An aqueous extract is prepared and 1 gm of crude extract is dissolved in 100ml of distilled water. From this various ppm like 25, 100, 500, 1000, 2000
and 3000ppm are prepared. For ex. 100 ppm prepared by taking 0.5 ml of
stock solution + 49.5 ml of deionised water in a 100ml beaker. To this 10 larvae is added and observed for 24, 48 hrs. But there is no mortality observed. what mistake made in this methodology. Can anyone give me suggestions.
ppm is a weigth proportion and 1000 ppm equal 0.1% or 1g per Kg. Often the lack of activity depends on degradation of active principles during extraction by heat or oxidation. Active doses are evaluated by log scale like 1 10 100 1000 ppm. Thus you should take your start as 10000 ppm by weight, 10 g of it in 100g of solution would be 1000 ppm and so on. If inactive check extraction and reference, bye
you could dissolve 1 g in one liter of distilled of distilled water. this would give exactly 1000 ppm. from this you could easily prepare other concentrations, as this is a stock solution.
ppm from plant extract is quite differernt from ppm of active ingredients. Raw extraction may be helpfull to determine interesting fractions but concentration of active substance(s) may be of importance.
Asha! I completely agree with Patrice ... Crude extracts are involve huge quantity of different chemicals. I, my self work on nematicidal properties of plant extracts and I use 5000 ppm as the base concentration , it is really hard to observe mortality in lower concentrations. you should increase it and go head for your primary bio-assay.
To have some activity, you have to isolate polar, semi polar, and non-polar fractions from the crude extract, using polar, semi polar, and non-polar solvents; after that, you can test each extract individually. Dissolve one gm of the extract in the minimum amount of suitable solvent and complete to 1000 ml with water. For semi and non- polar fractions, you have to add a surfactant with the organic solvent before dilution with water. Test each extract at 1000 ppm first; the fraction that give you a strong activity at 1000 ppm should be tested at a series of lower concentrations.
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