Unexpected hyperchromic interactions during the chromatography of theafulvins and simple flavonoids

Theafulvins, isolated from black tea, chromatograph as a hump on reversed phase column packings. When whole black-tea brews are similarly analysed other phenolic compounds appear as more or less resolved peaks ‘floating’ on this hump. Model solutions of isolated theafulvins containing individual pure compounds (flavanols, flavonols and caffeine) have been prepared and their chromatographic behaviour compared with that of the pure compound chromatographed alone. In the case of quercetin, epicatechin and epicatechin gallate, a statistically significant hyperchromic effect has been observed in which the peak area ‘floating’ on top of the theafulvin hump is larger than expected from the area obtained for the pure compound alone. There was little or no effect with catechin and caffeine, and rutin showed a weak and inconsistent response. The data are discussed by reference to the established literature on copigmentation but it is not possible to define the mechanism responsible for the hyperchromism at this stage.