Desenvolvimento de um procedimento para fracionamento de manganês de chá preto e detecção por voltametria de redissolução catódica

Abstract

The medicinal properties of tea have been studied over the years. These properties can be attributed mainly to the presence of antioxidant species, such as flavonoids. Tea is a drink prepared by the infusion of leaves, bark, roots and leaves of some kind of plants, highlighting infusions prepared by Camellia sinensis. In addition to having biologically active compounds, tea could contain some metals considered essential for human development, among them is manganese. In some cases, these metals may be complexed in the presence of organic compounds, originally present in the infusion, contributing to its bioavailability increase. This dissertation presents the development of a procedure for the manganese fractionation black tea infusions using cathodic stripping voltammetry. The determination of the fraction relative to manganese bounded to organic matter was performed directly on the diluted sample, without an additional sample preparation step. For total manganese determination, an acid digestion step was implemented employing HNO3 and H2O2 (4:1). Electrochemical measurements were performed using a glassy carbon electrode as a working electrode, in acetate buffer medium (pH = 4.5). Linear responses were observed in the concentration range of 10 to 250 :g L-1. Relative standard deviation, limit of detection and quantification were estimated as 9.7% (n = 10), 0.06 and 0.2 :g L-1, respectively. The results obtained for the determination of free and total manganese in black tea samples were in agreement with the reference procedures