Methanol usually enriches more hydrophilic molecules than hydrophobic molecules.
However, why we commonly used methanol during extraction?
Methanol, even though an organic liquid, is a polar solvent. Thus, it can readily dissolve polar organic substances which are widespread in nature, and beneficial to man and other living organisms. Hence, it is commonly used as a solvent for extraction of natural materials.
I agree with what Raphael John Ogbe mentions, due to its polarity, methanol can extract both polar and medium polar compounds, but it all depends mainly on the type of compounds you are interested in extracting because if you are looking to extract apolar compounds you will have to opt for another solvent such as hexane and chloroform. Besides that, it is necessary to consider the use you want to give the extract, since if you require it for use in some food product or some biological evaluation, always opt for less toxic solvents, such as ethanol and water.
Dear A S M Ali Reza that's a very good question which is clearly of broad general interest to many other RG members as well. Quite often the goal of extracting plant materials is the isolation of polar natural product such as polyphenols, flavonoids etc. These can subsequently be used e.g. for the "green synthesis" of various nanoparticles (gold, silver) because of their reducing / anti-oxidant properties. For the extraction of such polar natural products a highly polar solvent such as methanol is particularly suited. Methanol also has the advantage that is has a low loiling point so that the extracts can be easily concentrated.
Many useful references about the extraction of plant materials can be found in the literature. For typical examples, please have a look e.g. at the following relevant articles:
Effect of Extraction Solvent/Technique on the Antioxidant Activity of Selected Medicinal Plant Extracts
and
Solvent extraction effects on phytochemical constituents profiles, antioxidant and antimicrobial activities and functional group analysis of Ecballium elaterium seeds and peels fruits
(see attached pdf files)
Please note that these are just two of very many relevant research articles about this topic. For more information, please also search the "Publications" section of RG.
I hope this helps. Good luck with your research work and best wishes, Frank Edelmann
Dear Professor @ Edelmann, thank you for your information. It will really be helpful for natural product researchers.
But I am wondering another thing, that we observed that some researchers have been using hydroalcoholic solvents such as 70% or 80 % methanolic or ethanolic solutions. Are there any specific reasons or advantages for using this form?
Thanks again, professor.
Dear A S M Ali Reza thank you for your kind response and question. I think the choice of solvent for plant extractions depends to a large extent on what kind of natural products you are interested in. You could for example start with non-polar pentane or petroleum ether which will extract e.g. certain oils and other non-polar plant materials. Then you can continue with more and more polar solvents until you end up with water. For more information about your question why 70% methanol / water mixtures are often used, please have a look at the answers given to the following closely related RG question:
Why do we mostly use methanol and water in plant metabolite extraction?
https://www.researchgate.net/post/Why_do_we_mostly_use_methanol_and_water_in_plant_metabolite_extraction
(6 answers)
I also suggest that you search the "Publications" section of RG e.g. for the term "plant extraction with aqueous methanol". This will provide you with a good number of helpful refereces which have been posted by RG members, some of them even as public full texts:
https://www.researchgate.net/search.Search.html?type=publication&query=plant%20extraction%20with%20aqueous%20methanol
For example, please have a look at the following freely available RG links:
Screening of aqueous methanol plant extracts for their antibacterial activity
Chapter Screening of aqueous methanol plant extracts for their antib...
and
Antimicrobial activity of aqueous methanol extract of plants
Book Antimicrobial activity of aqueous methanol extract of plants
Please stay safe and healthy! With best wishes, Frank Edelmann
Methanol is the most effective solvent for the extraction, giving the highest extraction yields and highest content of phenolic, flavonoid, alkaloid, terpenoids. One of the reasons why methanol is more used than other solvants including ethanol, is its boiling point. So, with methanol extract we need lower T° to evaporate the solvent in rotaryvapor, then the extract is less damaged. beacause methanol has the higher vapor pressure due to its molecules smaller than those of ethanol, so its intermolecular forces are less than ethanol's. To conclude, Methanol is the best suitable solvent to extract plant material.
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