Please refer these

https://www.academia.edu/8542434/qualitative_assessment_of_essential_oil_of_mint_and_palmarosa

http://www.pharmainfo.net/reviews/methods-estimation-multi-component-formulations-review

http://www.ncbi.nlm.nih.gov/pubmed/22213698

http://en.cnki.com.cn/Article_en/CJFDTOTAL-YYPF201307019.htm

Thanks for your reply Sir.

Would like to know about maintenace of stability of volatile components in herbal preparations as well.

Regards!

Dear Harleen

Store in cool temperature may be one of the option for maintaining stability of volatile components. You may also you salt form of some volatile base for enhancing stability.  

I hope the attached review on stability of essential oils may be of help to you.

Menthol is available in liquid, powder and crystallized forms in India. Powder and crystallized forms of menthol are fairly stable. It is common knowledge that menthol crystals are used by Indian Paan shop vendors for flavoring the paans. Menthol is also widely used in food (chocolates, chewing gums, paan masalas, herbal teas etc), cosmetic (powders, hair oils, mouth washes, tooth pastes, shaving creams etc.) and pharmaceutical (cough syrups, lozenges, pain balms etc.) products. Alternatively, you can also explore the use of Mentha arvensis dried leaves or leaf powder for formulations.

First of all you isolate the pure fraction from plant extracts using following techniques. First run TLC to know the type of fractions. After that Column Chromatography with HPLC, after isolated pure fraction run FT-IR, LC-MS, HNMR, CNMR for structure elucidation.  You can conduct qualitative laboratory test methods also. You can read my papers too.