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A pressurized CEC (pCEC) method with gradient elution was developed for the analysis of flavonoids in two genetically modified corns and five nongenetically modified corns. The pCEC separation of flavonoids was performed on a monolithic silica-ODS column with UV detection at 270 nm. The effects of the concentration of organic solvent in the mobile phase, pH of the electrolyte buffer, applied voltage, and the gradient elution conditions were evaluated systematically. Gradient elution mode was used as an online concentration method to improve the detection sensitivity of flavonoids. Compared to the conventional injection (0.2 muL), there were 9- to 20-fold improvements in the detection sensitivity at the injection volume of 5 muL without adverse effect on the band broadening and the separation resolution. The LODs for the six flavonoids were in the range of 6.5-46 ng/mL under the gradient elution conditions. The developed gradient pCEC method was applied to evaluate flavonoids in various types of corns. The contents of flavonoids in genetically modified corns and nongenetically modified corns were compared.

A pressurized CEC (pCEC) method was developed for the separation of phytohormones, in which UV absorbance was used as the detector and a monolithic silica-ODS column as the separation column. The parameters (including the concentration of organic solvent in the mobile phase, pH of the electrolyte buffer, applied voltage) affecting the separation resolution were evaluated. Two on-line concentration techniques, namely, solvent gradient zone sharpening effect and field-enhanced sample stacking, were utilized to improve detection sensitivity. The combination of the two techniques proved to be beneficial to enhance the detection sensitivity by enabling the injection of large volumes of samples. Compared to the conventional injection mode, the enhancement in the detection sensitivities of phytohormones using the on-line concentration technique is in the range from 9- to 23-fold. The developed pCEC method was applied to evaluate phytohormones in corns.

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