Analysis of polyphenols and methylxantines in tea samples by means of nano-liquid chromatography utilizing capillary columns packed with core–shell particles

In this study, a rapid separation of eleven polyphenols and three methylxanthines was obtained by means of nano-liquid chromatography (nano-LC), employing a 100 μm I.D. capillary column packed with C18 core–shell particles (2.7 μm) for 10 cm. All compounds were baseline resolved with a step gradient elution in less than 15 min. The developed analytical method was validated and the resulting RSD% for intra-day and inter-day repeatability, related to retention time, retention factor and peak area, were below 5.1 and 5.7%. LOD and LOQ values corresponded to 0.300 and 0.625 μg/mL, while linearity range assessed gave R2 no lower than 0.990. Then, the method was used to determine studied compounds in tea extracts. Further, the nano-LC system was coupled with a mass spectrometer to confirm the components present in real samples. Finally the results were compared with those obtained using a capillary column (100 μm I.D. × 10 cm) packed with C18 sub-2 μm particles, applying the same nano-LC experimental conditions.