Capital HPLC

Electrochromatography - CEC

ELECTROCHROMATOGRAPHY - CEC

As an alternative to the use of hydraulicpressure, chromatographic mobile phases can
be made to flow through a chromatographic column by the application of an electric field.
As in capillary electrophoresis, this must be carried out in narrow bore capillaries. Thus,
the instrumental requirements for electrochromatography are similar to those of
free solution capillary electrophoresis.

In CE it is often the case that the differences
in electrophoretic mobilities of closely related chemical species are extremely small and as
a result sufficient resolution may not be achieved despite the very high plate number.
However, the use of packed capillaries introduces an additional separation
mechanism, namely chromatographic partition.
In electrochromatography the selectivity is therefore the result of a superimposition of
electrophoretic and chromatographic migration.
Thus, the various possibilities for modification of selectivities
available to the HPLC user can be employed in electrochromatography.

With packed columns, unlike with open tubes, UV-absorbance detection cannot be carried
out through the capillary, at least not without severe difficulty, due to the presence of the
packing material. In theory, packed columns could be connected to a short length of an
open capillary in which the detection would take place. However, the problems, in terms
of dead volumes etc., which would arise in the joining of capillaries of only 50μm i.d. prohibit
this approach.

Electro-Kinetic Technologies have developed a unique solution to this problem by producing
capillaries with a small retaining frit inside the column positioned several centimetres from
the capillary outlet. After packing the packed bed extends only as far as the retaining frit
which allows detection to be carried out, using conventional capillary electrophoresis
equipment, in the empty zone immediately following the frit. Using this method detection
can be carried out with the absolute minimum extra-column broadening.

EKT Packed Capillaries for Electrochromatography

The diagram below shows the arrangement of the on-column flow cell for Electro-Kinetics
packed capillary columns.

In the case of electro-chromatography the observed chromatographic efficiency, in terms of the number of theoretical plates obtained, is often considerably greater than the same column driven at the same linear flow velocity using pressure induced flow. This is due to the ideal uniform flow characteristics of electroosmotic flow. In electrochromatography there is no direct relationship between the flow velocity and the particle diameter. Thus, the particle diameter can be reduced to well below the particle diameters currently used in HPLC. This leads to chromatographic efficiences approaching those of free solution capillary electrophoresis. See chromatogram below on 1.5μm diameter particles.

EKT Packed Capillaries- Ordering Information

EKT packed capillary columns for electrochromatography are available packed
with any material from our vast range of HPLC packing material. These include: Our own
Inertpak and Optimal, Spherisil, Adsorbosphere, Apex, Chromegabond, Exsil,
Hypersil, Kromasil Lichrosorb, Nucleosil, Partisil, Rosil (or C-Gel), Spherisorb,
Synchropak, Techsphere, YMC and Zorbax.

Please contact us if the material you require is not listed.
The number of combinations of phase, particle size, and type of silica runs into several
thousand. Thus, only a small selection of our range is listed below. When ordering packed
capillary please give a full specification of your requirements with your order.

                              Electrosil 1.5μm Particle Columns

Spherisorb Columns

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Hypersil Columns

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