Simultaneous Separation of Eight Lignans in Forsythia suspensa by β-Cyclodextrin-Modified Capillary Zone Electrophoresis

Abstract

The aim of the study was to develop an alternative capillary zone electrophoresis (CZE) for simultaneous determination of phillyrin (1), phillygenin (2), epipinoresinol-4-O-β-glucoside (3), pinoresinol-4-O-β-glucoside (4), lariciresinol (5), pinoresinol (6), isolariciresinol (7) and vladinol D (8) in Forsythia suspensa. The structural types of lignans 1–8 could be attributed to bisepoxylignans (1–4 and 6), monoepoxylignans (5 and 8) and cyclolignan (7). The major difficulties in the CZE separation of 1–8 could be summarization as the simultaneous presence of free lignans (1, 2 and 5–8) and lignan glucosides (3 and 4) and simultaneous occurrence of two pairs of isomers (3 and 4 as well as 5 and 7). Without the addition of β-CD and methanol, the resolution of these analytes was quite poor. However, in this study, compounds 1–8 were excellently separated from each other within 15 min under optimized conditions with a borax running buffer (40 mM borax, pH 10.30) containing 2 mM β-CD and 5% methanol (v/v) at the voltage of 20 kV, temperature of 35 °C and detection wavelength of 234 nm. Validation of the method included tests of linearity, precision, repeatability, stability and accuracy. In addition, the method offered inherent advantages such as lower analytical cost, no need of specific columns and use of small amounts of organic solvents and reagents. Finally, this green and economic CZE was successfully applied for the determination of these bioactive components 1–8 in F. suspensa fruits and its commercial extracts.