Liquid Chromatography in Migration Studies
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LIQUID CHROMATOGRAPHY IN MIGRATION STUDIES
LARS CARLSEN and WALTHER BATSBERG Chemistry Department, Ris0 National Laboratory, DK-4000 Roskilde, Denmark
INTRODUCTION A detailed knowledge of the geochemical environment of a site for the disposal of radioactive waste is
of fundamental importance.
behaviour of radionuclides in
To evaluate the migration
geological media a series of data are needed,
amongst others a number of physico-chemical properties of the media, permeability,
porosity,
dispersion-, diffusion-,
such as
and sorption characteristics.
In this connection liquid chromatography appears to be advantageous as a facile experimental technique to obtain relevant data for these physico-chemical properties. The capabilities of the liquid chromatography technique in connection with migration studies are in
the following illustrated by examples from recent stud-
ies on the cretaceous formation overlying the Erslev salt dome Denmark). 1,2
(North Jutland,
BASIC PRINCIPLES OF THE LIQUID CHROMATOGRAPHY TECHNIQUE Liquid chromatography is
a column technique normally used for the separation
of different organic as well as inorganic components in a solution. A typical experimental set-up for a liquid chromatographic separation is shown in
figure 1. The pump delivers a solvent (eluent) flow at a preset, con-
stant flow rate. Samples of known volume are injected into the column via the injection port and the eluate from the column is
continuously monitored by a de-
tector. For a given column material,
e.g. chalk,
the separation mechanism will be
controlled by the physical and chemical nature of the interaction between the molecules present in partition-, nation,
the injected sample and the column material.
substitution-,
and ion exchange processes,
can occur in the columns,
chromatogram.
Adsorption-,
separately or in
combi-
being responsible for the actual shape of the
Figure 2 depicts a typical chromatogram used for the determination
of the different physico-chemical characteristics of the columns. The shape of the peak corresponding to an unretarded solute characterizes the flow dispersion in the column (vide infra),
whereas the elution volume (or time)
716 as well as the shape for a retarded peak characterizes sorption phenomena, ted to the solute under investigation, on the column packing material. cal peak shapes are normally obtained in
cases where a single mechanism,
concentration independent distribution coefficient, phenomena.
rela-
Symmetriwith a
can describe the sorption
Cases where several mechanisms are operating simultaneously will gen-
erally lead to skewed peaks.
ELUENT RESERVOIR
PUMP
INJECTION PORT I--PORT
COLUMN
DETECTOR
I RECORDER WASTE Fig.
1. Experimental Liquid Chromatography set-up
UNRETARDED SOLUTE INJECTION OF SAMPLE
RETARDED SOLUTE
Vo to
V=O t 0
VR VOLUME tR TIME
Fig. 2. Schematic Chromatogram defining elution volume and time. Permeability. The permeability, volume flow rate, Q (cm 3/sec), (m),
K, for a given column is
through the column
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