Catechins MEKC analysis

Gotti R, Furlanetto S, Lanteri S, Ohno S, Ragaini A, Cavrini V (2009) Diffaentiation of green tea samples by chiral CD-MEKC analysis of catechins content. ElectrophOTesis 30 2922-2930. doi 10.1002/elps.200800795... 

Capillary electrophoresis (CE) is an emerging analytical technique for determination of catechins. The majority of CE studies involve the analysis of catechins in tea infusion, extracts as well as supplements. The three variants of CE suitable for the analysis of catechins include capillary zone electrophoresis (CZE), micellar electro-kinetic chromatography (MEKC), and microemulsion electrokinetic chromatography (MEEKC) with UV detection. In general, the resolution of MEKC was found to be superior to CZE for separation of catechins. MEEKC is a relatively new technique, and the few reports available suggest that it offers a performance similar to MEKC. CE conditions are often quite complex, and many factors, such as buffer composition, pH, presence of surfactants, and column temperature, can all affect the quality of separation and should be optimized individually. On the other hand, CE offers several advantages over HPLC. The short analysis time (<20 minutes), low running costs, and reduced use of solvents make it an attractive alternative for routine analysis of catechins. 

Recently, MEEKC has been applied for the determination of catechins. In a similar fashion to MEKC, MEEKC uses a pseudo-stationary phase for separation of analytes. Instead of having micelles, surfactant-stabilized oil droplets in microemulsion solution serve as the pseudo-stationary phase for the partitioning of analytes. The formation of a microemulsion involves an organic solvent, SDS as a surfactant, and an alcohol as a cosurfactant. Pomponio et al. first developed a MEEKC method for the analysis of six catechins (C, EC, GC, ECG, EGC, and EGCG). This involved the use of heptane (1.36%, w/v), SDS (2.31%, w/v), and 1-butanol (9.72%, w/v), which serve, respectively, for the three functions mentioned above. The medium was a 50-mM phosphate buffer (86.61%, w/v) at pH 2.5. Electro-osmotic force (EOF) was almost absent, and analytes, due to their interactions with SDS-coated oil droplets. 

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