Dear Rolayo,

This depends on the 'fluffiness' of the dried, powdered plant material. The best way is to use the volume of solvent that completely soaks the powdered plant material and add excess to completely immerse. Check the volume of the solvent used. After draining after first extraction, use the same volume for second and third extractions.

To determine the number of extractions required, check the dry material obtained in each extraction. Mostly 3-4 extractions should be sufficient..

For flavonoids: Extract in methanol or Methanol: water (70: 30 or 80: 20) and then defat the concentrated extract in n-hexane. discard the n-hexane extract and use the defatted residue for analysis/purification of flavonoids.

For alkaloids: Extract in methanol. concentrate to dryness. resuspend in dilute sulphuric acid (should be

I would suggest you to use a Soxhlet extractor. This will allow you to use the same solvent for extracting the crude drug again and again. Moreover you can also recover the solvent from the extract in the end and use it for further extraction for another batch of the same material. Regarding the methods for extracting flavonoids and alkaloids, you can follow the procedure suggested by Dr. Suresh or also you can consult some phytochemistry books like 'Medicinal Plant Alkaloids' by Stephen Sim, Trease and Evans 'Pharmacognosy', Harborne JB - 'Phytochemical Methods' etc. Normally it is better to defat the plant material prior to extraction using n-hexane or petroleum ether. Then you can proceed with different solvents in the order of increasing polarity from ethanol to water. Choice of solvent depends upon the solubility of the target compound in a particular solvent.

Gud Luck and Regards

Dear Dr.Rolayo,

Missed to mention! (after reading Dr.Alok's comments). If you are interested in generating small samples for sample analysis (by HPLC/HPTLC or other deconvoluting techniques), you should use Soxhlet as suggested by Dr.Alok. However, if you are interested in large samples (say from >10 kgs of dried plant material), I would suggest cold extractions (percolation or maceration) as I mentioned earlier. Larger sample sizes are ideal for purification of constituents. Harborne's book would give you more or less what I have outlined, if you are looking for alkaloids. Acidifying initial extract and partitioning with EtOAc would remove all the acidic and neutral material and once you basify and extract the alkaloid fraction, you have automatically eliminated the acid and fatty material. However, the EtOAc fraction from the acid extract can be dried and defatted using n-hexane, to provide flavonoid/phenylcarboxylic acid mixtures. Such pH based solvent partitioning is quick and avoids use of too many solvents in the process which makes it cost prohibitive, especially if you are planning to purify alkaloids / flavonoids from one starting herb material in a semi-prep or prep scale.

In a simple way , it is better to use the volume of solvent that completely soaks the powdered plant material and add excess to completely immerse. After first extraction, use the same solvent in less volume for second, third or sometimes fourth extraction.

The solvent volume has cover the whole plant material, and its wiser to reapeat the extraction 2 or 3 times, just to make sure you dissollve as mush isolate as possible. If you have less solvent shaking always helps.

Earlier studies reported that solvent to sample ratio of 10:1 (v/w) has been used as ideal (Pandey and Tripathi, 2014) [Pandey A, Tripathi S. Concept of standardization, extraction and pre phytochemical screening strategies for herbal drug. Journal of Pharmacognosy and Phytochemistry 2014; 2 (5): 115-119.] [https://pdfs.semanticscholar.org/66ca/51cff240ef5d4986e906db8ba39bf45c42e1.pdf].