de Mattos Ivanildo Luiz, Zagal José Heraclito
Departamento de Química de Los Materiales, Facultad de Química y Biología, Universidad de Santiago de Chile, Casilla 40, Sucursal Matucana, Santiago 9170022, Chile.
Int J Anal Chem. 2010;2010:143714. doi: 10.1155/2010/143714. Epub 2011 Mar 3.
A flow injection system using an unmodified gold screen-printed electrode was employed for total phenol determination in black and green teas. In order to avoid passivation of the electrode surface due to the redox reaction, preoxidation of the sample was realized by hexacyanoferrate(III) followed by addition of an EDTA solution. The complex formed in the presence of EDTA minimizes or avoids polymerization of the oxidized phenols. The previously filtered tea sample and hexacyanoferrate(III) reagent were introduced simultaneously into two-carrier streams producing two reproducible zones. At confluence point, the pre-oxidation of the phenolic compounds occurs while this zone flows through the coiled reactor and receives the EDTA solution before phenol detection. The consumption of ferricyanide was monitorized at 360 mV versus Ag/AgCl and reflected the total amount of phenolic compounds present in the sample. Results were reported as gallic acid equivalents (GAEs). The proposed system is robust, versatile, environmentally-friendly (since the reactive is used only in the presence of the sample), and allows the analysis of about 35-40 samples per hour with detection limit = 1 mg/L without the necessity for surface cleaning after each measurement. Precise results are in agreement with those obtained by the Folin-Ciocalteu method.
采用未修饰的金丝网印刷电极的流动注射系统用于测定红茶和绿茶中的总酚含量。为避免因氧化还原反应导致电极表面钝化，样品通过铁氰化钾（III）进行预氧化，随后加入乙二胺四乙酸（EDTA）溶液。在EDTA存在下形成的络合物可使氧化酚的聚合最小化或避免其聚合。将预先过滤的茶样品和铁氰化钾（III）试剂同时引入两个载流中，产生两个可重现的区域。在汇合点，酚类化合物在该区域流经盘管式反应器并在检测酚之前接收EDTA溶液时发生预氧化。以银/氯化银为参比电极，在360 mV处监测铁氰化物的消耗，其反映了样品中酚类化合物的总量。结果以没食子酸当量（GAEs）表示。所提出的系统稳健、通用、环保（因为仅在有样品时才使用试剂），并且每小时可分析约35 - 40个样品，检测限为1 mg/L，每次测量后无需进行表面清洁。精确结果与福林 - 西奥尔特法所得结果一致。
