Three-channel column-switching high-performance liquid chromatography with electrochemical detection for determining...

Three-channel column-switching high-performance liquid chromatography with electrochemical detection (3LC-3ED), which consists of three flow ways, two switching valves, four columns, and three electrochemical detectors, was developed for determining various redox components in Salvia miltiorrhiza with high sensitivity. In this study, the analytes were divided into three groups as follow: Group I [salvianic acid A (Danshensu) sodium salt (DSS), protocatechuic acid (PA), protocatechuic aldehyde (PAD), and caffeic acid (CA)], Group II [rosmarinic acid (RA), lithospermic acid (LA), and salvianolic acid B (SAB)], and Group III [cryptotanshinone (Cry), tanshinone I (Tan I), and tanshinone IIA (Tan IIA)]. By rotating each switching valve to change the elute flow way, the components in Groups I, II, and III were directed into the oxidative (+0.7 V), another oxidative (+0.7 V), and reductive (-0.2V) detection channels, respectively. Chromatographic peaks of components in Groups I, II, and III appeared within 69, 53, and 60 min, respectively, in each channel. The detection limits of DSS, PA, PAD, CA, RA, LA, SAB, Cry, Tan I, and Tan IIA were 4.2, 2.8, 10, 10, 3.9, 3.8, 3.0, 132, 119, and 109 fmol, respectively, thus the sensitivity by the present 3LC-3ED is superior to those of previously reported gradient LC-ED and LC with UV detection. As an application, the phenolic acid contents and tanshinones in nine batches of S. miltiorrhiza were successfully determined.