RESUMO
In this study, a simple and sensitive fluorimetric method was described for the determination of Ascorbic Acid (AA). The procedure is based on the reaction between AA and Methylene Blue (MB). The fluorescence intensity of MB was measured at excitation and emission of 664 and 682 nm, respectively. MB concentration was decreased as a function of decreasing fluorescence intensity due to forming colorless form of MB (Leuco-MB) in the reaction between AA and MB. A linear relationship was obtained between the decreasing fluorescence intensity and the concentration of AA in the range of 3.0 x 10(-7)-6.0 x 10(-6) mol.l(-1). The detection limit was 2.5 x 10(-7) mol.l(-1). The proposed method was applied successfully for the determination of AA in Vitamin C tablets.
Assuntos
Ácido Ascórbico/análise , Azul de Metileno/química , Ácido Ascórbico/química , Calibragem , Estrutura Molecular , Sensibilidade e Especificidade , Espectrometria de Fluorescência/métodos , Comprimidos/química , Fatores de TempoRESUMO
The electrochemical behavior of a copper(I)oxide (Cu(2)O) modified carbon paste electrode (MCPE) was investigated in different buffer solutions and in the presence of ascorbic acid (AA) and cysteine (RS). Working conditions such as pH, mineral oil, and modifier ratio were optimized. Voltammetric results revealed that RS forms rather stable complexes with Cu(I) which has a high electrocatalytic reduction peak current at -0.65V versus SCE in borate buffer (pH 9.2). In the case of AA, a complexation occurred with Cu(II) species at the electrode surface, rather than Cu(I). The electrocatalytic reduction peak current of the Cu(II)-AA complex was observed at -0.07V in phosphate buffer at pH 6.9. Linear responses were observed in the range 2.0x10(-9) to 3.0x10(-8)M with a 0.9954 correlation coefficient for RS and 1.0x10(-9) to 2.0x10(-8)M with a 0.9961 correlation coefficient for AA.
