Fluorescein mercury(II) acetate and sodium fluorescein as reagents for the determination of bis(2-chloroethyl)sulfide by fluorescence quenching Original Research Article

Bis(2-chloroethyl)sulfide causes strong quenching of sodium fluorescein and fluorescein mercury(II) acetate fluorescence in alcoholic media. Sodium fluorescein shows the greater promise as a reagent for its determination by fluorescence spectrometry with excitation at 366 nm and measurement at 518 nm. The results indicate a working range between about 3×10−7 and 4.5×10−5 mol l−1 bis(2-chloroethyl)sulfide in propan-l-ol. Reproducibility of the quenching effect was around ±10% relative standard deviation, for concentrations in the middle of the working range. Fluorescein mercury(II) acetate is similarly sensitive, but is unstable and suffers from photo-bleaching making it unsuitable for long-term application. The mechanism of the quenching is obscure but may involve protonation of the fluorescein, anhydrous hydrogen chloride having a similar quenching effect or, from earlier work by Fujimori, alkylation of the two auxochromic phenolic groups. A brief NMR study, however, was unable to shed any light on the mechanism of the interaction.