Comparison of nano and conventional liquid chromatographic methods for the separation of (+)-catechin-ethyl-malvidin-3-glucoside diastereoisomers.

Nano-liquid chromatography and conventional HPLC were used for the separation of diastereomers of (+)-catechin-ethyl-malvidin-3-glucoside. Those bridged anthocyanin dyes were obtained by reaction of (+)-catechin with malvidin-3-glucoside in the presence of acetaldehyde. Both diastereomers were isolated with semipreparative chromatography and their structures were confirmed by nuclear mag- netic resonance and mass spectrometry. In-laboratory prepared capillary columns packed with fully porous particles Chromosphere C18, dp = 3 microm, core-shell particles Kinetex C18, dp = 2.6 microm (100 microm i.d.)and monolithic column Chromolith CapRod (100 microm i.d.) were used for the separation of (+)-catechin,malvidin-3-glucoside and both diastereomers. Chromosphere C18 stationary phase provided the best chromatographic performance. Mobile phase containing water:acetonitrile (80:20) acidified with tri- fluoroacetic acid (0.1%, v/v/v) was used in an isocratic elution mode with a flow rate of 360 nL min-1. Separation of studied compounds was achieved in less than 7 min under optimized conditions. The nano-liquid chromatographic method and a conventional HPLC one using the same fully porous particles (Chromosphere C18, 3 microm, 100 mm × 4.6 mm) were compared providing higher separation efficiency with the first analytical method and similar selectivity. A better peak symmetry and higher resolution of the studied diastereomers was achieved by conventional chromatography. Nevertheless, nano-liquid chromatography appeared to be useful for the separation of complex anthocyanin dyes and can be uti- lized for their analysis in plant and food micro-samples. The developed method was used for analysis of red wine grape pomace.