I will give an indirect answer to your question. If you have pure sample of catechins (I think they can be purchased from the market), co-inject a sample along with your tea sample and look for peak enrichment. You can repeat the experiment a couple of times for confirmation and your satisfaction.

Alternatively, you can contact Tocklai Tea Research Institute of Tea Research Association (http://www.tocklai.net/) for help and guidance.

Thank You Very Much, Sir.