Ion-Exchange Thin-Layer Chromatography of Metal Ions in Organic Solvent - Hydrochloric Acid - Complexing Agent Media

R. K u r o d a * / N . Hosoi

Laboratory for Analytical Chemistry, Faculty of Engineering, University of Chiba, Yayoi-cho, Chiba, Japan

Key Words

Thin-layer chromatography Ion-exchange Metal ion Trioctylphosphine oxide

S u m m a r y

Thin-layers of strongly basic or strongly acidic ion- exchange resins (Dowex 1 or Dowex 50), mixed with a plain cellulose, Avicel SF, have been used to investigate the chromatographic behaviour of 40 metal ions in acetic acid - hydrochloric acid - complexing agent media. The CIESE (combined ion-exchange-solvent extraction) effect, proposed by Korkisch, is noticed for scandium and thorium in the anion-exchange system involving trioctylphosphine oxide (TOPO) as the com- plexing agent, the system providing a basis on the specific separation of both elements. In the cation-ex- change system involving TOPO, the metal ions are distributed chromatographically, so that the system allows multicomponent separations to be carried out. The system also reveals the CIESE effect for zirconium and hafnium.

The present investigations were carried out to study the chromatographic behaviour of metal ions in organic solvent- hydrochloric acid trioctylphosphine oxide (TOPO) media to find the applicability and usefulness of this CIESE system. Thin-layer chromatographic technique was employ- ed because it allows the prompt and clearcut inspection of individual chromatograms. R v values of metal ions for Dowex 1, X-8 in various organic solvent - HC1 - TOPO media were systematically measured. Among the organic solvents tested, acetic acid was found to be the most appro- priate, giving excellent selectivity for scandium and thorium in anion-exchange chromatography and allowing multi- component separations to be effected in cation-exchange chromatography.

Exper imenta l

Ions

0.1M metal stock solutions in 3M HC1 were prepared in most cases. Solutions of Se(IV), Te(IV), Mo(VI). W(V[) and Re(VII) were prepared by dissolving the sodium or am- monium salts in water to yield respective 0.1 M solutions. 0.1M TI(!) and Pb(II) solutions were 3M in HNO3. The solution of Nb(V) was the same as reported previously [9 ].

Introduct ion

Analytical ion-exchange behaviour of many metal ions in organic solvent-hydrochloric acid mediahas been extensively investigated by many researchers [1,2]. The adsorptions of elements from such mixed aqueous-organic solvent systems are often considerably higher than that from pure aqueous solution of comparable acidity. Accordingly, the separations in these organic solvent systems are often lacking the selectivity. Korkisch introduced the concept of combined ion-exchange-solvent extraction (CIESE) effect [3], reveal- ing the increased selectivity of the technique [4-8] .

* To whom correspondence should be sent.

Preparation of Plates

Both strongly basic anion-exchange resin Dowex 1, X-8 (200 to 400 mesh) in the chloride form and strongly acidic cation-exchange resin Dowex 50, X-8 (200 to 400 mesh) in the hydrogen form were used as adsorbents. 1:3 Mixtures of the resin to a microcrystalline cellulose powder Avicel SF (F.M.C., Marcus Hook, Pa., USA) were used as the substrate. 12g of Avicel SF was swollen with 150ml of water with stirring, centrifuged and then slurried with 16ml of distilled water. 4g of either Dowex 1 or Dowex50 resin was added to the slurry, mixed thoroughly and spread over five 20x20cm glass plates at an applied thick- ness of 250/2m. The plates were air-dried for 1 h, then heated at 45 ~ for 3h and stored in a desiccator over

Chromatographia Vol. 14 No. 6, June 1981 Originals 359

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saturated KBr solution. The metal ions (0.5 #1 of solution) were applied to the layers and developed for 15cm in rectangular glass tanks by the ascending technique after equilibration for 1 h. The following eluents were employed: a) mixtures of glacial acetic acid and 1, 6 or 12 tool/1 HC1

( 19 : 1) with and without TOPO; b) mixtures of methanol and 6mol/l HC1 (19:1) with and

without TOPO; and c) mixtures of acetone and 6mol/1 HC1 (19:1) with and

without TOPO, where the concentration of TOPO in each mixture was 0.1 tool/1.

The metal ions were detected as described previously [10]. Exceptions were V(IV), Mn(II) and Nb(V), which were detected by spraying with 0.1% ethanolic 1-(2-pyridylazo)- 2-naphthol, followed by 1 tool/1 NaOH; Sc(IIl), Y(III), the rare earths, Zr(IV), Hf(IV) and Th(IV) with 0.1% aqueous xylenol orange, followed by an acetate buffer solution (pH 5); and As(II1,V) with 10% SnC12" 2H20 in conc.HC1.

Results and Discussion

Table I lists the Rv values of 20 metal ions on Dowex 1 resin layers both in organic solvent - 6M HC1 (19:1), 0.1M in TOPO media and in the same organic solvent - 6M HCI (19 : 1) media for the purpose of comparison. The adsorp-

tion data are given for three organic solvent, i.e., methanol, acetone and acetic acid. For the solvent system involving acetic acid there are marked differences in adsorption behaviour of several metals between with and without TOPO media for anion-exchange resin layers. This is the case for Sc(llI), Ti(IV), Zr(IV), Hf(IV) and Th(IV), which migrate up the plate, yielding distinctly higher R~. values in the presence of TOPO. They are the elements known to be extracted in water-immiscible solvent with TOPO, but do not always represent the group extractable with TOPO from hydrochloric acid; e.g. Au(III) can be extracted from 1-8M HC1 with the distribution coefficient of as high as 7.5 to 9.5 " 104 [11]. Apparently TOPO does not exercise any effect on the R F value of Au(llI). This is reflected merely an extremely high adsorbability of AuCI2 on the Dowex 1. This is also the case for U(VI), which is highly extractable in water-immiscible solvent with TOPO, but exhibits the same behaviour regardless of the presence of TOPO. Therefore, the R F values appe;ir to be controlled by some difference between anion-exchange affinity scale to Dowex 1 and the extraction capability with TOPO, the difference being difficult to quantify.

The acetic acid - 6M HC1 - TOPO system makes a basis for the selective separation of Sc(III) and Th(IV); Zr(IV) and Ti(IV) streak significantly, and Hf(IV) partly remains at start.

Tab le I. R F values o f metal ions on D o w e x 1, X - 8 layers.

So lven t S t : o rgan ic so lvent - 6 M HCI ( 1 9 : 1 ) . So lven t S 2

organ ic so lven t - -6 M H C 1 ( 1 9 : 1 ) , 0 . 1 M in TOPO

Tab le I I . R F values o f metal ions on D o w e x 50 , X - 8 layers.

So l ven t St : o rgan ic so lvent - 6 M H C l ( 1 9 : 1 ) . S o l v e n t S 2:

o rgan ic s o l v e n t - 6 M H C 1 ( 1 9 : 1 ) , 0 . 1 M i n T O P O

R F x 100

Methanol Acetone Acetic acid

Metal

Au( l l l ) Ba(ll} Ca(tl) Fe( l l l ) Oa(l l t}

Hf( IV) Hg(tl) In(t i t )

La( l l t ) Mo(Vl ) Sc(tl l) Sin ( I l l )

Sn(IV) Sr(l l) Th(IV) Ti(IV)

U(Vl) Yb( l l l )

Zn( l l ) Zr(IV)

$1 $2

0 - 2 0 -1 4 - 2 8 4 - 2 7

80-91 7 0 - 8 9 0 - 4 O - 6 0 - 3 0 - 5

0 - 5 5 6 0 - 8 8 " 0 - 2 0 - 2 0 - 3 0 - 6

$1 $2 $1 82

0 - 2 0 - 2 2 3 - 4 8 3 1 - 5 3

0 - 2 2 11 -27 J i

0 - 3 0 - 4 0-3 0--3

0 - 6 67-91 0 - 2 0 - 2 0 - 3 0 - 2

0 - 2 0 - 2 0 - 2 0 - 2 0 - 2 0-2

0--70 0 - 6 7 1 5 - 5 6 " 0.-

20-61 .. 8 3 - 9 2 a

0 - 6 6 7 - 9 5 0 - 5 0 - 1 2 4 - 3 0 * 0 - 5 7 -

89 - 9 6 0--3 0--19 0--78 0--4

75--93 0--7 0--12 0--12 0 - - I00 O--3 0--2 20--36

67--95* 0--8 23--50.. 0--5 54--97

0--99 0--3 0--16, 0--7

78--96 0--13 0--2 0--83 0 - 9

0--62 16--62 0--2 O--2 0--1 0--28

28--81 * 72--98 0--7 0 - 6 4 23--70 0--3 0--2 0--5 0--23

3 1 - 4 5 28--44 0 - 2 0 - 5 9 53--91" 0--2

53--83 44--94 0--2

0--4 0--13 0--8 0--66 49--74 0--3

0--2 0--2 0--3 0--28 0--1 .. 0 - 1 6

40--88

0--21 0--6

76 --94 0 - 1 2 0 - 4

27 --43 52--90

0 - 8 8

0--3 0--7

0--2 0--95

a Mark .. represents weak streak. * Faint spot remains at the start.

La( l l l ) Mo(Vt} Sc(l l l ) Sm(l l l ) Sn(IV)

Sr(l l) Th(IV) 0 3 0 - 1 7 Ti(IV) 0--3 0 - 9 U(VI) 0 - 7 0 - 2 9 YB(I l I) 0 - 3 0 - 3 Zn(l l ) 4 9 - - 4 9 - .

52-69. . 52--66.- 73 74

Zr(IV) 0 - 7 0 - 3

" I Methanol . Acetone Acetic acid

Metal S 1 , S 2 S 1 S 2 S t ,, S 2 , I ,

' I " +'

Au( l l l ) 8 3 - 9 3 : 9 3 - - 9 9 9 2 - - t 0 0 9 4 - 1 0 0 31 .., 63- - t00 4 a 4 --83

Ba(ll) 0 - -1 ,0 1 0--1 0 - 2 ~ 0 . 2 0--2 i

Ca(ll) 0--2 0 z l I 0--1 0 - 2 0 - 2 0 - 1 Fe(l l l ) 4 - 1 3 9 - 2 1 , '50--75 56--87 4 0 - 8 5 Ga(l l l ) 7 - 2 1 " 5--13 50--100 51:. 56--98 5 0 - 9 7 *

' " ' i - 89--99" '

Hf(IV) 0--25 61--83" 0--5 64 . . . 0--5 57--86* -77--97

Hg(l l ) 86--94 86--96 95--99 88--100 t4--38 37--56 tn( l l l ) 50--76* 5 1 - 8 0 " 61--87 67-- 9--36 31--49

81 --98" 0--3 0 " 3 0--1 0--2 0 - -3 ' 0--2

33--42 51--59 47--51 93--100 51--58 50--65 0--3 0+-11 0--1 46--55 + 0 - 4 0 - 2 6 0--2 0--3 0--1 59--65* 0 - 3 0--2

70--R9 17--77 72-- 92--100 0--46 13--73" 77--99

0 l 0 - 1 0 - 1 0--2 0 - 2 0 - 2 0 - 2 0 -1 - 0--3 0--3 0 - 3 37--65* 0 3 0--9 l 0 50 68--97 0--17 0--68 0 - 1 0 - 4 0--4: 0--1

5 3 - 7 3 73-- 8:-28 29--53 8 5 - 9 7

0--5 0--3 0--13 0--2

a Mark -. represents weak streak. * Faint spot remains at the start.

360 C h r o m a t o g r a p h i a Vo l . 14 No. 6, June 1981 Or ig ina ls

(a) 1.0

0.5

(b) LO r-

RF

0.5

0

1.0

RF

0.5

1.0

(c)

{ . F ~ , o,~; . . . . }~...

(d)

' tit

"I 0.5

(e) tO

, . , { . . . . . . . .

i i

i

, , . a , , , ~ ; ; o , L

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t { ; . . . . . . { [ t

Be AI Sc V Mn Co Cu Ga As Sr Zr Mo Pd In Sb Ba Sm Hf Re Au Tt Bi U (IV) (if) (II) (if) (If) (V) (Vl) (If) (I~) (if) (VII) (Ill) (I) (I~) (V])

Ca Mg Ti Cr Fe Ni Zn As Se Y Nb Rh Cd Sn Te La Yb W Pt Hq Pb T h

(IV) (Ill) (Ill) (II) (~3 (IV) (V) (111) (IV) (IV) (Ill) (Vl) (IV) (II} (li)

Fig. 1

R F spectra of metal ions chromatographed on Dowex 1 and Dowex 50 layers in mixtures of HOAc - x M HCI, 0 . 1M in T O P O .

a) Dowex 1 , X - 8 H O A c - 6 M H C I ( 1 9 : l ) , O . 1 M i n T O P O d) D o w e x 5 0 , X - 8 H O A c - - 6 M H C I ( 1 9 : 1 ) , 0 . 1 M i n T O P O

b) Dowex 1 , X - 8 H O A c - - 1 M H C I ( 1 9 : l ) , 0 . t M i n T O P O e) D o w e x 5 0 , X - 8 H O A c - 1 M H C I ( 1 9 : 1 ) , 0 . 1 M i n T O P O

c) Dowex 50, X-8 HOAc - 12M HCI ( 1 9 : 1 ) , 0 . 1 M in T O P O

For the anion-exchange systems involving acetone and methanol again differences in RF values between with and without TOPO media are quoted for Sc(III), Zr(IV), Hf(IV) and Th(IV), but weak spots sometimes remain at start for these elements in both systems.

The cation-exchange behaviour of the same metal ions in organic solvent - 6M HC1 (19:1) and organic solvent - 6M HCI (19:1), 0.1M in TOPO are given in Table lI. TOPO does not have appreciable effect on RF values in methanol medium for most metals. Hf(IV), Mo(VI), Sc(llI), Th(IV) and U(VI) exhibit increased RF values, but the magnitude is not marked. In acetone medium, Hf(IV), Mo(VI),

Sc(llI), Sm(ll l) , Ti(IV) and U(VI) exhibit increased RF values in the presence o f TOPO in accordance with their extractability with TOPO in toluene [ l l ] , mostly giving weak spots over the starting point. Similarly, in acetic acid medium the increase in RI;" values are observed for Hf(IV), Hg(ll), In(Ill), Sc(IIl), Ti(IV), U(VI) and Zn(II). In contiast to the anion-exchange system, metal ions are distributed chromatographically for both acetic acid - 6 M HC1 and acetic acid - 6M HCI - TOPO systems, so that multicomponent separations may be feasible particularly in the latter system. Therefore acetic acid - HC1 - TOPO system was further investigated m o r e in details. Fig. 1

Chromatographia Vo[. 14 No. 6, June 1 9 8 1 Originals 361

(a) (b) (c) (d) 1.0 1,0

.ol,,I v,,v, ~ p;i , u;,I

Fig. 2

Separations

Solvent: H O A c - 1M HCI (19:11,0.1M in TOPO Solvent: HOAc - 6 M HCl (19:1) ,0 .1M in TOPO a: Dowex 50, X-8 layer, b) Dowex 1, X-8 layer, c: Dowex 50, X-8 layer, d: Dowex 1, X-8 laver.

illustrates the R v spectra o f metal ions chromatographed on Dowex 1 and 50 layers in acetic acid - xM HC1 (19:1) media, 0.1 M in TOPO. The hydrochloric acid concentration varied, the concentrations of acetic acid and TOPO being kept constant. In the Dowex 1 system hydrochloric acid concentration affects the Rv values to a lesser extent for most metal ions. The Dowex 1/acetic ac id-(1-6)M HCI, O.1M in TOPO, system appears to allow Sc(Itl) and Th(IV) to be separated selectively from many other ele- ments including the rare earths and U(VI). Ba(II) can also be separated from most metals tested except for Sr(II) particulary in acetic acid - 6M HC1 (19:1) , 0.1 M in TOPO medium. When chromatographed on Dowex 50 layers, many metal ions tend to distribute chromatographically. R F values o f Sc(lI1), Cr(III), Mn(II), Fe(llI), Co(II), Ni(II), Cu(II), Zn(II), Ga(III), Cd(ll), In(III), Th(IV) and U(VI) increase with increasing concentration o f hydrochloric acid, while many other ions do not change appreciably their RF values with the concentration o f hydrochloric acid. Again, increas- ed R F values of Zr(IV) and Hf(1V) are noticed, o f which Zr(IV) has been found to have the distribution coefficient of ~ 103 on Dowex 50 in systems 90% acetic acid mix- tures containing 10% of (1.5 to 12M) hydrochloric acid

[121. The Dowex 50 system permits many multielement separa- tions to be conducted, because o f wide distribution of RF values o f elements. Inspection o f RF values will permit the difficult separations to be conducted on both Dowex 1 and Dowex 50 layers. Typical chromatograms involving two, three and four component separations are illustrated in Fig. 2. It took about 4 h to complete the separations.

Thin-layer chromatographic technique is very suited to find the selective or even specific separation system consisting o f organic solvent - acid - complexing agent - ion-ex- change resin, because it provides an easy and prompt inspec- tion of entire developed chromatograms. Information ob- tained will help facilitate the development of column methods.

References

11] Z Korkisch, "Modern Methods for the Separation of Rarer Metal Ions", Pergamon Press, Oxford, 1969.

12] F. W. E. Strelow, in "Ion Exchange and Solvent Extraction", Vol. 5, J.A.Marinsky and Y.Marcus, cds., M. Dekker Inc., New York, 1973, pp. 122-206.

[3] J. Korkisch, Separ. Sci. 1,159 (1966). 141 J. Korkisch and K.A. Orlandini, Anal. Chem. 13, 1952

(1968). 151 J. Korkisch and K. A. Orlandini, Talanta 16, 45 (1969). [61 A.K.De and C.R.Bhattacharyya, Anal. Chem. 44, 1686

(1972). I71 W. Koch and J. Korkisch, Mikrochim. Acta [Wien], 1972,

687; 1973, 101,117, 225,245,263,877. 181 J. Korkisch and W. Koch, ibid. 1973, 865. 19] R. Kuroda, N. Yoshikuni and K. Kawabuchi, J. Chromatogr.

47,453 (1970). I101 R. Kuroda, K. Ogurna and H. Watanabe, J. Chromatogr. 86,

167 (1973). I 111 O.G. Koch and G. A. Koch-Dedic, "Ilandbuch der Spuren-

analyse", Teil 1, Springer-Verlag, Berlin, 1974, p. 290. 1121 J. Korkisch and S. S. Ahluwalia, Talanta 14,155 (1967).

Received: Dec. 17, 1980 Accepted: Jan. 23, 1981 A

362 Chromatographia Vol. 14 No. 6, June 1 9 8 1 Originals