Simultaneous separation of anionic, cationic, and neutral components in capillary liquid chromatography using...

A simultaneous separation of anionic, cationic, and neutral compounds was carried out in capillary LC using a mixed-bed column of zwitterionic hydrophilic and anion-exchange stationary phases. The combination in stationary phases was suitable to retain anionic, cationic, and neutral analytes. The retentions of anionic compounds were suppressed with the increase in the buffer concentration in the mobile phase whereas those for the cationic and neutral compounds were almost constant, i.e., the anionic analytes were mainly retained by anion-exchange mode and the other compounds by the hydrophilic interaction. Both hydrophilic and electrostatic retentions were successfully controlled by the ACN content in the mobile phase. The gradient elution of increasing water content in the mobile phase achieved good separation for eight compounds found in metabolome analysis within 6 min. Both intra- (n = 7) and inter-day (n = 3) precisions (%RSD) of elution time for every eight compounds were less than 3 and 5%, respectively.