Aqueous extracts mostly contains more polar secondary metabolites like carbohydrates, sugars and glycosides which may not have sufficient antimicrobial action. Very rarely it contains hydrolysable tannins -  specific antimicrobial agents, where it cant be avoided. It is basically depend on the nature of plant and the secondary metabolite focussed.

No i do not think or believe there is any flaw with your design with mixed solvent. The choice of solvent is entirely your but you have to be sure you now what you want. The solvent you choose will determine what secondary metabolites you get from your plant. If the solvent mixture is what will give you the optimum polarity to get your desired anti cancer metabolite out, then by all means go ahead with that mixture.

no you cannot , because you can't justify which of the fraction is active.so youcan better go for testing with pure solvent.

Hi Anu,

I have been involved into thousands of extractions for discovery projects. There are no rules how to proceed. There are a few studies published on this subject. Prominently, from the scientists at NCI.  Generally, it is best to achieve as complete extraction as possible. Mixed solvents are usually more effective (why not to use them?). Traditionally, European tinctures are done with 70% ethanol, for example. Methanol is fairly universal solvent, but there are no truly universal solvents. You always make a compromise. But instead of using multiple extraction it is better to get one extract and afterwards partition it between different phases.

With my experience, I can say that It is better to consider this situation:

Plant extract should always be prepared in different/desired solvent(s)-extraction medium- separately for getting the targetted compound classes.

For good extraction use different dilution 10%, 20% 50% 70% 90% 100% in case of water soluble solvents separately, then freeze dry the extract to get concentrated extract/powder form

@Anu

Why not you do do study this

1. Plant extracts prepared using  individual solvents and 

2. Plant extracts prepared using mixture of solvents

And then do LCMSMS or NMR spectral analysis to see what you get in each situation and what you loose-qualitatively and quantitatively- when mixture is used

Explore nanoparticles encapsulation in case of non-water soluble residues for targeted delivary of the compound at the site

Please Know details about successive solvent extraction, one should know this, or the general order for extracting plant active ingredients/Isolating bioactive i.e. 

Pet. ether < Chloroform < Ethyl acetate < Alcohol (ethanol/methanol)

Pet. ether isolates all fatty material from plant

Chloroform isolates alkaloids generally

Ethyl acetate and alcohol isolates flavonoids and other similar compounds.

Like wise entire plant active constituents are isolated.

Phytochemical screening is carried for all this extracts

Biological activity is screened and possibility of active ingredients likewise responsible is known

No problem! you can  use hydro-ethanolic extract for biological activity testing. it is better then pure solvent extraction because hydro-ethanolic extract contains non-polar as well as polar compounds too. What I suggest you that it is better to use 90-95% Ethanol (but not 100%) for extraction and then go for fractionation with pure solvents of different polarity i.e. one non-polar, one moderately polar and one highly polar solvent.

If you use a pure solvent, it will avoid the impurities from the solvent that may have some negative/positive effects on your tests.

I Anu, I agree with the fact there is no rules for that. If you know the active compound to extract you have to proceed with the best solvent (polar or not polar). But sometimes, the compound is linked very stongly and you need to proceed with different step, sometimes using gradient (and thus mixture of solvent) but generally in the last step a pure extraction is better if you want to test the compound in vivo. Effectively some solvents are toxic ou can act on the compound in vivo and you could need to evaporate or lyophylisate before redilute in an appropriate one (when possible because some molecule after drying or lyophylisation becames insoluble definitely!). Sometimes, if the compound have acidic residue you could need to produce ester in order to dilute after in a water based more easy to manipulate. Sometimes some active principle are totally insoluble excepted in very agressive, toxic or physiologically active solvent (i;e; DMSO). In this case, tempting to overdilute in Water or alcool can be a way to reduce toxic solvent effect.but it is not a clean approach just an obligation. Excepted with water, never forget that even in alcool you could have side effects...and If methanol is often used, do not forget that this alcool is very toxic for human on long terms even if only inhaled. I know that rats are more resistant and generally only serve for one trial but more and more protocols of developments of new drugs needs cleaner approach as possible! Good work and luck!

Of course, you can use hydro alcoholic extract for your study. Solvent does't matter. it is only phytoconstituents present in the extract, which is responsible for activity.  

There is no rule that for extraction we should use pure solvents with reference to ethanol.Hydro Alcoholic solutions of various combinations can be used.The idea is that the solvent should be able to extract  the maximum number of  compounds present in the plant so that we  do not miss the activity because of Ineffective Extraction.For this purpose you can extract the Plant  with Alcohol:Water  in the ratio of  70;30,50;50,30;70

and Pure Alcohol and Pure Water.Test all the extracts.

Hello Anu..

There is no such rule that you have to use  pure solvents for plant extracts. You can use pure solvents as well as you can go for mixture of solvents too.

But for animal experiments you have to check the toxicity level for the pure solvents or mixture of solvents in cells line as well as in the murine model.

In another point how you will make sure that how much percentage of your solvents will be present in your plant extract that percentage should go for the vehicle treatment group.

Along with other vehicle you have to add this solvents as a separate or combine vehicle group.

Wish you best luck....

For invivo activity if you know or predicted the responsible constituent then it will be better to go for pure single solvent extraction selected on the basis of solubility of required constituent.If the constituent responsible for activity is not known or can not be predicted then generally mixed solvent (Alcohol: Water) is used so that constituent soluble in alcohol as well as water will be extracted. It cover polarity range form 5.2 to 9 and extract maximum constituents. It is more preferred because this extracts almost all constituents except fatty/ oily constituents.