To perform any bio-assay with different organic fractions of a plant part, mostly methanol crude extract is partitioned with different solvents in increasing order of polarity using a separating funnel, is not it better to extract the tissue separately with all solvents? If you have availability of plant in excess, what protocol should be preferred?
For the solvent-solvent partition for natural extracts we normally use "Kupchan" method of partitioning. Begins with the extract dissolving MeOH:H2O (9:1) solvent system then add equal amount of hexane. After hexane partitioning increase the polarity of the original mixture in to MeOH:H2O (6:4) then extract with CHCl3. Then evaporate all included MeOH using Rotary evaporator and finally add the EtOAc in to the remaining water layer. This is a modified version of the kupchan method. you will have 4 fractions (hexane, CHCl3,EtOAc and water)
Modern trend is the extraction of plant material with different solvents and then bioassay or biological activities.
I would not recommend your suggestion fully - you may try initially with different solvents but the aim here is to get as many as possible in the first step and then go on eliminating one by one in the next couple of steps. This is necessary because some solvents are better than the others in releasing a large variety of bioactives from the plant matrix - but if you are sure about what class of seconday metabolite you are looking into - you may go for a more specific extraction
For every method there is always need of economic consideration. If we use every time solvent for extraction of plant material it cost more and need more in bulk. Instead of doing this if we partition the solvent, it decrease the overall cost, time as well as work with same efficiency.
Partitioning is very useful in removing non-polar constituents eg lipids. if you are looking for polar compounds, it is wise to do partitioning with hexane to remove some of the impurities.
As mentioned by Dipjyoti Chakraborty that some solvents are more capable of extraction from plants like methnol. If we use water so it will leave the hexane soluble fraction definitely and dissolving the other natural products which are soluble in other solvents to some extent not like methanol. But if you are intersted in specific class of compound then off course you can use the procedure which will be tedious job.
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