Fluorescence Characteristics of Benzidine and Its Application to Determination of Microgram Quantities of Nitrite

Abstract

1. Fluorescence characteristics of benzidine was examined. Benzidine had an emission maximum at 387 nm under excitation at 295 nm in 90% ethanol. The fluorescence intensity increased the most in 70% ethanol. The concentration of HCl in 70% ethanol also influenced the fluorescence intensity. 2. The nature of fluorescence of benzidine was changed by the treatment with nitrite. The wavelengths for both excitation and emission maxima shifted to 275 and 348 nm, respectively, and its fluorescence intensity decreased to about one-third that of benzidine. 3. For the determination of nitrite, a fluorescence measurement was carried out at 326 and 387 nm for excitation and emission, respectively. The best results was obtained from the following procedure. Benzidine is treated with nitrite at 98°for 1 min in 0.1 NHCl and the mixture is diluted 10-fold with ethanol, then the fluorescence intensity is measured. Under these conditions, 0.25 to 1.25×10^-6M nitrite was successfully determined by the use of 10^-6M benzidine. 4. Among cations tested, Cu²⁺, Sn²⁺, Fe²⁺, and Al³⁺ interfered seriously with the determination of nitrite at a concentration of 5×10^-4M. Among the anions, citrate, malonate, thiocyanate, molybdate, and tungstate also interfered at a level of 10^-4M. Oxidants and reductants had also a serious effect on the determination of nitrite at a level of 5×10^-5M.