i want to know the step by step process and how to eventually construct the graph and calculate the Quantity of the phytochemicals from the curve in mg/g
You can use reference in phytochemistry which is explain the fractionnation of plant extract, in this operation you may use solvents with the volume exactly and calculate the weight of each fraction/mass of plant extract. I think that is the first step is to precise each operation in drawing the plan of the fractions.
first you should isolate the compound that you want to check his amoutnt in the extract and then you prepare different concentration of that amount for ex ( 1 mg/ml , 0.5 mg/ml , 0.25 mg/ml ... ) then you inject your samples in HPLC and you detect the area under the curve of each concentration and then you draw a calibration curve . Then you preapre exract sample for ex ( 10 mg/ ml ), you inject in HPLC then you check the area under the curve of your compound and finally you use the equation to get the concentration of your compound in the sample