On-line Study of Aesculin and Aesculetin Hydrolysis Using Sweeping-Flow Injection-chip Micellar Electrokinetic Chromatography

Abstract

Aesculin and aesculetin hydrolysis were studied on-line using sweeping-flow injection-chip micellar electrokinetic chromatography (Sweeping-FI-chip MEKC). With this method, all the analytes in the sample are well separated within 5 min, and a sampling rate of 12 per hour is achieved. At this sampling frequency, a rate constant can be obtained within 30 min. In contrast to off-line methods, it was quite time. saving. And the aesculin hydrolysis mixture solution is directly injected and analyzed without quenching the reaction, thus the information of the hydrolysis process can be obtained from the electrophorogram of a sequence injection. Under the optimum conditions, the hydrolysis rate constants for aesculin at 25, 30, 35, 40 and 45 degrees C using 0. 1 mol/L KOH as hydrolyte are obtained as 3. 65 x 10(-2) /min, 5. 24 x 10(-2) /min, 7. 12 x 10(-2) /min, 10. 5 x 10(-2) /min and 16. 3 x 10(-2) /min, respectively. The activation energy for aesculin hydrolysis is 58. 57 kJ/mol. The hydrolysis rate constants for aesculetin at 15, 20, 25, 30 and 35. using 10 mmol/L KOH as hydrolyte are obtained as 2. 26 x 10(-2) /min, 2. 85 x 10(-2) /min, 3. 55 x 10(-2) /min, 4. 38 x 10(-2) /min and 5. 29 x 10(-2) /min, respectively. The activation energy for aesculin hydrolysis is 31. 55 kJ/mol.