Chromogens ABTS

Another significant aspect was the stability of the radical chromogen ABTS in different solvents, in isocratic or gradient elution programs. We found that in the mobile phases used in our determinations (saline solutions and mixtures of organic solvents in different proportions), the observed fall was less than 0.01 expressed as — AAbs730nm/min. This stability is high... 

Fig. 5. A popular chromogenic substrate for assays of TAC, 2,2/-azinobis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS).

Several reductive assays have been proposed (Table 3). A test using reduction of l,l-diphenyl-2-picrazyl (DPPH) radical was introduced in the 1950s (B15) and has been used by various authors. DPPH is a stable free radical, which can be bought in substantia. It has an absorbance maximum at 515 nm (millimolar absorption coefficient e = 12.5 mM-1 cur1) (A15). A disadvantage of this chromogen lies in the fact that it can be dissolved only in organic (especially alcoholic) but not in aqueous media, which limits its use for studies of hydrophilic antioxidants. Reduction of ABTS also can be followed by electron spin resonance (ESR) (Yl). 

The adaptation of the ABTS" method as an on-hne test required that the chromogen radical should be stable for sufficient time in different solvents to permit the utilization of isocratic or gradient elution programs. The on-line reaction time between ABTS" and potential antioxidants was an additional potential limiting factor. 

Fig. 2 Instrumental scheme for the determination of antioxidant activities by HPLC using ABTS as chromogenic radical.

Determinations of antioxidant activity are widely used in phytochemistry, nutrition, food chemistry, clinical chemistry, as well as in human, animal, and plant physiology, etc. Methods adapted to HPLC have appeared only recently but can be expected to have multiple applications in the future. ABTS" is an excellent metastable chromogen for the detection and quantification of the HAA and LAA of biological samples. Thus, using a simple photometer (end-point method), a microplate reader (multisample titration method),or HPLC equipment, a broad range of possibihties are available for the characterization of diverse samples (animal- or plant-derived). Some applications of special interest could include ... 

TEAC assay uses ABTS chromogen radical absorption decay at 734 nm, H O and metmyc lobin as inducer, and Trolox as reference. 

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