine Anionic detergents Anthocyanin; Antihistamines Carbohydrat ea
CL C C A
E,
A IL C A A A Disaccharides A Moiiosaccharides A C C Coumarins C Glutamine A Lignin sulfonates CL Xitro compounds Kucleotides and nucleosides C CL A T A Sucleic acids L Olefins C Peptides CL A Phosphates, organic Phthaleins Special Polyelectrolytes AC Proteins C Purines, pyrimidines C CL Special Sulfonic acids, aromatic
Sulfoxides, dimethyl Aliphatic
58 R
Acetate buffer lllethanolic NaCl Water Zn, Llg acetates Na acetate Kitric acid
C C
ANALYTICAL CHEMISTRY
...
...
Automatic; Cd resin From, sea water; Cu-chelating resin Sepd. from peptides Aqiieoua ammonia Automatic Automatic
...
lIacroretic\ilar resin On A1,03 or alumina-silica gel hIethanolic HC1 Borate buffer Borate; incl. hemicelluloses Borate; hydrolysis noted Borate (incl. disaccharides) Sulfate; dextran exchanger Aq. ethanol, 75-100" C 105% methanol, acidic Degradation noted Ideiitificat ion Clathrates formed on column Rapid sepn. Cu-chelating; bases included Pellicular ion exchange resin DEAE-cellulose Ribonucleic acids Al2O3-.4gXO3; pentane eluent Cellulose exchanger Sepd. from amino acids Bisulfite; sepd. from inorganic P Ion exclusion removed salt Test of theory Cellulose exchanger A P also used Aq. ammonia eluent Sephadex; naphthalene sulfonates sepd. Sepd. from amino acids From petroleum products; methanol elution
Ref. (208,303) (75)
i350 i
boj
( 3581 (111, 306) (162, 208, 305)
metal counter ion was studied (91, 163). They can also be separated on anion exchange resins in the sulfate form (164). Sugar alcohols are separated by water elution on a strong-base resin in the hydroxide form (365),or by elution with concentrated borate buffers at closely controlled temperature (331). Amino Acids. Improvements in t h e standard cation exchange technique continue t o be made, gaining speed a n d resolution using uniform, smalldiameter resin beads a n d well controlled pumping systems (238, 316). M a n y applications to specific clinical and biochemical problems are reported (101,102,113, 803,250,329, 340). The migration of isotopically labeled acids has been found to differ from that of the normal forms (176). Demonstrating the sensitivity of commercial amino acid analyzers, Oro and Skewes (263) determined the amino acids released by dipping human fingertips into a citrate buffer, and pointed to fingerprints as a source of contamination in experimental work. Reports of finding amino acids in meteorites were found to be mistaken. Ligand Exchange. This relatively new technique is finding more applications, a n d as noted in t h e introduction t o this review, it is now used in a commercial amino acid analyzer. T h e stationary phase is a cation exchange resin loaded with cadmium or zinc ions, a n d t h e eluent is aqueous ammonia. The amino acids form coordination complexes with the metal ions and so does ammonia. T h e ammonia displaces the amino acids as ligands to the metal ions and forces them down the column. A difficulty in applying ligand exchange to amino acids i- that the metal ions are removed from the resin also, as uncharged or singly positive complexes are formed. Arikawa and Makinlo (18) overcame this difficulty by adding metal salt in carefully regulated concentration to the eluting solution. The metal ions are less easily displaced if they are incorporated into a chelating resin, though their capacity for coordinating ligands is thereby decreased (319). Copper-loaded chelating resins have been used to separate peptides from amino acids in urine (68), to concentrate the amino acids in sea water (324), and to separate nucleosides and nucleic acid baqes (155). Nickel-loaded sulfonic acid resins are generally the most satisfactory for separating amines, including isomeric primary amines, diamines, alkanolamines, substituted hydrazines, and ethyleneimines (319). Ammonia is usually used as the eluent, though borate buffers have also been used (68). h more complex phenomenon which is probably a type of ligand exchange is the separation of isomeric nitroethylbenzenes on a column of nickel picoline
thiocyanate, eluting with a solution of amnioiiiuin thiocyanate and y-picoline (170). T h e use of potassium platinum(11) chloride for the chromatography of olefiiis, and of chloride complexes of mercury(I1) and thalliuni(II1) for the chromatography of halide ions is also noted (45). Macroreticular resins carrying copper, nickel, and iron(II1) counterioiis have been used t o absorb acidic a n d basic additives from petroleum products (358). Metal phthalocyanines dispersed in silicone oil have been used as stationary phases in gas chromatography (270); the metal atoms bind oxygen- a n d nitrogen-containing ligands, and these materials should be applicable to liquid chromatography too. Ligand-exchange chromatography of oxygen-contaillingitaiiiiiig substances is illustrated by the separation of anthocyanines (which form complexes with aluminum ions) on columns of aluminum oxide, using acidic methanol as eluent (48). Alumina and silica gel impregnated with silver nitrate continue to be used for the chromatography of olefins (84) and unsaturated acids ( 1 2 2 ) . Cis and trans isomers are separated. -1macroreticular resin containing silver ions has also been used t o isolate esters of uiisaturated acids (806). ACKNOWLEDGMENT
Thanks are expressed to the U. S. Atomic Eiiergy Commission, Contract dT(ll-1)499, for its assistance in preparing this and earlier reviews. LITERATURE CITED
(1) .4bdel-ltassoul, .4.A., Wahba, S. S., Abdelaziz, A., Talanla 13, 381 (1966). (2) Abe, l l . , Ito, T., Bull. Chem. SOC. J a p a n 40, 1013 (1967). (3) Abrao, A., Conf. Interam. Radioquim., i s t Jfontcvideo, 1963, p. SO. (4) Ahlgren, P., IIartler, N.,Svensk Kern. S'idskr. 78,404 (1966). ( 5 ) Ahrlaiid, S., Albertsson, J., Aluas, A , , Ilemmiiigsson, S., Kuhlberg, L., Acta Chem. Scand. 21, 195 (1967). (6) Aksehod, T. I)., Fodor, I. I., Baeu, A. A., Dokl. d k a d . ,Yauk SSSR 174, 707 (1!167). ( 7 ) Alberti, G., Allulli, S., Conte, A., J . Chromatog. 24, 148 (1966). (8) Alberti, G., Cardini-Galli, P., Constantino, y., Torraca, E., J . Inorg. .Yucl. Chcm. 29, 571 (1967). (9) Alberti, G., Giainmari, G., GrazziniStrazza, G., J . Chroniatog. 28, 118 (1967). (10) Alherti, G., hlassucci, 31. A,, Torraca, E., Ibid., 30,579 (1967). ( I I ) Alherti, G., Torraca, E., Conte, A., J . Inorg. S u c l . Chern. 28, 607 (1966). (12) Albertsson, J., Acta Chem. Scand. 2 0 , 1689 (1!)66). (13) Alimnrin, I. P., Brykina, G. D., Belyavskaya, T. A , , Vestn. M o s k . Uniu., Ser. I I , K h i m . 21,76 (1966). (14) Alimarin, I. P., Nedvedeva, A. %I., Zh. Analit. Khim. 22, 436 (1967). (13) Alstad, J. Brunfeldt, A. O., Anal. Chim. d c t a 38, 185 (1967). (16) Araki, S.,Bunseki Kagaku 14, 1163 (1965).
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~
Granatelli, L., CHEM.39, 1238 (1967). 135) Ibid.. D. 1331. (37) Ber&ard, H., Grass, F., Jlikrochim. Acta 1966, p. 426. (38) Bertazzi, S . , Barbieri, I%., Rizzardi, G., J . Chromatog. 30, 640 (1967). (39) Betteridge, I)., Stradling, G. N., J . Inorg. .Yucl. Chtm. 29, 2652 (1967). (40) Bhatnagar, 11. P., Trivedi, 13. G., Indian J . Chem. 5, 166 (1967). (41) Biechler, D. G., ANAL. CHEW 37, 1054 (1'365). (42) Bigliocca, C., Girardi, G., Pauly, J., Sabbioui, E., IIelloni, S., Provasoli, A , , Ibid. 39, 1634 (1967). (43) Birkhoper, L., Kaiser, C., Donike, AI., J . Chromatog. 22, 303 (1966). (44) Blattner, F. li., Erirkson, H. P., Anal. Biochem. 18,220 (1967). (45) Bock, It., RIorierjan, -4.,2. Anal. Chcn~.230. 1 11967). (46) Boni, A. L.,ANAL. CHEM.38, 89 (1966). (47) Borner, K., Z . Klin Chem. 4, 212 (1966); Chem. rlbstr. 65, 14081b. (48) de Bortoli, >I. C., ANAL. CHEW 39,375 (1967). (4i) Bosholm, J., Anal. Chim. Acta 34, I 1 (1966). (50) Bosholm, J., J . Chromatog. 21, 286 (1966). (51) Bottei, R. S., D'Alessio, A. S., Anal. Chim. Acta 37,405 (1967). (52) Bottei, R. S., Trusk, A, Ibzd., 37, 409 (1967). ( 5 3 ) Brendel, K., Roszel, N. O., Wheat, R. W.,Davidson, E. A , , Anal. Bzochem. 18, 147 (1967). (54) Brinkman, U. A. T., de Tries, G., van Dalen, E., J . Chromatog. 22, 407 (1966). ( 5 5 ) Brinkman, U. A . T., deVries, G., van Dalen, E., Ibid., 23, 287 (1966).
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e
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