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 3.0107—6.0106 mol· l1. The detection limit was
2.5107 mol· l1. The proposed method was applied successfully for the determination of AA in Vitamin C
tablets