Our friends at Chromatography Today published an 
interesting finding recently about how HPLC has been used to examine the chemical differences between fresh-brewed tea and bottled tea.
Here’s an excerpt:
Dr Shiming Li, a natural product chemist at New Jersey biotechnology firm WellGen, led a team using HPLC to analyse polyphenol levels in fresh tea and in bottled health drinks.
In some cases, the bottled beverages had levels of the antioxidants equivalent to around five per cent of the quantity seen in a single freshly brewed cup of either green or black tea.