Preconcentration by the use of ion-exchangers is superior
in some aspects to that of solvent extraction due
to the difficulties encountered in the treatment of large
volumes of the analyte solution, delay in attaining equi-
∗ Corresponding author.
E-mail address: rapak@istanbul.edu.tr (R. Apak).
librium, the mutual solubility of the two phases in one
another, emulsion and third-phase formation and losses in
selectivity of extraction procedures. Moreover, if the distribution
coefficient of the analyte is not sufficiently high,
multistage extraction may be necessary, requiring a large
number of theoretical extraction plates. On the other hand,
in the last 20 years, the use of ion-exchangers for metal
ion preconcentration and the separation has considerably
increased. The basic advantages of such an application lie
in the increased selectivity, high preconcentration factors,
higher degree of adsorbent–adsorbate interaction, mechanical
stability of the resin, repetitive use over many cycles
of adsorption–elution–regeneration, and reproducibility of
analytical preconcentration and determination. Aside from
some natural and synthetic materials such as silica, carbon,
and cellulose subjected to physical and chemical treatment,
the functional groups that find use in potentially important
resins are iminodiacetate (e.g. Chelex-100) and hydroxyquinoline
on styrene-divinylbenzene copolymers and
polystyrene polymers, poly(acrylamino phosphonodithiocarbamates),
poly(dithiocarbamate) resins and Amberlite copolymers functionalized with various organo-analytical
reagents [4]. Transition and rare earth elements were preconcentrated
and separated from alkali, and alkaline earth
metals and matrix components such as seawater samples
by coupling a chelating column, a cross-linked iminodiacetate
chelating resin, with a preconcentrator column,
a high capacity sulfonated polystyrene-divinylbenzene
cation-exchange resin to achieve detection limits of the
order of nanograms [5]. Modern ion chromatography (IC)
represents the evolution of ion-exchange chromatography
based on more sophisticated mechanisms of separation from
complex matrices [6].