if the solution contains only the plant extract, you can dry it and weigh, otherwise you'll need the standard

You can determine the concentration of a particular component of your extract with the Lambert-Beer law.

You can do that only if:

1) you can measure your sample spectrophotometrically at the proper wavelength for this component and

2) you already know the extinction coefficient (ε) at this wavelength which is necessary for the Lambert-Beer law

Dear George

As per my knowladge, Spectrophotometric method is only useful if solution contains known phytochemical as you suggested but in this case  the solution contains plant extract that means lot of different chemicals  present in solution. In such case I am agree to Lalrinzuali. In this way we can measure "Total Dissolved Solids" .

thank you all, dear Lalrinzuali i'm looking for a method except the one that you said.is there any apparatus that can use for this determination?

Dear Golnaz

Take a empty beaker. Weight it and pour some know quantity of solution. Evaporate on steam bath or electric heater. Keep in to dryer at 80 to 100 degree centigrade for half an hour so that any moisture remain will remove out. Put beaker in dessicator  to cool and weight again. Difference in weight is equivalant to dissolved solids in solution. This is general protocol of analysis

Good Luck

Dr Ajay

dear Golnaz,

 i agree with Dr. Rajani...... if you want to know the concentration of a particular compound, you can use HPLC but i cant think of any instrument that can measure the concentration of plant extract since plant extract contains several compounds