Fluorospectrophotometric Determination of Traces of Nitrite Ion By Its Fluorescence Quenching Effect on Thionine

In a dil.HCl medium,the fluorescence of thionine was quenched by NO-2 due to diazotization reaction.The magnitude of decrease in fluorescence intensity (ΔF) measured at (λex) 602 nm and (λem) 622 nm,was directly proportional to the concentration of NO-2 ion in the range of 0.04-0.40 mg·L-1.The proposed method was used in the determination of trace amounts of NO-2 in samples of pickles,giving values of recovery in the range from 96% to 104%.