Solid-Phase Extraction Spectrophotometric Determination of Total Antioxidant Capacity in Antioxidant-poor Samples by Using the Ferric-Ferrozine Method.

Ferrozine (FZ) preferentially stabilizes Fe(II) over Fe(III) to raise the ferric reduction potential and oxidize antioxidants. The advantages of the ferric-ferrozine method over other iron-based total antioxidant capacity assays were: (i) higher molar absorptivity and enhanced sensitivity, (ii) lower interference from foreign ions, (iii) wide pH tolerance (iv) additivity of the absorbances for mixtures. Solid-phase extraction (SPE) could be combined with spectrophotometry, because the magenta-colored anionic Fe(II)-FZ complex was quantitatively sorbed on Sephadex QAE A-25 resin.

Folin-Ciocalteu spectrophotometric assay of ascorbic acid in pharmaceutical tablets and orange juice with pH adjustment and pre-extraction of lanthanum(III)–flavonoid complexes.

Background: This study proposes modifications to the conventional Folin-Ciocalteu (FC) spectrophotometric method for individually determining ascorbic acid (AA) in complex matrices in the presence of other phenolics and potential interferents. The conventional FC assay in the aqueous phase,which normally measures total water-soluble phenolics and other antioxidants, has recently been modified by incorporating isobutanol (iso-BuOH) in the solvent mixture for the simultaneous determination of lipophilic and hydrophilic antioxidants in foods.

Results: Interference effects of other flavonoids and phenolics to individual AA assays were overcome by preliminary extraction–removal as their La(III) chelates into ethyl acetate (EtAc).

Modified Folin-Ciocalteu antioxidant capacity assay for measuring lipophilic antioxidants.

The Folin-Ciocalteu (FC) method of performing a total phenolics assay, originally developed for protein determination, has recently evolved as a total antioxidant capacity assay but was found to be incapable of measuring lipophilic antioxidants due to the high affinity of the FC chromophore, that is, multivalent-charged phospho-tungsto-molybdate(V), toward water. Thus, the FC method was modified and standardized so as to enable simultaneous measurement of lipophilic and hydrophilic antioxidants in NaOH-added isobutanol-water medium. Optimal conditions were as follows: dilution ratio of aqueous FC reagent with iso-BuOH (1:2, v/v), final NaOH concentration of 3.

Comparative evaluation of Fe(III) reducing power-based antioxidant capacity assays in the presence of phenanthroline, batho-phenanthroline, tripyridyltriazine (FRAP), and ferricyanide reagents.

The chemical diversity of antioxidants in complex matrices such as plant extracts makes it difficult to separate and quantify antioxidants from these solutions. Therefore it is desirable to establish methods that can measure the total antioxidant capacity (TAC) levels directly from plant extracts. Iron(III)-based TAC assays, especially the most widely used FRAP (ferric-reducing antioxidant power), play an important role in this regard.