A clear methanolic extract solution obtained after filtration when concentrated gives a semi solid extract. Now this extract for a quantitative analysis needs to be taken by weight and made a solution in methanol but the solution is not a homogeneous one. Why at the start all the plant compounds dissolved in methanol and later on they do not dissolve?
In the original extraction, a larger volume of solvent (methanol) was used so it extracted a lot of components out before solvent evaporation (to give semisolid "crude" extract). When try to reconstitute this semisolid in a smaller volume of the same solvent, obviously there was not enough solvent to dissolve all of it. Similarly, when you do the Soxhlet extraction (say... 10 cycles - you recycle the solvents so it mimics the 10X extraction with fresh solvent volume, when actually you only have 1X volume), you will start seeing some precipitation when the whole extract cools down.
This question addresses two related principles: extractability and solubility. With methanol, you can extract a hexane soluble or water soluble compounds but once they are purified, they may not dissolve in methanol. The two process have a lot in common but also are different. When you extract compoundss in crude mixtures, they drag each other as well to to come out in high yield. So, what you observed was normal and expected.
In the original extraction, a larger volume of solvent (methanol) was used so it extracted a lot of components out before solvent evaporation (to give semisolid "crude" extract). When try to reconstitute this semisolid in a smaller volume of the same solvent, obviously there was not enough solvent to dissolve all of it. Similarly, when you do the Soxhlet extraction (say... 10 cycles - you recycle the solvents so it mimics the 10X extraction with fresh solvent volume, when actually you only have 1X volume), you will start seeing some precipitation when the whole extract cools down.
In the original extraction, a larger volume of solvent (methanol) was used so it extracted a lot of components out before solvent evaporation (to give semisolid "crude" extract). When try to reconstitute this semisolid in a smaller volume of the same solvent, obviously there was not enough solvent to dissolve all of it. Similarly, when you do the Soxhlet extraction (say... 10 cycles - you recycle the solvents so it mimics the 10X extraction with fresh solvent volume, when actually you only have 1X volume), you will start seeing some precipitation when the whole extract cools down.
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