Several teqnics could be used for volatile fraction within extract or with freashly collected sample both we applied GC MS. There are biological and phytocemicals diversity within your sample due to time of collection and environment diversity. Biological tests will be done according to phytocemicals profile of your sample or according to letratures by application of new test not detected in your literature overview.

You must consider some factors, such as, your 'finance' strength, availability of a supervisor and then must have read several articles in the literature probably after contacting a pharmacologist or medicinal chemist to have a research discussion. Otherwise, many people would only suggest what they feel without knowing your capability. Again, as a physiology grad student, I suggest you look for a research area where you may build on finding mechanism of action of a plant metabolite to treat a dreadful or an important disease in your neighbourhood. Remember, you will be questioned on what prompted you to carryout the study as your justification of the study, during viva voce, so it is not what people feel...they can only advice if all above are set and catered for.