annual report annual report annual report annual report 2005

80
RADIOCHEMISTRY, STABLE ISOTOPES,
NUCLEAR ANALYTICAL METHODS, GENERAL CHEMISTRY
Fig.2. Van’t Hoff plots of: a) Sc 3+ , Lu 3+ , Yb 3+ , Tm 3+ , Er 3+ , Ho 3+ , Y 3+ , Dy 3+ and Tb 3+ (Column – Ion Pac CS3+CG3,
eluent – 80 mmol·L –1 α-HIBA, flow rate – 1 mL·min –1 , temperature range – 10-65 o C. Sample: Sc 3+ – 5 mg·L –1 ; Lu 3+ ,
Yb 3+ , Tm 3+ and Y 3+ – 10 mg·L –1 ; Er 3+ and Ho 3+ – 20 mg·L –1 ; Dy 3+ – 30 mg·L –1 ; Tb 3+ – 40 mg·L –1 .). b) Eu 3+ , Sm 3+ ,
Nd 3+ , Pr 3+ , Ce 3+ and La 3+ (Column – Ion Pac CS3+CG3, eluent – 220 mmol·L –1 α-HIBA, flow rate – 1 mL·min –1 ,
temperature range – 10-65 o C. Sample: Eu 3+ – 10 mg·L –1 ; Sm 3+ , Nd 3+ and Pr 3+ – 20 mg·L –1 ; Ce 3+ – 40 mg·L –1 ; La 3+
– 50 mg·L –1 .).
thanum (eluent 220 mmol·L –1 α-HIBA). Gadolinium
was not included because of its interference
with europium under these conditions. Ion Pac
CS3 column with Ion Pac CG3 guard were used in
the experiments. Details concerning the elution
method were published previously [1,2]. Chromatograms
were obtained in all experiments as a function
of column temperature in the range 10-65 o C
when separating the cations in isocratic elution
mode and in the range 10-70 o C when gradient elution
was used. As examples, separations of heavy
lanthanides, scandium and yttrium as well as light
lanthanides at 35 o C are shown in Fig.1. The increase
of the temperature from 10 up to 65 o C caused a
significant increase in retention factors of all REEs
studied including scandium and yttrium. The relationship
between ln k of REEs and inverse absolute
temperature (van’t Hoff plots) is shown in
Fig.2. As one can see from the plots, the overall
ion exchange-complexation revealed endothermic
character for all REEs investigated. The changes
of enthalpy (∆H) given by the van’t Hoff isochore:
dln
k
∆ H =−R (1)
d (1/ T )
where: T – absolute temperature, R – gas constant
(1.987 cal·K –1·mol–1 ), are clearly not constant for
several elements, particularly scandium, yttrium,
praseodymium, neodymium and europium but are
a function of temperature, i.e.:
∆H = ∆H 0 + ∆C p T (2)
where: ∆C p
is heat capacity.
For the other REEs, changes of enthalpy is constant
or almost constant in the temperature range
studied. The relationship between changes of enthalpy
and ionic radius of heavy REE at 5 o C is presented
in Fig.3. The relationship between changes
of enthalpy and ionic radius for heavy lanthanides
is represented by a smooth curve with yttrium lying
distinctly below it.
Values of plate height (H), determined from
isocratic runs at 35 o C are shown as a function of
Fig.3. Enthalpy changes derived from van’t Hoff isochore
for the process of elution of REE from an Ion Pac
CS3 column at 5 o C for Lu 3+ , Yb 3+ , Tm 3+ , Er 3+ , Ho 3+ ,
Y 3+ , Dy 3+ and Tb 3+ . Eluent – 80 mmol·L –1 α-HIBA,
flow rate – 1 mL·min –1 . Sample: Lu 3+ , Yb 3+ , Tm 3+
and Y 3+ – 10 mg·L –1 ; Er 3+ and Ho 3+ – 20 mg·L –1 ; Dy 3+
– 30 mg·L –1 ; Tb 3+ – 40 mg·L –1 as a function of ionic
radius of REE.
reciprocal of the weight distribution coefficient
(1/λ) for heavy (Fig.4a) and light (Fig.4b) REEs.