Autographic assay for the rapid detection of antioxidant capacity of liquid and semi-solid pharmaceutical formulations using ABTS•+ immobilized by gel entrapment.

An autographic assay suitable for the detection of antioxidant compounds in a complex matrix (liquid and semi-solid pharmaceutical formulations) or in isolated compounds was described. The pre-formed radical monocation of 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS(•+)) was generated by oxidation of ABTS with potassium persulfate and reduced in the presence of hydrogen-donating antioxidants. For a further comparative estimation of its applicability and sensitivity, different medicinal plant extracts, hydrogels and antioxidant compounds were dot seeded or chromatographed on silica gel (TLC) and revealed with ABTS(•+) solution (System I) or ABTS(•+) immobilized by gel entrapment (System II). Both systems were effective and able to detect antioxidant activity in a micromolar range in seconds. System II was more sensitive and reproducible than System I. This micromethod is quick, inexpensive, and particularly helpful whether it works with numerous samples or on a small scale.