Capillary electrophoresis, dispersion additives

The most common chiral additives used in chiral capillary electrophoresis with micellular solutions (mostly micelles of sodium dodecylsulphate) are derivatives of the three basic cyclodextrins. This system might be considered more of a chromatographic process than one that is electrophoretic, as the solutes are distributed between the aqueous electrolyte phase and the cyclodextrin/micelle phase. The derivatized cyclodextrin additive will also be distributed between the electrolyte and the micelles, the extent of which will depend on the type of derivatized cyclodextrin and its capacity for dispersive or polar interactions with the micelles. As the cyclodextrin additive itself partitions between the electrolyte and the micelle (albeit the distribution under certain circumstances may be small) some of the chiral additive will be distributed on the micelle surface and will act as a chiral stationary phase. 

The zeta potential (Q is thought to be the same as the Stem potential which is defined at the plane dividing the Stem layer and the diffuse layer of the EDL. Zeta potential is an experimentally measurable electrical potential that characterizes the EDL, and it plays an important role in many apphcations such as stability of colloidal dispersion, characterization of biomedical polymers, electrokinetic transport of particles, and capillary electrophoresis, etc. In addition, zeta potentials of the particles and the channel wall are cmcial to the design and process control of microfluidic devices. A review on measuring the zeta potential of microfluidic substrates was provided by Kirby and Hasselbrink [3]. 

As the initially injected sartple plug is normally a distance away from the capillary inlet in capillary electrophoresis, the entrance region should have negligible influence on the species transport. In the region of fully developed (denoted by the subscript fd) flow field, the thermally induced pressure-driven flow causes additional hydrodynamic dispersion to the species diffusion. Analogous to Eq. (17), the effective dispersion coefficient is given by... 

The combination of XRF with electrophoresis can constitute a quasi-on-line coupling technique. Great efforts have been made to develop on-line analysis techniques with XRF. Mann et reported a technique of on-line SRXRF detection of metal ions, such as Fe, Co, Cu, and Zn, in their high binding-constant complexes for capillary electrophoresis (CE) separation. An X-ray transparent polymer coupling is used to create a window for the on-line X-ray detection. In contrast to ICP-MS, this detection technique is not limited by sample or the buffer volatility or atomization efficiency. Simultaneous XRF and UV absorbance detection can be used to provide on-line determination of metal/chelate ratios. A bench-top energy-dispersive micro X-ray fluorescence system was also combined with the CE apparatus constructed by a thin-walled fused-silica capillary for elemental analysis of the species containing Fe, Co, and Cu, for example. This coupled technique used for metalloprotein speciation analysis can avoid the compromise between optimal separation and sensitive detection, which must be taken into account in the HPLC-ICP-MS procedure. In addition, this detection scheme is non-destructive, so the separated material can be recovered for additional characterization. 

Electrokinetic chromatography (EKC), or electrokinetic capillary chromatography (ECC) — An electrophoretic separation technique (- electrophoresis) based on a combination of - electrophoresis and interactions of the analytes with additives (e.g., - surfactants), which form a dispersed phase moving at a different velocity. In order to be separated either the analytes or this secondary phase should be charged. 

---