Gradient elution capillary electrochromatography and hyphenation with nuclear magnetic resonance

Coupling of gradient capillary electrochromatography (gradient CEC) and cap illary zone electrophoresis (CZE) with nuclear magnetic resonance spectrosc opy (NMR) was performed using a recently developed capillary NMR interface. This technique was applied for the analysis of pharmaceuticals and food. A n analgesic was investigated using isocratic and gradient continuous-flow C EC-NMR. Comparison of the results demonstrated the superiority of gradient CEC over isocratic CEC. Aspartame and caffeine, both ingredients of soft be verages, were separated and analyzed by continuous flow CZE-NMR. The order of elution could be reversed by altering the pH. This reversal led to an in creased sample concentration in the NMR detection cell, thus allowing the a cquisition of a totally correlated spectroscopy (TOCSY) two-dimensional (2- D) spectrum of the synthetic peptide aspartame.