ABSTRACT The prevention of chronic and degenerative diseases, is a health concern deeply associated with oxidative stress. Such progressive phenomena can be avoided through exogenous antioxidant intake, which set up a reductant cascade, mopping up damaging free radicals. Medicinal herbs are commonly associated with high antioxidant potential, and hence their health benefits. The commerce of dried herbal extracts movements a big portion of developing countries economy. The determination of medicinal herbs the antioxidant activity capacity is of utmost importance. The assessment of antioxidant activity in phytotherapics is mostly achieved by spectrophotometric assays, however colored substances can produce interferences that do not occur in electroanalytical methods. Therefore, the aim of this paper is to compare spectrophotometric and voltammetric techniques to evaluate antioxidant activity in herbal drugs such as: Ginkgo biloba L., Camellia sinensis (L.) Kuntze, Theaceae; Hypericum perforatum L., Hypericaceae; Aesculus hippocastanum L., Sapindaceae; Rosmarinus officinalis L., Lamiaceae; Morinda citrifolia L., Rubiaceae; Centella asiatica (L.) Urb., Apiaceae; Trifolium pratense L., Fabaceae; Crataegus oxyacantha L., Rosaceae; and Vaccinium macrocarpon Aiton, Ericaceae. The spectrophotometric methods employed were DPPH (2,2-diphenyl-1-picrylhydrazyl), ABTS (2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) and the Folin-Ciocalteu assays. The electroanalytical method used was voltammetry and it was developed a phenoloxidase based biosensor. The redox behavior observed for each herbal sample resulted in distinguishable voltammetric profiles. The highest electrochemical indexes were found to G. biloba and H. perforatum, corroborating to traditional spectrophotometric methods. Thus, the electroanalysis of herbal drugs, may be a promising tool for antioxidant potential assessment.

A simple and fast method for the determination of nimesulide (NI) using flow injection analysis with multiple-pulse amperometric (FIA-MPA) detection at a boron-doped diamond (BDD) electrode was developed. The method was based mainly on the application of a four-potential waveform, E1(det) = -0.8 V / 30 ms, E2(det) = 0.6 V / 30 ms, E3(det) = -0.4 V / 30 ms and E4(cleaning) = -0.45 V / 300 ms versus Ag/AgCl (3.0 mol L-1 KCl). NI was detected at three different electrode potentials, at which the nitro group undergoes different redox reactions. The proposed method was selective and sensitive (detection limit of 81.0 nmol L-1), and successfully applied for the determination of NI in pharmaceutical formulations, yielding similar results to those obtained by the reference method.

The potentialities and applications of the Multiple Pulse Amperometric detection (MPA) coupled with Flow Injection Analysis (FIA) are evaluated. Important aspects as cleaning and activation of electrode surface, indirect and simultaneous analysis of electroactive compounds and the use of the internal standard method for quantifications utilizing FIA-MPA are presented. The main parameters concerning the detection of electroactive analytes by multiple pulse amperometric detection in flowing solutions were also discussed. In addition, aspects such as flow rate, sample volume, application time of the potential pulses and instrumentation necessary for implementing of the method were also addressed.