Preparative Electrochromatography of Tea Polyphenols and Caffeine

A novel low-pressure preparative electrochromatography apparatus was set up to implement the separation of small polar compounds. In this apparatus, a distinguished bottom “T”-shape electrode chamber was designed to remove electrolysis gas and meanwhile enable the apparatus to separate small-molecule solutes. Partial separation of the model sample, crude tea extract (mainly containing (−)-epigallocatechin gallate, (−)-epicatechin gallate and caffeine) by hydrophobic macroporous adsorption column (maximum 40 cm × 20 mm ID) with electric field (maximum 111.0 V cm⁻¹) proved the effectiveness of the electrochromatography apparatus. The fact that the total solute recoveries were over 90% showed the qualification of the apparatus for preparative purpose. The stronger the electric field, the more obvious the electrically induced effects. An alternative in-liquid load manner (loading sample in liquid after the electric field was applied) was proposed, which could further enhance the electrically induced effects than in-column load manner (loading sample on resin bed before applying electric field). Scale-up on electrochromatography by column diameter from 6 to 20 mm resulted in similar electrically induced effects on peak resolutions. All of these investigations revealed that the new technology was feasible and promising on separating small polar compounds, for it inherits the advantages of both liquid chromatography and electrophoresis.