Chapter 22 Inorganic compounds

Chapter 22

Inorganic compounds M. LEDERER

CONTENTS 22.1. 22.2. 22.3. 22.4. 22.5. 22.6. 22.7. 22.8. 22.9. 22.10. 22.1 1 . 22.12. 22.13.

Introduction ................................................. Reversible complex equilibria . . . . . Complexing equilibria that are not instantly reversible . . . . . . . . . . . . . . . . . . . . . . . . . . Hydrophobic adsorption and the “perchlorate effect” Ion-pair or outer-sphere complex for Ion chromatography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ........ High-performance liquid chromatography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gel chromatography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gas chromatography. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Resolution of optical isomers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Separation of coordination complexes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Scandium, yttrium, the earths, and actinium . . Condensed phosphates .................

........................................................

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

B459 B460 B467 B468 B469 B47 1 B473 B475 B478 B478 B480 B482 B485 B487 B488

22.1. INTRODUCTION The purpose of this chapter is to give a perspective of inorganic chromatography today. It is not intended as a complete survey of the field, which would require more space and would duplicate numerous recent monographs on the various branches of inorganic chromatography. Both chromatographic and electrophoretic techniques will be discussed, as they are often used together in the same investigation and are essential for a complete picture. Inorganic chromatography has two main purposes: (a) The isolation and/or determination of an element. Unlike organic chromatography, inorganic chromatography has a wide range of competing methods available for this purpose, such as polarography, atomic absorption spectrometry, spectrographic methods in general, and radioactivation techniques. Although many chromatographic methods were proposed earlier, very few of them have survived competition with other techniques, except for instances where their relative cheapness and the convenience in carrying out a large number of analyses is advantageous. (b) The separation and determination of ionic or molecular species in solution. I t is in this field that chromatography has fostered considerable advances in inorganic chemical research. Some fields were developed almost entirely by the application of chromatographic methods, such as the chemistry of polyphosphates and of astatine compounds and the solution chemistry of the platinum group metals. References on p. 8488

B460

INORGANIC COMPOUNDS

22.2. REVERSIBLE COMPLEX EQUILIBRIA The general idea of the solution chemistry of metal ions is usually based on elementary electrochemistry. which leaves most chemists with the impression that in the usual concentrations encountered in “wet analysis” the ions are essentially in the “free” form. For instance, an “ionic mobility” for the “Fe3’ ion obtained by conductivity measurements at infinite dilution is even quoted in textbooks on electrochemistry. Thus. let us take Fe’ as an example to illustrate the solution chemistry of metal ions. ( a ) When pink ferric nitrate hydrate is dissolved in distilled water, a pale-brown solution i> obtained. which contains members of the following hydrolysis species: ”

Fe(H,O):’ unstable

+

Fe( H 2 0 ) , 0 H ”

- Fe(H,O),(OH)l -Fe(OH)y

polymers

I n fresh solution>. the preponderant species is Fe(HzO),OH’ . Dirners between u r i o u s species art. also possible. linked by O H bridges. They. as well as the main >pecks. vary with the age, concentration, and temperature of the solution. These reactions are not entirely reversible. and some aged solutions or old samples of the d i d give a number of zones in various chromatographic systems. ( b ) When pink ferric nitrate is dissolved in HCI, a yellow to brown solution is obtained, containing mainly the following species: Fe( H,O)d. = FeCI’

’ G

FeCI’ = FeCI; = H FeC14

The neutral and the anionic species ( H - FeCI, seems to be a rather strong ion pair) are preponderant in ca. 6;V HCI. In none of the solutions can the Fe3+ (i.e. the Fe(H1O)i’ ion) be found to any extent. ’4sa simple example of a chromatographic separation of inorganic ions, let us consider the separation N i ” / F e ” . Ni” does not form complexes beyond possibly NiCI’ in HCI of a concentration of up to 12 N . F e 3 + , on the other hand, exists in HCI of a concentration of 6 N or above mainly as the ion pair H ’ FeCI, , which is strongly hydrophobic and behaves as an anion. Thus, as long as the concentration of HCI is above 6 N . it is possible to separate these two metals by virtually any chromatographic method, e.g.: ( a ) Solvent extraction with ether: Ni” . 0% extracted; F e 3 + ,99% extracted. ( b ) Anion-exchange chromatography on a Dowex-l column with 8 N HCI: F e 3 + . adsorbed as a brown band; N i * + ,eluted. (c) Partition chromatography on paper with 1-butanol-8 N HCI ( 1 : 1): N i l + , R , 0.36; Fe” , R,-0.98; the hydrophobic H’ FeCI, is well extracted into the butanol phase. Another separation, In” /Ga3 ?,/TI3*,is illustrated in Fig. 22.1. I t is obvious that TI3- and In3* can be separated by either partition chromatography or ion-exchange chromatography or even by solvent extraction at a wide range o f HCI concentrations. but Ga3+ will separate from In3+ only above 2-3 N HCI and from TI’- only below 5 N HCI.

REVERSIBLE COMPLEX EQUILIBRIA

B46 1

?

kl

40

5.m 0

2

4 6 8 1 0 1 2 M HCI cmcn

0

2

4 6 8 HCI concn

10

12M

0

0

1

2

3 4 5 HCI concn

6

7

8

M

Fig. 22.1. Dependence of the R , value in n-butanol (a), the ion-exchange equilibrium on Dowex 1 (b), and the partition equilibrium in ether/water (c) on the concentration of HCl in the solvent for TI3+,In3+, and Ga3+. (Reproduced from Metodi di Separazione nella Chimica Inorganica, Vol. 1, 1963, p. 199, with permission 1641.)

The chromatographic data for most metal ions (and for many other ions) are usually presented in the form of the periodic table. As shown for a few different systems in Figs. 22.2-22.5, the separations depend much more on the HCl concentration in the aqueous solution than on the chromatographic system. We can see here an important feature of inorganic chromatography: numerous metals form complexes with HCI at various HC1 concentrations, and this makes it possible to change the separation factors over a wide range and, as shown in Fig. 22.6, to elute metals by suitably varying the concentrations of HCI. In this kind of chromatography there is thus no need for a large number of theoretical plates. For most of the chromatographic work on anion exchange the columns were cut-off 10-ml pipettes with a plug of glass wool at the bottom to hold the resin. As many of the metal ion halide complexes are colored (e.g., those of Co, Cu, Fe), there is often no need for a fraction collector either, as one can collect each colored fraction in a separate beaker. On the other hand, a suitable combination of an efficient column with (in this case) suitable HCI concentrations and organic solvents permits the elution of a dozen heavy metals in a matter of approximately 30 min, as is shown, e.g., in Fig. 22.7. In summary, reversible complexes, especially those of the heavy metals, have been separated on cation exchangers, anion exchangers, liquid ion exchangers supported by cellulose or polymers, and by partition chromatography, reversed-phase chromatography (e.g., on acetylated cellulose) and by paper electrophoresis. The data on planar methods have been collected [ 1,2], and these collections make an excellent starting point for newcomers in the field.

References on p . B488

Fig. 22.2. Ion-exchange data for Dowex-1 with HCI. no ads.= no adsorption in 0.1-12 M HCI; sl. ads.= slight adsorption in 12 M HCI; str. ads.- strong adsorption; distribution coefficient, 0, 1. (From Proc. Inr. Conf Peaceful Uses A t . Energy, Geneuu, Vol. 7, 1955, as reproduced in ref. 65. with permission.)

U

5

C 0

wz

Fig. 22.3. R, values of ions in butanol-HC1 mixtures. All solvents were prepared by shaking equal volumes of aqueous acid and butanol; with 2 M HCI only one phase is formed. (From Anal. Chim. Acra, 16 (1957) 555, as reproduced in ref. 66, with permission.)

,

,I.

t

II

t , . . J

"

i .

A

D

J1 ,

0

I

1

0

,

I

ww

!

F ig 22 4 Chromatography on paper, treated with 0 1 M d1-(2-ethylhexyl)orthophosphon~ acid in cyclohexane Plot of R I. values of the elements as a function of the loganthm of the molarity of the solvent (HCI) (Reproduced from J Chromatogr, 24 (1966) 383. wlth permission [67] )

z

I

0

?5 P 20

0 0

5

0

C Z

F1

;a

m

<

m irr !2 W

r

m

8 5r m X

s5 t W E

>

Fig. 22.5. R values of metal ions in HCI on papers. impregnated with liquid ion exchangers. Paper: Whatman No. 1 . impregnated with a 0.I M solution of the exchanger in benzene: solvent: HCI: . Amberlite LA-2: - - tri-ti-octylamine. (From Chem. A I I (Wur.ww.). ~ 12 (1067) 1071. as reproduced in ref. 6X.. with permission.) ~

-.

INORGANIC COMPOUNDS

4CI

0 5MHC1

HCI

4 0005MHCl

4

Volume ( m l )

3

Fig. 22.6. Separation of transition elements Mn to Zn by ion-exchange chromatography. Column, 26 cmX0.29 cm', Dowex-I: flowrate. 0.5 cm/min. (From J. Amer. Chem. SOC., 75 (1953) 1460, as reproduced in ref. 69. with permission.)

hydr acid

(

hydrochlcric acid:

( p e r c e p t acerone:

5

15 20 Retention time ( m i n u t e s )

10

25

30

35

Fig. 22.7. Separation of metal ions on Amberlite 200 (25-30 pm). Column. 120 X 5 mm ID; flowrate. 22 cmjrnin: temperature. 40°C; column inlet pressure. 16-25 atm; color-forming reagent solution. 0.02% 4-(2-pyridyl~o)resorcinolin ammonia, concentration (a) 0.7 M and (b) 1.2 M sample volume, 60 ml. Amount of metal ( X 10- mole); Cd2', 9.6; Z n 2 + . 4.8; G a 3 + , 4.5; Pb2+. 12; C u 2 + , 4.8; Co2' , 7.2; Mn2'. 12: V4+, 57; N i 2 + , 12; A i 3 + , 9.6; Ca", 1.2.103; M g 2 ' , 6 . 1 0 2 . (Reproduced from J . C'hromatogr., 137 (1977) 381, with permission 1701.)

NOT INSTANTLY REVERSIBLE COMPLEXING EQUILIBRIA

8467

22.3. COMPLEXING EQUILIBRIA THAT ARE NOT INSTANTLY REVERSIBLE Looking at Figs. 22.2-22.5, one may think that the separation of any mixture of metal ions is merely a matter of selecting the optimum conditions for obtaining a difference in complexation and then applying them in the most suitable separation technique. However, there are a number of metal ions, notably Rh3+, Ru3+ and C r 3 + , that form complexes, but at rather slow rates, so that the variation of complexing concentrations usually yields a mixture of complexes. For example, RhCl2- in aqueous HCI will first hydrolyze quickly to Rh(H,O)Cl:- and then more slowly to form a mixture of chloro-aquo complexes, as is best illustrated in Figs. 22.8 and 22.9. Such metal ions, therefore, do not yield one band, but a number of bands in all chromatographic systems. Although many authors include such metal ions in the “periodic table” type of representation of the chromatographic data, this usually refers only to a predominant species, and application of the data will give erroneous results in most actual analytical separations. Special emphasis should be given here to Ru3+, which forms extremely stable nitrosyl and nitro- as well as nitrato-complexes. A solution of ruthenium in HNO, will always be a mixture of such complexes (sometimes also

Fig. 22.8. Dependence of the hydrolysis of rhodium on HCI concentration. Rhodium chloro complexes (0.1 N ) ; buffer, 0.3 N acetic acid-0.2N sodium acetate; paper, Schleicher & Schiill 2043 b mgl; electrophoresis for 30 min at 3 kV. (Reproduced from Chrornatogr. Rev., 6 (1964) 191, with permission [31.) References on p . 8488

B468

INORGANIC COMPOUNDS

Fig. 22.9. Electrophoretic separations of fresh and aged rhodium solutions. Khodium r.hloro complc.rc\ (0.1 N ) ; buffer. 0.3 N acetic acid-0.2 N sodium acetate; paper. Schleicher & Schiill 2043 h mgl: electrophoresis for 30 min at 3 kV. (Reproduced from Chromarogr. Reo., 6 (1964) 191. with permission [ 3 ] . )

containing polymeric species) in slow evolution. This is still one of the major problems in analyzing solutions of the common fission products. Chromatography and electrophoresis have for the first time permitted the separation of such mixtures and thus also the isolation of individual species as well as the calculation of complexing (stability) constants. An excellent review by Blasius and Preetz [ 3 ] indicates the possibilities of chromatographic and electrophoretic methods in this field.

22.4. HYDROPHOBIC ADSORPTION AND THE “PERCHLORATE EFFECT” A number of chloro-complexes of metal ions, especially those of the last line, viz. Au3-, Hg” . Po4’. but also Sb5-, Fe” , Ga7* , have extremely high K , values (order of 10‘) when chromatographed in HCI solutions on anion-exchange resins. They also move near the solvent front in partition chromatography with butanol-HC1 and are rather strongly adsorbed on neutral or sulfonic acid resins. Some are even adsorbed on cellulose paper from HCl. This is obviously not due to an “ionic attraction” between an anion such as AuCI, and an ionized substituted ammonium group of the resin, but has the character of a hydrophobic adsorption. On neutral supports, there is also increased adsorption by salting-out (usually with LiCl) and desorption with organic solvents. Typical results for cellulose paper are shown in Figs. 22.10a and b. These ions usually cannot be eluted from anion-exchange resins by HCl at any concentration, but they are rapidly eluted with HCIO,. This drastic desorption was first termed the “perchlorate effect”. However. it was shown later that not only perchlorate but also nitrate and other oxygenated anions may have the same effect, which is best explained by the competition of hydrophobic anions for the same adsorption site.

COMPLEX FORMATION

DWU7

10

08

06 Rf OL

02

0

0

2

L

6

8

10NHCL

% butanol

Fig. 22.10. (A) Variation of the R , values of Ga3+, Po4’ and Au3+ with the concentration of HCI used as eluent. (B) Variation of the R , values of Au” with the concentration of butanol in butanol-6 N HCI mixtures. (Reproduced from Metodi di Separazrone nella Chimica Inorganica, Vol. 1, 1963, p. 109, with permission [71].)

Adsorption of hydrophobic nature is also responsible for the separation of numerous mixtures of neutral coordination complexes. Table 22.1 lists the R , values of cis-dihalodiammineplatinum(I1)complexes. Evidently, as the size of the halogen increases, the R , value decreases. TABLE 22.1 R , VALUES O F cis-DIHALODIAMMINEPLATINUM(I1) COMPLEXES

Solvent, water; paper, Whatman No. 3MM; temperature, 5’C [71].

,

Complex Pt(NH3

R value 2

Pt(NH,),CIBr Pt(NH3)2Br2 Pt(NH3),C11 Pt(NH,), I 2

0.65 0.58 0.53 0.56

0.44

22.5. ION-PAIR OR OUTER-SPHERE COMPLEX FORMATION Metal ions with a completely filled first coordination sphere may still form a second sphere of coordination. This was first discovered by Werner, who noted that the color (and spectrum) of the very stable Co(NH,):- changed in the presence of sulfate ions. In the various systems used for separation, the most striking outer-sphere effects were noted in the paper electrophoresis of Co(II1) complexes, as best illustrated in Fig. 22.1 1. References on p. 8488

IN ORGANIC COMPOU N DS

8470

i

140 '50]

\

7 7 7 .

1

A

2

3

4

C

D

Fig. 22.1 1. Graphic representation of the electrophoretic movement of Co(III) complexes in various electrolytes. (A) Comparison of mono-, di-. and trichloroacetate (1 N ) . (B) Comparison of several divalent anions (0.1N ) . (C) Comparison of LiCI, LiBr, and NaCIO., (0.1 N ) . (D) Comparison of 0.1, 0.5, and 1 N trichloroacetate. Complexes: 1 = hexamminecobalt(II1); 2 = tris(ethylenediammine)cobalt(III); 3 = tris(dipyridyl)cobalt(111); 4 = Iris( o-phenanthroline)cobalt(IIl). (Reproduced from J . Chromutogr., 35 (1968) 201 1721.)

Chloride and other monovalent hydrated anions, such as acetate and nitrate, will form a nonspecific anion cloud, whch will retard all complexes considerably but to a similar degree. Sulfate, chromate, and most divalent anions will form hydrogen bridges to coordinated NH, or aquo groups, but not with groups such as dipyridyl or o-phenanthroline, which have no possibility for hydrogen bonding. This effect can be of such magnitude as to make trivalent cations behave like neutral species. Hydrophobic anions, such as perchlorate or trichloroacetate, will form "hydrophobic ion pairs", especial!y with voluminous hydrophobic coordination groups, such as dipyridyl or o-phenanthroline. Again, the effect can be very strong. In ion exchange, outer-sphere complexation between the sulfonic groups of a resin and the aquo or ammine groups of a complex has been shown to exist. It should be stressed here that inner-complex formation has also been observed. There is also evidence that outer-sphere complexation between, e.g., aluminate groups on the surface of alumina or silanol groups on the surface of silica and coordination complexes does play a part in the chromatography of such complexes on inorganic exchangers.

ION CHROMATOGRAPHY

B47 1

22.6. ION CHROMATOGRAPHY

A fascinating recent advance in analytical ion-exchange chromatography was introduced by Small et al. [4] (cf. Chap. 7.5.4). Because in ion-exchange chromatography a strong electrolyte is usually employed as eluent, continuous effluent monitoring by means of conductivity measurements is not possible, except in a few cases. In the commercial “Ion Chromatograph” (Dionex Corp.), weak acid salts are used as eluents for anions. The eluents pass over the hydrogen form of a cation exchanger (“suppressor column”), which removes the cation, leaving only a weak acid as background. The zones of strong electrolytes can then be recorded by their conductivity. Typical eluents are, e.g., carbonate-bicarbonate mixtures, and as the resins used have a very low capacity (0.007 meq/g) the concentrations of eluents can also be rather low (2 lop4M ) . Extensive work on a wide range of anions was published by Gjerde et al. [5]. Figs. 22.12-22.14 show some of the excellent separations obtained. They also demonstrate that separations can be obtained in as little as 10 min. Thus, ion chromatography is quite competitive with HPLC techniques.

-

1

HCOj

W

u)

z

0

a

W u)

W

d

z u)

B

d

P

v)

W

0 W lW

(L

h iK

a

n

0 I0

Form-

W

I-

W 0

0

5

10

15

TIME, min

20

25

0

I

I

5

10

I

I

15

20

TIME, min

Fig. 22.12. Separation of phosphate from all other anions in a diluted cola drink by ion chromatography M potassium benzoate, pH 6.25, on a column of XAD-2 (0.007 meq/g). (Reproduced from with 1 . J. Chromotogr., 187 (1980) 35, with permission [ 5 ] . ) Fig. 22.13. ion chromatography of 27.1 ppm acetate, 6.8 ppm formate, 5.1 ppm chloride, and 15.8 ppm nitrite on Vydac SC anion-exchange resin with 5 . M potassium benzoate, pH 6.25. (Reproduced from J. Chromotogr., 187 (1980) 35, with permission [5].) References on p . 8488

INORGANIC COMPOUNDS

8472

u1 W

z

0 W ln

a

:I-

iK

0

0

1

V

w

x

I-

w

a J

3

I

I

I

5

I0

15

I 20

I 0

5

10

15

20

TIME, min

Fig. 22.14. Ion chromatography of 7.7 ppm chloride, 29.5 ppm iodide, 28.5 ppm thiocyanate and 16.5 ppm sulfate and of the same mixture, diiuted by a factor of 10, o n XAD-1 (0.007 meq/g) with 5 . lo-’ M potassium phthalate, p H 6.25. (Reproduced from J. Chromarogr., 187 (1980) 35, with permission [ 5 ] . )

w 0

z 4

a m I 0 n

9

0

5

10

TME ,mm

I5

0

5 0 TIME, min

Fig, 22.15. Ion chromatography of 2.0 mg chromiurn(III), 39 p g platinum(1V). and 7.8 p g gold(II1) on XAD-4 (0.21 meq/g) with eluents shown. Detection at 225 nm. (Reproduced from J . Chromarogr., 188 (1980) 391. with permission 161.)

Fig. 22.16. ion chromatography of 1.3 mg copper(l1). 2.1 p g pa1ladium(ll), and 9.8 p g gold(ll1). For conditions. see Fig. 22.15. (Reproduced from J . Chromotogr., 188 (1980) 391, with permission 161.)

HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY

8473

Separations of metal ions are also possible on low-capacity resins, but Gjerde and Fritz [6] had to develop all-glass and plastic apparatus and use spectrophotometric detection for this purpose. Some of the separations obtained are shown in Figs. 22.15 and 22.16. These separations took as little as 10-15 min.

22.7. HIGH-PERFORMANCELIQUID CHROMATOGRAPHY Commercial instrumentation presently available is rather ill suited for the separation of metal ions. Stainless-steel columns cannot be used for eluents containing chloride ions, especially in acid solutions, and, because the various fitting and detector parts are usually also made of stainless steel or other metals, the choice of eluents is rather drastically limited. Early optimism prompted numerous applications of HPLC to metal chelates, but the methods either proved to be inapplicable to actual analytical problems or failed to improve the separations already in use. Most of these methods are listed in a recent review [7].

Ammonium lactate

Resin

Fig. 22.17. Apparatus for separations of rare-earth metals by ion-exchange chromatography with lactate. (Reproduced from J . Anter. Chenz. Soc. 76 (1954) 6229, with permission [8].) References on p . B488

INORGANIC COMPOUNDS

R414

High-speed separations would be very valuable for radioactive isotopes, especially those with short half-lives. A forerunner of HPLC (in general) may be found in the fundamental work on the transuranic elements [8], some ten years ahead of the invention of HPLC (cf. Preface). Fig. 22.17 shows the apparatus used, including a short column, 2 mm in diameter and packed with rather fine resin particles. Further, Fig. 22.18 is evidence that Thompson et al. [8] already considered the plate number at various flowrates. Their results (Fig. 22.19) show that a separation was effected in ca. 200 min, (100 drops at a rate of 2 min/drop), but the separation of Er-Ho was already complete in 30 min, which is clearly in the range of some modern HPLC separations. In order to effect HPLC separations of radioactive tracers, Horwitz et al. [9] built special apparatus in which only glass or PTFE parts were in contact with the eluent. The stationary phase, 25-30% di-(2-ethylhexyl)orthophosphoric acid in dodecane, was held on a support of porous silica microspheres. The columns, which were only 1 cm high, were operated at a maximum pressure of 500 psi. Fig. 22.20 shows a typical separation of 225Acand its daughter nuclides, which was effected in only 74 sec. Horwitz et al. also reported isotope enrichment of 4XCa/40Ca by use of a column 75 cm in length (ca. 30,000 theoretical plates) at 9OC, which indicates a considerable improvement over the previous attempts with “slow” chromatography. While there are difficulties in the use of commercial HPLC equipment for the separation of metal ions, this is not so for anions. Reeve [lo] separated anions on a

T me drop min

Fig 22 18 Width of elution peaks of rare-earth metals b‘s drop rate of ammonium lactate eluent in ion-exchange chromatography (Reproduced from J Amer Chem SOC,76 (1954) 6229, with permission 181 1

GEL CHROMATOGRAPHY

B475

Element Er Ho Dv Tb Gd Eu

Drop number

~0,721 13 17.2 23 33 52 626

Drop number

Fig. 22.19. Elution of homologous lanthanides with ammonium lactate eluent (ca. 2 min/drop=35 pl): column, Dowex 50. (Reproduced from J. Amer. Chem. Soc., 76 (1954) 6229, with permission [XI.)

column of cyano-bonded silica, Sil 60-D 10-CN (250 X 4.6 mm); eluted with 0.1 M Na,HPO,, 0.1 M KH,PO,, and 0.1%cetrimide, mixed with methanol (3:2); and detected the anions at 210-220 nm. Typical separations are shown in Figs. 22.21 and 22.22 (cf. also Chap. 22.13).

22.8. GEL CHROMATOGRAPHY Elementary chemistry textbooks still like to present the formation of an insoluble hydroxide, such as Fe(OH),, as a reaction obeying the law of mass action (solubility product), although it was realized as long as ca. 50 years ago during the work on “radiocolloids” that this picture is incorrect. A whole range of unstable and stable, soluble and colloidal polymers can be formed, depending on the concentration of the metal ion, the rate of addition of the OH- ion, temperature, etc. Very few of these hydrolysis polymers have been well characterized; e.g., zirconium(1V) occurs in dilute HCI as a polymer of ionic weight of about 20,000. Ths was, perhaps, the first polymeric substance separated by “gel filtration”, i.e. it was eluted from sulfonic ion-exchange resins [ 1 1 J, although, owing to its high charge, it should be strongly held if it were a monomer. At first sight, gel chromatography would be the ideal method for the isolation and characterization of such hydrolysis polymers. However, most of the present gel filtration media are unsuitable for such work. Sephadex gels have on their surface vicinal hydroxyl groups which complex readily with most metal ions at neutral pH (a References on p . 8488

INORGANIC COMPOUNDS

R476

225

e 9 A ~I I O d )

Ac225

0

2 2 ’ F r 14 Rrninl a7

I0 4

W

L

c ,E 103 3

c

c

0 3

V

I02

lution time in seconds

Fig. 22.20. High-speed separation of **’Ac and daughter nuclides. Column, Zorbax-SIL (5 pm), 10 X 2 mm ID with 30% (w/w) of di-(2-ethyIhexyl)orthophosphoricacid in dodecane as stationary phase; eluent, HNO,; flowrate, 17 cm,/min; temperature, 50°C. (Reproduced from J . Chromntogr., 125 (1976) 203, with permission 191.) 1

I

TIME (min)

Fig. 22.21. HPLC of halogen anions. Eluent, methanol-water (2:3), being 0.1 M Na,HPO,, 0.1 M KHZPO, and 0.1% (w/v) cetnmide with respect to the aqueous component; flowrate, 2ml/min. For other conditions. see text. Peaks: 1 = iodate; 2 = bromate; 3 = bromide; 4 = iodide. (Reproduced from J. C‘hrornnlogr., 177 (1979) 393, with permission [lo].)

GEL CHROMATOGRAPHY

I

B477

W

cn Z

8

cn W a

lx

P

0 W

t;; 0

T l M E imin) Fig. 22.22. HPLC of iodide and polythionates. Eluent, methanol-water (1 1 :9).For other conditions, see Fig. 22.21. Peaks: 1 = thiosulfate; 2 = iodide; 3 = trithionate; 4 = tetrathionate; 5 = pentathionate. (Reproduced from J. Chromatogr., 177 (1979) 393, with permission [lo].)

typical compound of this type is the “glycerate of iron” of the British Pharmacopoeia). Hence, these ions leave a trail when applied in high concentrations, and they are adsorbed altogether in low concentrations. Porous glasses and porous silica (and their derivatives) usually have on their surfaces a high concentration of silanol groups which also interact strongly with monomeric and polymeric metal ions. In spite of these shortcomings, quite a few polymeric hydrolytic species could be separated on gel-filtration media, e.g.: polymeric ruthenium [ 121, polymeric rhodium(II1) [ 131, and soluble ferrocyanides [ 14- 161. The movement of small monomeric ions inside gel-filtration media is largely governed by ion exchange with residual carboxyl groups, ion exclusion due to these groups, or hydrophobic adsorption, which is rather strong on Sephadex LH-20, where also salting-out effects can be observed [ 17). Gel chromatography has been used to study the interaction between metal ions and large molecules, such as proteins, dextrans, and polyphosphates. Most of the early work discussed in an excellent review by Yoza [18]. Another fascinating area that can be studied by gel chromatography deals with the interactions between inorganic polymers and small ions. For instance, the zirconium hydrolysis polymer is excluded from Sephadex, while small ions, such as chromate, are not. When a mixture of polymeric zirconium and chromate is chromatographed on Sephadex G-10, there is a slow-moving yellow band as well as a yellow excluded band, showing clearly that the polymer binds some of the chromate [ 191. References on p . 8488

INORGANIC COMPOUNDS

8478

22.9. GAS CHROMATOGRAPHY The early literature on GC of inorganic compounds was reviewed by Tadrnor [20], and there are also monographs by Guiochon and Pommier [21] and by Moshier and Sievers (221 and a review by Uden and Henderson [23]. We shall mention here only some of the main topics of research. GC separation of metals presupposes that a volatile derivative can be prepared having properties suitable for the available apparatus. Trifluoroacetylacetone complexes and similar derivatives fulfill these requirements, and some useful methods for some metal ions, notably for beryllium and chromium, have been reported. They seem to be competitive with other methods, such as atomic absorption spectrometry or radioactivation analysis [24-271. Metal organic compounds often have suitable properties for GC. For instance, inorganic mercury can be derivatized and detected at the 0.00251pprn level [28]. Also, the organic compounds of astatine were characterized by GC (see Fig. 22.23) ~91. Volatile metal chlorides have been either quantitatively determined by G C (e.g., germanium or arsenic [30]) or GC was used for studying their thermodynamic properties [31]. Special apparatus has to be used for the rather corrosive volatile \ halides.

70

60

50

40

30

20

10

0

Fig. 22.23. GLC separation of alkyl astatides, produced as a result of exchanging astatine, adsorbed at the column inlet in the form of astatines, with iodine in alkyl iodides. Column, 2 m X 4 mm ID, 10% dinonyl phthalate on Chromosorb G; carrier gas, helium; flowrate, 30 ml/min; column temperature, 95°C. (Reproduced from J. Chromotogr., 60 (1971) 414, with permission 1291.)

22.10. RESOLUTION OF OPTICAL ISOMERS Enantiomeric pairs of chelate complexes of the type [Co(en),I3' or [CO(OX),)~-have been separated by using both optically active adsorbents and optically active eluents. For example, the enantiomers of [Co(en),13+ were separated on CM-Sephadex with disodium D-tartrate as eluent [32]. In this kind of separation, ap-

RESOLUTION OF OPTICAL ISOMERS

8479

parently ion-pair formation between an optically active anion (such as tartrate) and the two forms of the chelate complex is responsible for the separation [33]. Similar results were also obtained by paper electrophoresis with optically active electrolytes (usually tartrate or antimonyl tartrate for complex cations; and strychnine, cinchonine, etc. for complex anions). It is usually considered necessary for the separation of optical isomers that a “three-point’’ adsorption or complexation is operating. The three points are usually hydrogen bonding and/or ionic attraction. However, there is evidence from paper electrophoresis experiments that separations are possible even when the conditions for a “three-point’’ interaction are nonexistent or unlikely, as is the case in the resolution of the optical isomers of [Fe(II)(dip)3]2’ in tartrate [34-361. Neutral tris(aminoacidato)cobalt(III) complexes were also separated on ion exchangers (e.g., the strong cation exchanger TSK 211), eluted with tartrate or antimonyl tartrate. Fig. 22.24 shows that the optical activity on one ligand (D- or L-serine) yields a separation with antimonyl tartrate (or with tartrate), but not with sulfate as eluent [37]. NaZ SO,,

Na 2 d-tar t

Na2(Sb2d-tart2)

Fig. 22.24. Elution curves of fac-[Co(L-ser)*(P-ala)] and fac-[Co(~-ser),(P-ala)] by ion-exchange chromatography. Column, 250 X 4 mrn ID, stainless steel, packed with TSK 21 1 strongly acidic cation exchanger; eluent, 0.05 M aqueous Na,SO,, 0.1 M aqueous Na,D-tart or 0.1 M Na,[Sb,(o-tart),]. A(L), A(L), A(D) and A(D) refer to the complexes with A or A configuration containing L- or D-aminoacidato anions. (Reproduced from J. Chromatogr., 175 (1979) 317, with permission [37].) References on p . 8488

INORGANIC COMPOUNDS

~480

22.1 1. SEPARATION OF COORDINATION COMPLEXES Unlike the reversible complexes of the type FeC12+,many metal ions, especially f i 3 7 , Ru' + , and C r 3 +, can form extremely strong complexes with ammonia, amines. substitued phosphines, and substituted arsines and stibines. For example, one of the simplest Co(lI1) complexes, namely Co(NH,);+, can be heated to several hundred degrees or treated with KOH without undergoing decomposition. I t forms a hydroxide which is a strong base and, in solution, absorbs CO, from the atmosphere. Such complexes can be subjected to chromatography or electrophoresis in a wide range of acids or bases without any risk of decomposition. Most methods for the preparation of such stable complexes involve. e.g., the oxidation of Co(I1) (by air or H,O,) in the presence of the ligands, e.g., NH,OH or ethylenediamine. Usually, an array of compounds forms, from which the desired compound is isolated by crystallization (by evaporation or by addition of ethanol or acetone). One of the uses of chromatographic techniques is to show that in numerous syntheses the isolated complex is actually a mixture of as many as six compounds (e.g., [CO(NH,),(NO,),]~ or Co(tn),Cl,). A pure complex can then be isolated by preparative chromatography for the first time. This field has been reviewed [38], and we can therefore restrict ourselves to mentioning only some of the interesting features. Paper chromatography has maintained its popularity as a convenient small-scale preparative technique [39,40]. Quantities up to 30 mg can be applied as a line to a sheet of Whatman No. 3MM paper, which is developed overnight. The zones, which are usually colored, can be excised and eluted chromatographically. The amount so

co",

900 I 7-- 1 - 0 1 0 N HCIO.,

aoo

1

--

T

- - -1 ON H C I G ~-

-

-*-5 O N mag-

A

CriH,Oi,

.I

3*

Resin

-.

,.

Fig. 22.25. Elution curve of a mixture of Cr(I1I)-thiocyanate complexes from Dowex-50 cation-exchange resin. (From J . Anier Chem. Soc., 82 (1960) 2963. as reproduced in ref. 38.)

COORDINATION COMPLEXES

B4R I

obtained is usually sufficient for further reactions, analyses, and spectroscopic studies. Ion-exchange column chromatography is employed in practically all synthetic work, usually for purification or for the separation of several complexes from a reaction mixture. The amounts obtained are again of the order of 10-100 mg. A typical example is shown in Fig. 22.25. violet winered

red- yellow- yellow orange orange

Fig. 22.26. Moving-boundary ionophoresis of mixed ligand complexes [Cr(SCN),(CN),+,I3-,

x = 2 . . .6, in acetonitrile. (Reproduced from J . Chromufogr., 50 (1970) 319, with permission 1431.)

where

Fig. 22.27. Paper electrophoresis of the chlorobromo and bromoiodo complexes of osmium(1V). (Reproduced from Chromofogr. Rev., 6 (1964) 191, with permission 131.) References on p . B488

8482

INORGANIC COMPOUNDS

Alumina was advocated for the separation of coordination complexes by Jensen et al. [41] mainly because colored complexes could be easily distinguished on the white alumina but not on the brown ion-exchange resin. In these separations, which were carried out with aqueous eluents, alumina functions essentially as an ion exchanger (surface aluminate groups) with possibly an additional outer-sphere complexing effect. HPLC has not been applied extensively so far. Its possibilities are indicated by preliminary work 1421, which demonstrated one of the attractive features of the technique, i.e. that spectra can be obtained on the eluate by stop-flow methods. Electrophoretic methods, TLC, and HPTLC have been applied widely, mainly in the study of reactions of coordination complexes. A beautiful displacement electrophoretic separation of a series of Cr(II1) thiocyanato-cyano complexes is shown in Fig. 22.26 (431. A paper-electrophoretic separation of chlorobromo and bromoiodo complexes of osmium(1V) is shown in Fig. 22.27 [3]. 22.12. SCANDIUM, YTTRIUM, THE RARE EARTHS, AND ACTINIUM Together with Sc, Y, and Ac, the rare earths constitute 18% of the elements of the periodic table. There was no effective method for separating these elements before the advent of chromatography. The first successful analytical separations date from the Second World War 144,451 and are among the best examples of how separations

Fig. 22.28. TLC separation of (a) cerium earths and (b) ytterbium earths. Eluent: (a) 0.5 N HCI; (h) 4 N HNO,. Layers ( 5 0 0 pm) were prepared from a mixture of 30g silica gel. 12 ml di-(2-ethylhexyl)phosphoric acid and 34 ml I-butanol. (Reproduced from J . Chromarogr.. 24 (1966) 153, with permission [48].)

Sc, Y, THE RARE EARTHS, AND Ac

B483

can be achieved by using a suitable complexing agent on an ion exchanger. Since then, separations have been devised by numerous column systems, including HPLC [46,47], by TLC (Fig. 22.28) [48,49], paper electrophoresis (Fig. 22.29) [50], and isotachophoresis (Fig. 22.30) [ 5 11. As chromatography appeared to be the best method yet for preparing gram quantities of the rare-earth elements, several laboratories have devised large-scale

Fig. 22.29. Qualitative paper-electrophoretic analysis of mixtures of rare-earth metal ions, carried out in the ligand buffer system Zn2+-ZnLZ- (pH2). (A) Flint stones; (B) rareearth alloy. Paper, Whatman No. 2; potential drop, 28-30 V/cm; concn. of free ligand, 10- ”.’ M. (Reproduced from J. Chromaiogr., 74 (1972) 325, with permission (501.) References on p . B488

INORGANIC‘ COMPOUNDS

8484

1

I

I

I

17

18

19

20

Tirnejrnln

Fig. 22.30. Isotachopherogram for the simultaneous separation of lanthanides. (a) Potential gradient; (b) differential gradient. Leading electrolyte: 0.027 M KOH, 0.015 M 2-hydroxyisobutyric acid, acetic acid, and 0.00251 poly(vinv1 alcohol), pH 4.92. Migration current, 225 PA: chart speed, 40 mm/min; sample, 5.0 1-11 of a 10- M solution of mixed lanthanides. 1 = K’ , 2 = N a f , 3 = La” , 4 = C e ’ + , 5 = Pr’ . 6 = N d ” . 7 = Sm” . 8 = Eu’-. 9 = G d 3 + , 10=Tb’+, 1 1 = Dy-” , I2 = H o 3 + , 13 = E r ” , I4 = T m 3 + , 15 = Yb’ * , 16 = Lu3 . . 17 = P-Ala. (Reproduced from J . Chrumarogr., 205 (1981) 95, with permission Ill.,

‘

’

preparative separations (for a typical example, see Fig. 22.3 1). Spedding’s group [52-541 laid the foundations for this technology with their demonstration that displacement development is the most efficient preparative method. For most of these methods organic complexing agents were used; first citric acid and later a-hydroxybutyric acid as well as lactic acid and EDTA, which were found to yield better separation factors (i.e., larger differences in stability constants). Nitric acid can also be used for the separation of the lighter rare-earth elements [ 5 5 ] .

0 8

sm 35

40

45

50

1

7:

55

60

65

Volume of eluate (Iltres)

Fig 22 31 Preparative ion-exchange chromatography of rare-earth elements Elution of 1 713 g equirnolar mixtures of SmzO, and Nd,O, from a 170 X 2 2-em column of Amberlite IR-100 (30-40 mesh), with 0 1% citrate at p H 5 0, 5 5 , and 6 0, at a flowrate of 0 5 cm/min 0. Total R,O,, 0 .S m 2 0 3 ,8 ,Nd,O,, broken vertical lines indicate amount of overlap between Srn and Nd bands (From Discusr Famduy Suc , 7 ( 1949) 214. as reproduced in ref 73 )

CONDENSED PHOSPHATES

8485

22.13. CONDENSED PHOSPHATES

The chemistry of condensed phosphates could not be investigated before the advent of chromatographic methods. There are several good reviews and even a book on the main developments in this field [56-581. Chromatography is now the classical (if not the only) method for characterizing new phosphates or mixed condensed arseno-phosphates. After it was realized that the Ca2+ and Mg2+ ions present in Whatman papers (due to their manufacture in hard water) must be removed by suitable acid washes, PC was used in all pioneering work. Subsequently, excellent TLC, ion-exchange, gel filtration, and HPLC methods have been described. In retrospect, these methods certainly improved quantitative analysis and speeded up the separations, but they did not materially improve the rather adequate separations obtained by PC. Figs. 22.32-22.34 show some typical examples.

Acidic solvent

Fig. 22.32. Separation of a mixture of phosphorus oxoacids by two-dimensional PC. Alkaline solvent, 2-propanol-2-butanol-water-20% ammonia (40: 20 : 39 : I); acidic solvent, 2-propanol-water-20% trichloroacetic acid-25% ammonia (700 : 100 :200 :3). Compounds: 1 =orthophosphate; 2 = pyrophosphate; 3 = triphosphate; 4 = tetraphosphate; 5 = pentaphosphate; 6 = hexaphosphate; 7 = heptaphosphate; 8 = octaphosphate; 9 =Graham salt; 10= trimetaphosphate; 11 = tetrametaphosphate; 12 = hypophosphite; 13 = phosphite; 14= hypophosphate. (Reproduced from Metodi di Separartone nella Chtmica Inorganica, Vol. 1, 1963, p. 199, with permission [58].) References on p . 8488

INORGANIC COMPOUNDS

8486

05

04

04

03

s

.z

03

02

0.2

01

U L

r

h

8'

05

04

03

2

04

4

3

and tetramete

02

0.3

2 sP) -

9 C

-

'-

Y ~

0.2

01 10

20

30

40

50

70 00 90 100 Fraction number

60

no

120 130 140 150 160

Fig. 22.33. Ion-exchange chromatography of a polyphosphate mixture. Ion exchanger. Dowex 1-X4; gradient elution. (a) Borate buffer. p H 8.0: (b) ammoniacal buffer. pH, 9.3. (From J . Biochem. (Tokyo), 44 (1957) 65. as reproduced in ref. 58.)

n=5

J

. -

1=

15

1

8 '

I

n = 20

1

n=

-A

n = 30

. 1 I

I

2

3

4

Time ( h

5

6

)

Flg. 22.34. HPLC of Na,FQ4. Na4P20, and Na,+,P,O,,+, (for ii = 5 and i i = 10). Column, 100 X 9 mm ID, Hitachi 2630 anion-exchange resin (4% crosslinked). Eluent, NaCl-5 m M Na4EDTA, p H 10.0; gradient, convex from 0.22 M NaCI ( r = 0) to 0.53 M NaCl ( r = 6 h). (Reproduced from J . Chromufogr., 172 ( I 979) 13 1, with permission 1741.)

SILICATES

B487

22.14. SILICATES

The early literature on PC contains claims of the separation of polysilicates, which, however, could not be verified. A gel-chromatographic separation of monosilicic acid from polysilicic acid on a Sephadex G-25 column was reported by Tarutani [59]. Intermediate species seem to be too unstable to be isolated by this method. TMS derivatives of condensed silicates were separated by GC [60,61], but the method of preparation of the derivatives seems to have had a large influence on the species isolated. Decomposition during derivatization seemed excessive. More recently, Shimono et al. [62] have reported both GC and gel-filtration separations of TMS derivatives of polysilicates. Typical separations are shown in Figs. 22.35 and 22.36. Even colloidal silica can be studied by gel filtration [63].

Q4M10

L

5

10

15

20

25

L

30

35

Retention tine (min) Fig. 22.35. Gas chromatograms of (a) trimethylsilyl olivine and (b) trimethylsilyl laumontite. Column, 3.0 m X 3.0 mm ID, packed with 21% OV-l on Chromosorb W AW DMCS (60-80 mesh); carrier gas, helium; temperature, programed from 100 to 300OC at S°C/min; detector, flame ionization. Q is one tetrahedron corresponding to one SiO, unit in a condensed silicate system; M is the (CH,),SiO,/, atomic group resulting from silylation. (Reproduced from J. Chrornatogr., 197 (1980) 59, with permission 1621.) References on p . B488

INORGANIC COMPOUNDS

€3488

QM4

HMDS

Fraction number

Fig 22 36 Gel chromatogram of (a) trimethylsilql olirine and (b) trirnethylsilyl ldumontite Two 90 \* 1 5-cm I D column\, total kolume ca 318 ml Gel. Bio-Beads S-XI. eluent. 2-propanol-chloroform

12 3 ) Q is one tetrahedron corresponding 10 one SiO, unit in a condensed silicate system, M is the (CH,),SiO, atomic group resulting from silqlation (Reproduced from J Chromatogr, 197 (1980) 59, h i t h permiswm [hZ])

REFERENCES 1 M .Lederrr and C. Majani. Chromarogr. Rec , 12 (1970) 239. 2 U.A.Th. Brinkman. G. de Vries and R. Kuroda, J. Chromarogr., 85 (1973) 187. 3 F.. Blasius and W. Prretz. Chromarogr. Rec.. 6 (1964) 191. 4 H. Small. T.S. SteLens and W C. Bauman. Aria/ Chem.. 47 (1975) 1801. 5 D T. Gjerde, G. Schmuckler and J.S. Fritz. J Chroniatogr.. 187 (1980) 35. 6 D.T. Gjerde and J.S. Fritz. J . Chroniarogr, 188 (1980) 391. 7 G. Schwedt. Chromarographta. 12 ( 1979) 6 13. h S.G. 1-hompson. B.G. Harvey. G.R. Choppin and G.T. Seaborg. J . Amer. Cheni. Soc., 76 (1954) 6229. i) t . P . Howitz. ".ti. Delphin. C.A.A. Bloomquist and G.F. Vandegrrft. J . C'hromarugr.. 125 (1976) 203. 1 0 R . N . Reeve. J Chromuiogr, 177 (1979) 393.

REFERENCES

B489

1 1 J.A. Ayres, J. Amer. Chem. SOC.,69 (1947) 2879. 12 I. Kitayevitch, M. Rona and G. Schmuckler, Anal. Chim. Acta, 61 (1972) 277. 13 M. Sinibaldi and A. Braconi, J . Chromatogr., 94 (1974) 338. 14 H. Saito and Y. Matsumoto, J . Chromatogr., 168 (1979) 227. 15 Y. Matsumoto, M. Shirai and H. Saito, Bull. Chem. Soc. Jap., 41 (1975) 210. 16 D. Corradini and M. Sinibaldi, J . Chromatogr., 187 (1980) 458. 17 V. Di Gregorio and M. Sinibaldi, J. Chromatogr., 129 (1976) 407. 18 N. Yoza, J. Chromatogr., 86 (1973) 325. 19 M. Sinibaldi, G. Matricini and M. Lederer, J . Chromatogr., 129 (1976) 412. 20 J. Tadmor, Chromatogr. Rev., 5 (1963) 223. 2 1 G. Guiochon and C. Pommier, Gas Chromatography in Inorganics and Organometallics, Ann Arbor Sci. Publ., Ann. Arbor, MI, 1973. 22 R.W. Moshier and R.E. Sievers, Gas Chromatography of Metal Chelates, Pergamon, New York, 1965. 23 P.C. Uden and D.E. Henderson, Analyst (London), 102 (1977) 889. 24 L.C. Hansen and W.G. Scribner, Anal. Chem., 43 (1971) 349. 25 W.R. Wolf, M.L. Taylor, B.M. Hughes, T.O. Tiernan and R.E. Sievers, Anal. Chem., 44 (1972) 616. 26 M.S. Black and R.E. Sievers, Anal. Chem., 48 (1976) 1872. 27 J.G. Lo and S.J. Yeh, J . Chromatogr. Scr., 18 (1980) 359. 28 P. Jones and G. Nickless, J . Chromatogr., 89 (1974) 201. 29 M. Gesheva, A. Kolachkovsky and Yu. Norseyev, J. Chromatogr., 60 (1971) 414. 30 B. Iatridis and G. Parissakis, J . Chromatogr., 122 (1976) 505. 31 J. Rudolph and K. Bachmann, J . Chrornatogr., 187 (1980) 319. 32 Y. Yoshikawa and K. Yamasaki, Inorg. Nucl. Chem. Lett., 6 (1976) 523. 33 H. Nakazawa and H. Yoneda, J. Chromatogr., 160 (1978) 89. 34 L. Ossicini and C. Celli, J . Chromatogr., I15 (1975) 655. 35 V. Cardaci, L. Ossicini and T. Prosperi, Ann. Chim. (Rome), 68 (1978) 713. 36 V. Cardaci and L. Ossicini, J. Chromatogr., 198 (1980) 76. 37 S. Yamazaki, T. Yukimoto and H. Yoneda, J. Chromatogr., 175 (1979) 317. 38 V. Carunchio and G. Grassini Strazza, Chromatogr. Reu., 8 (1966) 260. 39 0. Bang, A. Engberg, K. Rasmussen and F. Woldbye, Acta Chem. Scand., 29 (1975) 749. 40 F.P. Dwyer, T.E. MacDermott and A.M. Sargeson, J . Amer. Chem. Soc., 85 (1963) 2913. 41 A. Jensen, J. Bjerrum and F. Woldbye, Acta Chem. Scand., 12 (1958) 1202. 42 G . Grassini Strazza and C.M. Polcaro, J. Chromatogr., 147 (1978) 516. 43 E. Blasius, H. Augustin and U. Wenzel, J . Chromatogr., 50 (1970) 319. 44 B.H. Ketelle and G.E. Boyd, J . Amer. Chem. Soc., 69 (1947) 2800. 45 E.R. Tompkins, J.X. Khym and W.E. Cohn, J. Amer. Chem. Soc., 69 (1947) 2769, and the other papers in this issue. 46 F. Schoebrechts, E. Merciny and G . Duyckaerts, J . Chromatogr., 174 (1 979) 35 1 . 47 F. Schoebrechts, E. Merciny and G. Duyckaerts, J . Chromatogr., 179 (1979) 63. 48 H. Holzapfel, Le Viet Lan and G. Werner, J . Chromatogr., 24 (1966) 153. 49 H. Holzapfel, Le Viet Lan and G. Werner, J . Chromatogr., 20 (1965) 580. 50 V. Jokl and Z. Pikulikova, J. Chromatogr., 74 (1972) 325. 51 I. Nukatsuka, M. Taga and H. Yoshda, J. Chromatogr., 205 (1981) 95. 52 J.E. Powell and F.H. Spedding, Chem. Eng. Progr., Symp. Ser., 55 (1959) 101. 53 D.B. James, J.E. Powell and H.R. Burkholder, J . Chromatogr., 35 (1968) 423. 54 F.H. Spedding, Discuss. Faraday Soc., 7 (1949) 214. 55 K. Ishida, Bunseki Kagaku (Jap. Anal.), 19 (1970) 1250. 56 H. Hettler, Chromatogr. Rev., 1 (1959) 225. 57 H. Grunze and E. Thilo, Die Papierchromatographie der kondensierten Phosphate, Akademie Verlag, Berlin, 1954/1955. 58 J.P. Ebel, in Metodi di Separazione nella Chimica Inorganrca, Vol. 1, CNR, Rome, 1963, p. 199. 59 T. Tarutani, J. Chromatogr., 50 (1970) 523. 60 G. Garzo, D. Hoebbel, Z.J. Ecsery and K. Ujszhzi, J. Chromatogr., 167 (1978) 321. 61 G. Garzo and D. Hoebbel, J . Chromatogr., 119 (1976) 173.

B490

62 63 64 65 66 h? hX h9

70 71 72 73

74

IS O R G A N 1C COMPOUNDS

T. Shiinono. H . Takagi. T. Isobe a n d T. Tarurani. J . ChrotnuroKr., 197 (1980) 59. J . J . Kirkland. J Chroniarogr., 185 (1979) 273. E. Blasiuh. in Muted di Seporu-ione n e h Chimica Inurgunrra. Vol. I . CNR, Rome, 1963. p. 141. K.A. Kraus and F Nelson, J . Chromutugr.. 1 (1958) X. R.A. Guedec de Carvalho. J . Chromatogr., 1 (1958) XII. E. Cerrai and G. Ghersini. J . Chromarogr.. 24 (1966) 383. S. Przeslakouski. C’hromurogr. Rev.. I2 (1970) 383. E.. Lederer and M Lederer. Chromutogruphy - A Recien. of Princrples und Applicuriotrs. Elsevier, Amsterdam. 2nd Edn., 1957. p. 468. K. Kauazu. J Chromxogr.. 137 (19771 381. M. Lederer. in Metodi dr Sepurmroiie nellu Chrnirca Inorgunrcu, Vol. I . CNR. Rome. 1963, p. 109. M . Lederer and M .M a u e i . J . Chromarogr, 35 (1968) 201. tt. Lederer and M. Lederer, Chromor0graph.v - A Review of Principles and Applrcutrons. Elsevier. Amsterdam. 2nd Edn.. 1957. p. 448. H. Yamaguchi. T. Nakamura. Y . Hirai and S. Ohashi, J . Chroniutogr., 172 (1979) 131.