1. Created with MindGenius Business 2005® Capillary Electrophoresis Capillary Electrophoresis Advantages Only needs nL sample High speed and resolution, virtually no band broadening Instrumentation Capillary tube (10 - 100mM internal diam., 40-100cm long) Two buffer reservoirs, with platinum electrodes DC potential (20-30 kV) applied along capillary Sample introduced one end, detector at other Direct of potential depends on charge (+/-) of analyte Separation of analyte ions via differential migration in an electric field, coupled with electro-osmotic flow of mobile phase

2. Created with MindGenius Business 2005® Capillary Electrophoresis Capillary Electrophoresis Mobile Phase Commonly phosphate or borate buffer (20-100 mM) pH and Ionic strength must be controlled Can add detergents to transport neutral molecules in a micelle (MEKC) Stationary Phase No stationary phase for true CE Newer developments introducing a stationary phase combine CE and HPLC to give electrochromatography Principles of separation Based on interaction of analyte with electric field Migration velocity v = (µ e + µ eo ) E where µe and µ eo are the electrophoretic mobilities of the analyte and buffer, and E is the applied field strength

3. Created with MindGenius Business 2005® Capillary Electrophoresis Capillary Electrophoresis Retention and Resolution: dependent on Charge / size ratio is primary separation factor Charge  gives v  and thus RT  Size  gives v  and thus RT  Interaction with buffer ions / molecules pH and ionic strength of buffer affects ionisation of analyte – and thus RT Applied field Column Length Diffusion Optimisation: may involve buffer pH - alter charge status of analyte buffer ionic strength - change capacity to produce electro-osmotic flow organic modifiers: influence ionic strength, and can “capture” analytes selectively to affect charge/size ratio

4. Created with MindGenius Business 2005® Capillary Electrophoresis Capillary Electrophoresis Detection: normally similar to LC detectors but Peak area is dependent on rate of movement through the detector Peak area not independent of retention time Mostly “on-column”, i.e. capillary forms flow cell Short path length gives reduced sensitivity Indirect methods may be needed to increase sensitivity Applications There are a variety of named techniques, each suitable for different analytical problems. You may see mentioned: Capillary zone electrophoresis Capillary gel electrophoresis Capillary isotachophoresis Capillary isoelectric focusing Capillary electrochromatography Micellar electrokinetic capillary chromatography