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RADIOCHEMISTRY, STABLE ISOTOPES,
NUCLEAR ANALYTICAL METHODS, GENERAL CHEMISTRY
INDIUM ISOTOPE EFFECT IN THE Dowex 50-X8/HCl SYSTEM
– COMPARISON WITH THE ISOTOPE EFFECT OF GALLIUM
Wojciech Dembiński, Irena Herdzik, Witold Skwara, Ewa Bulska 1/ , Irena A. Wysocka 1/
1/
Faculty of Chemistry, Warsaw University, Poland
77
In the framework of our studies on the fractionation
of gallium, indium and thallium by chemical
methods the indium isotope effect ( 113/115 In) has
been discovered in the chromatographic system:
strong cation exchanger/HCl.
Previously, we observed the gallium isotope
effect ( 69/71 Ga) in a similar system. The fractionation
of heavy isotope into the resin phase and the
lighter isotope into the complexes in the solution
was revealed. The value of unit separation factor
for gallium was found to be ε=(2÷3)x10 –5 in the
acid concentration range 1.5÷3.0 M [1,2].
For the separation of indium isotopes, the same
experimental method as for gallium was applied.
It was the merry-go-round elution of the band from
a column 100 cm high and 0.5 cm in inner diameter,
filled with Dowex 50-X8, 200-400 mesh. The
flow rate of effluent (HCl) was 0.11 ml/min. The
only significant difference was that the concentration
of acid was decreased to 0.5 M in order to maintain
the value of K d ≈4. For gallium, as follows from
Fig.1, the same value of K d was reached at 2.5 M
HCl.
The indium content in the consecutive fractions
was followed qualitatively by spot tests with Rhodamine
B [3], and then determined quantitatively
by atomic absorption analysis with flame atomisation.
The ratio (R) of the isotopes, 113/115 In, in selected
fractions was determined by an inductively-coupled-
-plasma mass spectrometer (ICP-MS) Perkin Elmer
Elan 6000. Prior to the analysis, chlorides were removed
from the samples by evaporation with 4 M
HNO 3 to dryness and dissolving the residue in 0.1
M HNO 3 . The relative standard deviation of measurements
was usually 0.05%.
The local separation factors defined as q i =R i /
R feed or the local separation gain defined as ε i =ln(q i )
were calculated from the data.
Fig.2. Local isotope separation gain of indium (N=10 000)
and gallium (N=3200) vs. eluted fraction.
Fig.2, together with the data for gallium taken from
our previous work [2]. The opposite slopes of the
S-shape curves demonstrate the opposite turn of
indium and gallium isotope effects. In fact, the light
isotope of indium was fractionated into the resin
phase, whereas the heavy isotope into the complexes
in the solution.
The unit separation factor was calculated by the
Glueckauf approximation, under the assumption
that the shape of the eluted band resembles the
normal distribution [4,5]. According to this theory
ε is equal to S/N 0.5 , where S is the slope of linear
function of ε i vs. the eluted fraction (∆n/n) at X-axis
scaled in standardized differences (Z) of normal
distribution (Fig.3) and N is the number of theoretical
plates. The same result could be obtained
by plotting ε against ∆n/n on a probability graph
paper.
Fig.3. Local isotope separation gain of indium and gallium
vs. eluted fraction. X-axis in Z units.
Fig.1. K d of indium and gallium vs. acid concentration in
Dowex 50-X8/HCl system.
The results of the indium separation experiments,
performed with 0.5 M HCl, are shown in
The value of unit separation factor for indium
was found to be ε=-2.0x10 –4 , that is one order of
magnitude higher than that for gallium, but of opposite
sign.
The opposite signs of isotope effects reflect the
difference in the stability constants of the complex
species involved in the Me/HCl system. These are