I performed ABTS assay for my plant sample and standard ascorbic acid. The absorbance recorded was very low and in some case, even negative values were obtained. The procedure includes:

ABTS 7mM and ammonium persulphate 2.45 mM (mixed in equal volume) for generation of ABTS cations (kept in dark for 12-16 hours).

I used potassium persulphate also in place of ammonium persulphate, but similar results were obtained.

The absorbance of ABTS cations was adjusted to 0.700 @ 734 nm by using ethanol.

For different conc. of plant extracts (20-100 ug/ml) 1ml of ABTS was added, kept in dark and absorbance was recorded @ 734 nm after 30 min.

But the absorbance was not found in decreasing order. Control absorbance is also very low. The solution becomes colorless even for the lowest conc. of plant extract.

Kindly provide your valuable suggestions.

With Regards

PREETY