DETECTION OF PHENOLIC-ACIDS IN BEVERAGES BY CAPILLARY-ELECTROPHORESISWITH ELECTROCHEMICAL DETECTION

Capillary electrophoresis using amperometric detection is used to dete ct phenolic acids in beer samples. Both the detection and injection co nditions were optimized. First, the electrophoretic separation require s that the phenolic acids be charged and therefore the pH be above the ir pK(a)s, However, electrochemical detection is optimal when the pH i s low so that the phenolic acids are neutral and not repulsed by negat ive charges on the electrode surface. These divergent conditions were met by using a pH 7.2 run buffer and lowering the pH after the separat ion by using nitric acid in the detection reservoir. Cationic and neut ral compounds in the beer samples interfered with electrochemical dete ction by passivating the electrode surface. These compounds were remov ed using a reversed-polarity injection technique to elute them from th e separation capillary into the sample reservoir prior to the electrop horetic separation. These techniques were demonstrated by detecting se veral phenolic acids in various types of beer. Electrophoretic peaks i n the samples were identified by both matching their elution time and electrochemical properties with standards. The use of voltammetric cha racterization provided improved peak identification for complex sample s.