Dear Colleague

I am testing antioxidant activity for some cinnamic acid derivative, and already finished with DPPH, ABTS and now still working with total antioxidant capacity (reagent solution; sulphuric acid (0.6 M), sodium phosphate (28 mM ) and ammonium molybdate (4 mM) which dissolved in distilled water. using different concentrations of Ascorbic acid in methanol. each sample was added 0.6 mL of ascorbic acid and 2.4 mL of reagent and incubated at 95°C for 90 min. After cooling to room temperature; absorbance was recorded at 695 nm against reagent blank.

Is this the right method for testing or you have advice for me? Because the absorbance should be increase with concentration but it was changeable 0.004A, 0.005A, 0.001A, 0.015A, 0.006A, 0.038!