THE STABILITY OF THEAFLAVINS DURING HPLC ANALYSIS OF A DECAFFEINATED AQUEOUS TEA EXTRACT

It has been shown that the theaflavins and thearubigin hump of decaffe inated aqueous extracts of black tea remain virtually stable for up to 850 min, thus permitting their automated overnight analysis. Within-r un coefficients of variation for the total chromatogram area and peak area for each of the major theaflavins, following repeated (up to 10 t imes) injections of a single extract, did not exceed 2.5 and 6.0%, res pectively. The corresponding values obtained by pooling data obtained on three separate occasions were 3.0 and 7.3%, respectively. Trend-lin e analysis indicated that there was a tendency for each of the areas s tudied to decline by factors in the range 0.11-0.53% of the original v alue per injection. This factor was not statistically significant for theaflavin-3,3'-digallate but reached 5% significance for theaflavin a nd total chromatogram area and 1% for both theaflavin monogallates. Th e magnitude of these changes is too small to warrant an avoidance of a utomated sample handling in routine screening or quality assurance pro grammes where the increased throughput allowed is advantageous. It was also noted that the use of citric acid to acidify the chromatographic solvents was not superior to acetic acid.