Fluorometric determination of ascorbic acid in the abscence of the oxidant in juices of common citrus

A simple and sensitive fluorimetric method for the determination of ascorbic acid (AA) in juices of common citrus is described. The method is based on the condensation reaction between AA and o-phenylenediamine (OPDA) in the absence of the oxidant [1]. The fluorescence intensity is measured at excitation and emission wavelengths of 330nm and 430nm, respectively. Under optimum conditions, a linear relationship is obtained between the fluorescence intensity and the concentration of AA in the range 0.05–50µg mL^–1. The content of AA (mg/100 mL) in fresh juice of white grape was 30.5, red grape 28.0, orange 15.8 and lemon 16.8mg. The results obtained with our method are comparable with other methods [2]. The detection limit (3σ) was found to be 0.54µg mL^–1 of AA (σ from 5 determination of 10µg mL^–1). A relative standard deviation of 1.4% was recorded for 8 measurements of 1µg mL^–1 standard AA solution. The recovery for 50µg mL^–1 of AA added to samples of fresh citrus juices was between 101.5 and 104.6%. The effect of the reaction time is also studied. The fluorescence intensity of the system reached a maximum immediately after all the reagents were added and remained stable at least for 45 minutes. Presented method is simple, sensitive and easy for the determination of AA in the biological samples. This is first report that analyses of AA in biological samples were done without oxidant.

References: 1. X, W. et al. (2003) Talanta 59, 95–99.

2. Eitenmiller R.R., Ye, L., Landen, W.O. Jr.(2008) Vitamin analysis for the health and food sciences, CRC Press.