Off-line comprehensive two-dimensional hydrophilic interaction x reversed phase liquid chromatographic analysis of green tea phenolics.

The separation of green tea phenolic compounds by comprehensive 2-D LC (LCxLC) has been studied. An off-line LCxLC system was designed based on hydrophilic interaction chromatography in the first dimension and gradient RP-LC using a C18 column in the second dimension, to separate compounds based on polarity and hydrophobicity, respectively. Green tea was found to contain a complex composition of low molecular weight phenolic compounds, identified by fluorescence, diode-array and negative ESI-MS detection systems. The LCxLC system was characterized by a very high practical peak capacity (>2100, in approximately 22.5 h) due to the low degree of correlation (r(2)<0.2) between the selected separation mechanisms. The proposed methodology demonstrated its suitability for the analysis of various groups of phenolic compounds including proanthocyanidins, phenolic acids, flavonols and flavonol derivatives, all of which cannot be separated in a single analysis by conventional 1-D HPLC methods.