Conductivity detection cell for capillary zone electrophoresis with a solution mediated contact of the separated constituents with the detection electrodes
R. Bodor et al., Conductivity detection cell for capillary zone electrophoresis with a solution mediated contact of the separated constituents with the detection electrodes, J CHROMAT A, 916(1-2), 2001, pp. 31-40
A contact conductivity detection cell for capillary zone electrophoresis (C
ZE) with an electrolyte solution mediated contact of the separated constitu
ents with the detection electrodes (ESMC cell) was developed in this work.
This new approach to the conductivity sensing in CZE is intended to elimina
te detection disturbances due to electrode reactions and adsorption of the
separated constituents when these are coming into direct contact with the d
etection electrodes, An optimum detection performance of the cell was achie
ved when the carrier electrolyte solution mediated the electric contact of
the detection electrodes with the separated constituents. Different composi
tions of the mediator and carrier electrolyte solutions led to large drifts
of the detection signals. Isotachophoresis experiments performed in this c
ontext with the ESMC cell revealed that origins of these drifts are in tran
sport processes (diffusion and electromigration) between the detection comp
artment and the detection electrodes in the cell. These processes affected,
to some extent, other analytically relevant performance parameters of the
ESMC cell of the present construction as welt [e.g., concentration limits o
f detection (LODs), a contribution of the cell to the band broadening]. For
example, the ESMC cell gave, under optimum operating conditions, 3-4 times
higher concentration LODs for the test analytes than a current on-column c
onductivity cell employed under identical working conditions. On the other
hand, these LOD values (25-150 nmol/l) were still 20-5 times lower than tho
se estimated from reference experiments for a contactless conductivity dete
ctor. CZE experiments with iodide, carried out under working conditions lea
ding to electrochemical reactions of this anion on the detection electrodes
of current conductivity cells, did not occur in the ESMC cell. In addition
, this cell, contrary to a reference contact conductivity cell, required no
special carl (e.g., cleaning of the surfaces of the detection electrodes b
y chemical or electrochemical means) to maintain its reliable long-term per
formance. Anionic CZE analyses of tap and mineral water samples monitored b
y the conductivity detector provided with the ESMC cell demonstrated a prac
tical applicability and certain limitations of this detection approach in t
he analysis of ionic constituents present in high ionic strength sample mat
rices. (C) 2001 Elsevier Science B.V. AII rights reserved.