Phenolic profiling of complex tea samples via simultaneous multiplexed detection employing reaction flow HPLC columns and colorimetric post column derivatisation

A novel approach for the analysis of phenolics in tea was developed using multiplexed simultaneous detection. This is the first study employing a short reaction flow (RF) chromatography column (length 50 mm) for the analysis of phenolics in complex samples (not a standard mixture of compounds). RF separation efficiency was high as the detectors are multiplexed simultaneously, rather than sequentially. The delay time between RF detection responses is minor (1.2 s) providing simple peak assignment between the phenolic detection and conventional detectors, such as the UV and fluorescence detectors (FLD). Thirty-nine phenolics were detected amongst the five different tea samples (three from Camellia sinensis and two herbal teas). The highest number of phenols detected was 24 for English Breakfast tea (four highly abundant), 19 for Earl Grey (six highly abundant), 13 in Pure Green (two highly abundant) and 9 in both Fruit of the Forest (two highly abundant) and Camomile (none highly abundant) herbal teas. Numerous low concentration phenolic compounds in the Fruit of the Forest tea were not included due to their abundance being only slightly above the noise level of the detection process. The relative response factor (RRF) analysed at 520 and 500 nm aided to identify unique phenolics to each sample with similar retention times; three phenolics were unique to the Pure Green tea (2.30, 4.11 and 5.80 min) and two to the Earl Grey Tea (4.11 and 5.80 min). The Fruit of the Forest tea and the Camomile tea were both distinctly different from all other teas. This approach may be used for phenolic profiling of food, beverages or natural products.