The evaluation of reduction of Fe(III) in 3-hydroxy-4-nitroso-2,7-naphthalene disulphonic medium as an alternative ferric reducing activity power assay.

INTRODUCTION: The growing interest in determination of anti-oxidant capacity through non-labour, effective and less costly methods encouraged the development of the spectrophotometric procedure presented in this study. OBJECTIVE: To investigate the reduction reaction of Fe(III) in 3-hydroxy-4-nitroso-2,7-naphthalenedisulphonic anion (NRS) medium as an alternative ferric reducing activity power (FRAP) assay for determining the total reduction capacity (RC). MATERIALS AND METHODS: The absorbance values at 730 nm were used to determine the RC of aqueous extracts of nine Brazilian plants. The results were compared with the values obtained with the 2,2-diphenyl-1-picrylhydrazyl (DPPH) method and with the total polyphenol content (TPC). The RCs of phenolic derivatives, flavonoids, amino acids and other anti-oxidant compounds were determined. RESULTS: Paired t-test with RC values obtained with both assays (proposed FRAP and DPPH) showed no statistically significant difference. In addition, the RC values from the proposed FRAP assay are proportional to those found with TPC values (r =0.916). In addition, the conditional reduction potential of the Fe(III)/Fe(II) couple (0.685 V vs NHE (normal hydrogen electrode)) and the molar absorptivities at 730 nm of the Fe(NRS)(3)(3-) and Fe(NRS)(3)(4-) complexes (1.88 × 10(3) and 1.77 × 10(4) L/cm × mol, respectively) were calculated because these values were not available. CONCLUSION: The proposed assay is adequate for determination of the RC of plant extracts, and the results infer that other samples derived from plants (e.g. beers and wines) and even biological samples (e.g. serum and urine) also could be analysed.

A critical study of use of the Fe(II)/3-hydroxy-4-nitroso-2,7-naphthalenedisulfonic acid complexes in the quantification of polyphenols in medicinal plants.

A critical study of the use of the Fe(III)/3-hydroxy-4-nitroso-2,7-naphthalenedisulfonic acid (NRS) complexes on the quantification of the polyphenols content in aqueous extracts of plants, expressed as pyrogallic acid, [PA], is presented. The reaction used is based on the reduction of Fe(III) to Fe(II) by [PA] in the presence of NRS in a buffered medium (Tris; pH 8.0) with formation of Fe(II)/NRS complexes. A calibration curve of absorbance (at 730 nm) vs. [PA] is linear (r=0.998; n=7) from 1.0 to 7.0 µmolL(-1) [PA]. LD and RSD were 0.5 µmolL(-1) and 2.5% (6.0 µmolL(-1) [PA], n=10), respectively. The influence of pH, type of buffer solution and interfering species possibly present in the samples were evaluated. Aqueous extracts of twelve medicinal plants used in the Brazilian folk medicine were analysed by using both Fe(III)/NRS complexes and the Folin-Ciocalteu reagent.