[Determination of ascorbic acid by indirect fluorimetry]

Experiments indicated that cerium(IV) ion which could not emit fluorescence was deoxidized by ascorbic acid to cerium(III) ion which could emit its characteristic fluorescence in water solution, while sodium hexametaphosphate added could greatly enhance the fluorescence intensity of the system. From this, an indirect sensitive method for determining ascorbic acid was developed. The fluorescence intensity of the system was measured in a 1 cm quartz cell with the excitation and emission wavelengths of 303 and 340 nm, respectively. The results showed that the fluorescence intensity of the system presented a linear relationship with the concentration of ascorbic acid in the range of 1.0 x 10(-7)-8.0 x 10(-6) mol x L(-1), the correlation coefficient r was 0.9997, and the detection limit (S/N = 3) was 1.6 x 10(-8) mol x L(-1). The presented method was used to determine ascorbic acid sample and vitamin C tablet, and the results were satisfactory.