I did assay by following procedure:
A 40 mM solution of H2O2 was prepared in 50 mM of a phosphate buffer at pH 7.4. The concentration of H2O2 was determined by absorption at 230 nm using a spectrophotometer (UVmini-1240, Shimadzu Co., Kyoto, Japan).
20–60 μg/mL of seaweed extract was added to H2O2, and absorbance at 230 nm was determined after 10 min against a blank solution of methanol containing a phosphate buffer without H2O2. 0.1 M of ascorbic acid was used as standard. The percentage of H2O2 scavenging was calculated as
% Scavenged (H2O2) = [(Ai − At)/Ai] × 100 (1)
where Ai is the absorbance of the control, and At is the absorbance of the test or standard. The IC50 value (mg/mL) is the concentration of the sample or standard required to scavenge 50% of H2O2 free radicals.
But after calculation I got percentage of inhibition as negative values
https://www.alliedacademies.org/articles/in-vitro-antioxidant-activity-and-free-radical-scavenging-potential-of-roots-of-malawian-trichodesma-zeylanicumm-burm-f.pdf
Dear Kevin Salamanez,
the absorption wavelength is normally 230nm, not 560nm.
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