CDs in electrophoresis

It was 1982, when CDs were first used in isotachophoretic analysis of alkali and alkaline metals, in which as a complexing additive a-CD obviously improved the separation effect. Since that time, many investigations of CDs application in various types of electrophoresis have been carried out. 

In capillary electrophoresis (CE), CDs and their ionic and neutral derivatives have been successfully used as additives in the carrier system for the separation of structural isomers and structurally related compounds [53]. The commonly used neutral CDs are the native a-, /3- and y-CDs and the dimethyl, trimethyl, hydroxyethyl and hydroxypropyl forms [54]. The charged CDs are carboxymethyl, sulfobutyl ether, sulfated and amino CDs. The methyl derivatives of the CD are effective in separating chiral compounds, enantiomers of terbutaline, ephedrine and carnitine. The neutral derivatives of hydroxyalkylated /3-CD and the mixture 

CDs could be used as leading electrolyte additives in isotachophoresis for improving the selectivity [58]. The addition of a-CD in the leading electrolyte contributed to the complete separation of compounds such as nitrite and nitrate ions, cyanate, thiocyanate and selenocyanate ions, chlorate and perchlorate ions. CDs were also successfully used as leading electrolyte additives in the capillary isotachophoretic separation of positional isomers, such as 2-, 3- and 4-amino phenols, 1,2-, 1,3- and 1,4-diaminobenenes, and substituted aromatic sulfonic acids. 

Micellar electrokinetic chromatography (MEKC), a modified CE, enabled the separation of electrically neutral analytes. However, highly hydrophobic compounds including PAHs, corticosteroids, fat-soluble vitamins and polychlorinated biphenyl (PCB) congeners could not be separated by MEKC in electrophoretic medium of sodium dodecylsulfate (SDS) [59]. The use of CDs to the SDS solution can remarkably improve the resolution of analytes. For example, a mixture of water-soluble and fat-soluble vitamin or esterom can be successfully separated by MEKC by the addition of y-CD in the SDS electrophoretic medium [60]. 

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