Micellar Electrokinetic Capillary Chromatography of Methylated Flavone Aglycones

Determination of flavonoid aglycones in several food samples by mixed micellar electrokinetic chromatography

The application of mixed micellar electrokinetic chromatography to the separation of ten flavonoid aglycones (catechin, epicatechin, naringenin, morin, fisetin, quercetin, kaempferol, galangin, apigenin, and chrysin) belonging to four different classes (flavanols, flavanones, flavonols, and flavones), and expected to be prominent in commonly consumed foods, has been developed. A micellar system composed of 25 mM SDS and 25 mM sodium cholate buffered at pH 7.0 provided a simultaneous separation of all compounds in less than 20 min. The procedure could be easily adapted to the determination of some flavonoids from each of these classes in real complex samples (propolis, Ginkgo biloba, etc.). The LODs of these compounds were in the range of 1.2-4 microg/mL, and the peak area and migration time repeatabilities were below 6.0 and 3.1%, respectively.

Investigation of the factors that induce analyte peak splitting in capillary electrophoresis

Peak splitting has a detrimental effect on analyses by capillary electrophoresis. Many papers have reported it and several mechanisms have been proposed to explain the phenomenon. We investigated the electrophoretic behavior of an amphoteric analyte, levodopa, in phosphate buffer and observed a peak splitting phenomenon at moderate sample concentrations and under general analytical conditions, even without organic solvent. The dependence of effective mobility on pH was taken into account and pKa values of 2.30, 8.11, and 9.92 were obtained for levodopa. Then, we constructed pH-dependent distribution diagrams of levodopa and phosphate species present in aqueous solution and proposed that the most relevant factors contributing to peak splitting are the presence of ionizable groups in the analyte molecule and the occurrence of ionization, yielding charged species which interacted with buffer electrolyte species in a definite pH range to form complexes. This result is different from those presented in the literature and broadens our understanding of amphoteric analyte peak splitting.

Capillary electrophoresis of anthraquinones from Cassia siamea

The separation and determination of two anthraquinones, emodin and chrysophanol, and two bianthraquinones, cassiamin A and cassiamin B, were achieved by capillary electrophoresis (CE). The running electrolyte used in this method was 0.05 M hydroxypropyl-gamma-cyclodextrin in 0.1 M borate buffer (pH 9) containing 10% acetonitrile, with an applied voltage of 20 kV. Application of this technique in the determination of the main bianthraquinones, cassiamin A and cassiamin B, of Cassia siamea is demonstrated in this paper.

Capillary electrophoresis of natural products

Capillary electrophoresis (CE) and micellar electrokinetic chromatography were used for the separation of widely different compounds from natural materials including antibiotics, humic substances, flavonoids, isoflavonoids, illicit drugs, coumarins, alkaloids, steroids, Chinese herbal preparations, nicotine, caffeine, amphetamines, toxins such as aflatoxins B1, B2, G1, G2, mycotoxins, heptapeptide toxins and others, ephedrine compounds, mineral elements, and natural compounds in biological samples. A discussion of sample extraction and clean-up and the advantages of using CE is also presented.