Talk by Peter C. Hauser, University of Basel – Niels Bohr Institute - University of Copenhagen

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Talk by Peter C. Hauser, University of Basel

Capillary electrophoresis with contactless conductivity detection

Capillary electrophoresis (CE) carried out in conventional capillaries or on lab-on-chip devices is a very powerful analytical separation technique.  In contrast to liquid chromatography it requires only relative simple instrumentation.  Besides the inexpensive capillary, all that is basically required are a high voltage power supply and small amounts of buffer solutions.  This makes the method well suited for inexpensive field instrumentation or for the construction of analysers for on-site process analysis or environmental monitoring. 

In order to realise the full potential of the technique, it is however necessary to employ specially developed detection techniques, rather then the standard UV-absorption detectors adopted from HPLC which are the norm for commercial CE-instruments.  The electrochemical detection methods, namely potentiometry, amperometry and conductometry are therefore of prime interest, and in our laboratory in particular contactless conductivity detection (C4D) has been pursued in recent years.  The method allows the facile detection of all charged inorganic as well as organic and biochemical analytes with good sensitivity, including those species which are not accessible by optical means.  The detectors have been thoroughly investigated and a comprehensive understanding of the fundamental properties has been reached.  Commercial devices which have been optimized in accordance to these findings are now available and can be retrofitted to existing instruments. 

A range of projects based on CE-C4D are carried out in our laboratory.  Applications in conventional capillary electrophoresis as well as chip based separations are developed.  These include the separation of cationic and anionic enantiomers, the determination of native inorganic and organic blood electrolytes, the clinical analysis of illicit drugs as well as therapeutic drug monitoring (TDM).  The monitoring of enzymatic reactions is also investigated, including the study of acetylcholinesterase inhibitors, and the electrophoretically mediated microanalysis (EMMA) approach. 

Field portable CE-instruments have been designed and are further refined.  An automated system based on a sequential injection analysis (SIA) mainfold has been developed for unattended monitoring operations in environmental or process analysis.  The system also allows the introduction of a hydrodynamic flow.  This is a useful additional parameter for optimisation of separation and analysis time which can only be made use of when using narrow capillaries in combination with a C4D. 

In order to extend the lower limits of detection of CE-C4D preconcentration techniques such as those based on solid-phase extraction using the SIA-manifold as well as electrodriven membrane extraction techniques are being explored.