Normally if you count the cycles, then 72 cycles is considered as good criteria for extraction of the soluble constituents. Another simple method to know whether the extraction is complete or not is using a watch glass and collecting the solvent dropping from the extractor. Carefully you can collect few mL of the solvent coming out after extraction. Don't allow it to fall in the round bottom flask. Collect it in a clean watch glass. Allow it to evaporate at room temperature. In another watch glass, take pure solvent being used for extraction. Compare both the watch glasses after drying. If you see a deposit in the former as compared to the latter, your extraction is not yet complete. If both of them are the same, it is an indication that no more extractive will be obtained with the same solvent. It is a sort of indigenous method, might appear a bit hazy but it works and works well. I use it very frequently and results are always accurate.

Regards

As you noted, there are a range of times that people use. People sometimes determine the time by the number of cycles (fill/siphon) based on the number of cycles per hour. Running 24 hours with 4-6 cycles per hour should get it done for you for most compounds assuming the desired compounds are reasonable soluble in your extraction solvent.

It also depends upon your size of plant materials. Powdered form means small size large surface area higher extraction yield which can reduce number of cycles of extraction as well as time and solvent consumption.

For defatted plant material 6-8 hrs are sufficient but needs more time if the plant material is extracted directly

Actually it depends on

1) the solvent you use

2) the solubility of you metabolite in the solvent itself.

3) if the metabolite is internal (hydrophilic solvent as MeOH) or external the cells (any solvent)

4) the size of the material to be extracted

Only if you know all these factors you can decide how many cycles to do

As far as I am aware if everything is OK 3 to 6 cycles should be enough.

Until the solvent coming down become colorless, more you run the assembly faster is the rate of extraction

Note: Place a dark color paper behind the assembly so as to see the color of solvent coming down from siphon tube

Gud luck

It depends on the type of constituent you want to extract, like flavonoids & glycosides can be extracted in 4-6 hrs.

there are number of things where we can interpret the complete extraction of secondary metabolites via soxhlet extraction, the best way to visually interpret is to see the color of cotton below the plant material in extractor if it has regained its original white color that means extraction is complete.

Technically, the decision to stop the soxhlet extraction of plant raw material depends upon many factors like purpose of extraction (qualitative or quantitative), thermostability of the desired phytochemical constituent, economic feasibility, nature of raw material and extracting media (solvent) etc. But if you do not want to go into such details then it can be done either by visual examination of color of the circulating liquid extract in the neck of the soxhlet after condensation (more common with extraction of colored metabolites) or by putting a drop of the circulating liquid extract on a glass plate and allow it to dry, if after drying, there is any residue left then one more cycle should be allowed and so on otherwise extraction process should be stopped.

Normally if you count the cycles, then 72 cycles is considered as good criteria for extraction of the soluble constituents. Another simple method to know whether the extraction is complete or not is using a watch glass and collecting the solvent dropping from the extractor. Carefully you can collect few mL of the solvent coming out after extraction. Don't allow it to fall in the round bottom flask. Collect it in a clean watch glass. Allow it to evaporate at room temperature. In another watch glass, take pure solvent being used for extraction. Compare both the watch glasses after drying. If you see a deposit in the former as compared to the latter, your extraction is not yet complete. If both of them are the same, it is an indication that no more extractive will be obtained with the same solvent. It is a sort of indigenous method, might appear a bit hazy but it works and works well. I use it very frequently and results are always accurate.

Regards

Yes..its the way to confirm the full extraction. Even then the target metabolites and its thermostability plays major role in soxhlation. As usual routine procedure cannot be followed in every case. For an unknown plant the general procedure can be followed.

Soxhlet extraction time depends on type, physical status and size of plant materials; extractant used and may vary with respect to its aspects. In general, for coarsely powdered materials, 70-80 drain off cycles are suggested. However, it is not possible to count every cycle; hence for a given extraction condition (i.e. Size of material, capacity of Soxhlet, temperature, etc) you can determine time of one drain off and accordingly estimate the total duration for 70-80 cycles. You should continue the extraction till the solvent is seen completely colourless then go more 2-3 additional drain-off to ensure complete extraction. You may also confirm the same as suggested by Alok.

The extraction process may continue for 24 hours or till the solvent in

siphon tube of an extractor become colorless.

This is really good question. From my point of view you have to run soxhlet till the solvent present in the soxhlet not show any of the spot in TLC plate. Means the solvent is not able to solubilise any other things present in the material. So as you get colorless solvent in siphon, you have to analyse that solvent in TLC plate. If either in UV or by dervitisation you could not get any spot with refrence to same blank solvent. Then only extraction is completed.

I just watch the solvent in the siphon when it become colorless then I leave the soxhlet running for few hours before stopping it.

I just wait and watch  for the solvent in the Soxhlet siphon to become colorless, then I leave the soxhlet running for few more cycles to confirm complete extraction, before stopping it.

So, for cross checking as I get colorless solvent in the Soxhleet siphon, I analyse that on TLC plate. If I could not get any spot with reference to blank solvent. Then only I Confirm the completion of extraction.

Note:  Run Soxhlet Apparatus till the solvent present in the Soxhlet did not show any of the spot on TLC plate. This means that, the solvent is not more able to solubilise any thing of the plant material.