Analytical Sciences

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

Kadriye Isil BERKER,* Dilek OZYURT,* Birsen DEMIRATA,* and Resat APAK**,***

*Department of Chemistry, Faculty of Science and Letters, Istanbul Technical University, 34469 Maslak, Istanbul, Turkey
**Department of Chemistry, Faculty of Engineering, Istanbul University, 34320 Avcilar, Istanbul, Turkey
***Turkish Academy of Sciences (TUBA), Piyade Street No: 27, 06690 Cankaya, Ankara, Turkey

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. The sensitivity enhancement using the resin enabled us to conduct total antioxidant capacity (TAC) measurements of antioxidant-poor samples. The apparent molar absorptivity, linear concentration range and trolox equivalent antioxidant capacities (TEAC) of certain antioxidants were found. The calibration curves (lines) of trolox, rutin, and rosmarinic acid individually and in herbal infusions—by using the method of standard additions—were parallel, confirming that the added antioxidants did not interact with herbal constituents to cause chemical deviations from Beer’s law.

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