Capillary Electrophoresis with Conductivity Detection
 - An Alternative to Ion Chromatography?

Capillary Eectrophoresis (CE) is a relatively new familiy of separation techniques which are really worth the name "High Performance Separations" with respect to their remarkable separation efficiency. The methods are based on the principles electrophoretic migration of charged species as well introduced in the methods of slab electrophoresis. 

Electrophoretic separation within a narrow bore capillary enables us to run experiments without a gel or paper. Such a matrix is necessary in slab techniques to prevent convective processes rule or disturb the substance flow but always cause a more or less important interaction of the analyte species with the enormous surface of the matrix.

Within the open capillary system electroosmotic flow (EOF) becomes a regular aid in moving analyte species through the capillary system whereas this phenomenon is just unwanted interaction in classical slab techniques. This basic technique is called Capillary (Free) Zone Electrophoresis (CZE).

All classical electrophoretic techniques have been realized within capillaries then and gain some improvement in control and speed. Besides that special method development led to the powerful Micellar ElectroKinetic (Capillary) Chromatography (MEKC or MECC) and to Capillary ElectroChromatography (CEC) which cover a field of application nowadays ruled by HPLC.

As in the early days of HPLC the question of detection seems to be a center of improvement. The UV-vis diode array detector is state of the art and some approaches have successfully improved its sensitivity (bubble cell, Z-cell). Almost any kind of detector applied to HPLC have been reported for CE but not all of them have been made commercially available yet.

In 1995 ATI-Unicam introduced a conductivity detector module for CE. Prior to that non absorbing ions could only be detected by indirect UV which restricted buffer selection according to detection needs.

A CE-instrument equipped with a conductivity detector seems to cover the application area of Ion Chromatography (IC). Therefore the system was introduced as Capillary Ion Electrophoresis (CIE). The benefits of CIE versus IC have to be discussed in detail with regard to the sample material and concentration range. Generally the CE solution is the more robust and faster technique but may be less sensitive than IC.

Cunductivity detection is generally applicable to the identification of charged molecules and complexes as conductivity is a common property related to ionic mobility. 

In the Microanalytical Laboratory CE has been introduced for ion analysis in summer 1995.

Some application examples have been presented as a poster (sorry, link to a German only page) on January 22^nd 1997 at the "14^th hp-Forum Analytik" at Hewlett-Packard/Vienna/Austria.

At the moment (July 1997) we are members in an inofficial ring experiment on "Analysis of Small Ions by Capillary Electrophoresis and Isotachophoresis" by University Linz/Institute of Chemistry/Department of Analytical Chemistry