Hyphenated chromatographic techniques for the rapid screening and identification of antioxidants in methanolic extracts of pharmaceutically used plants

Phytochemical analysis is an important scientific research area, which normally relies on a number of rather laborious and time-consuming techniques for compound identification. Isolation of the ingredients of plant extracts in adequate quantities for spectral and biological analysis was the basis of this research. In this paper the possibility of on-line rapid screening of antioxidant components in methanolic plant extracts and their subsequent identification is reported. Based exclusively on hyphenated chromatographic techniques the methanolic extracts of Tilia europea, Urtica dioica, Lonicera periclymenum and Hypericum perforatum are initially screened for their antioxidant components via an on-line DPPH and ABTS radical scavenging technique. Structural elucidation of the active analytes is achieved by means of LC–MS and LC–UV–SPE–NMR. After the determination of the appropriate LC gradient, a minimal number of chromatographic runs with these hyphenated techniques are adequate for the acquisition of the necessary data, leading to the identification of the targeted compounds. Based on their UV, NMR and MS spectra, the antioxidant compounds identified in the extracts under study were found to be either flavonoid glycosides or mono- and dicaffeoylquinic acids. Although the aim of the study was to show the great potential of the LC–UV–NMR–DPPH/ABTS approach for the rapid screening and identification of plant constituents, the results produced in the course of this study also have some merit by themselves. Some of the compounds detected are reported for the first time in the specific plant extracts.