Use of an HPLC photodiode‐array detector in a study of the nature of a black tea liquor

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Abstract
The non‐volatile, water‐soluble constituents of black tea were studied by using reversed‐phase HPLC with a photodiode‐array detector, using a linear gradient developed for this purpose. The data generated by this detector from one injection of a black tea liquor allowed information on the nature and purity of the constituents to be obtained. The following constituents were identified by the spectral data and the retention times given by reference compounds: caffeine, theobromine, (−)‐epicatechin gallate, (−)‐ epigallocatechin gallate, gallic acid, chlorogenic acid (5‐O‐caffeoylquinic acid), p‐coumaroylquinic acid, quercetin 3‐glucoside, quercetin 3‐rhamnosylglucoside, kaempferol 3‐rhamnosylglucoside, and theaflavin digallate. Other peaks were classified by spectral data, but without reference compounds conclusive assignments could not be made. Finally, a group of peaks could be classified as coloured phenolic pigments, and tentatively assigned as thearubigins.