Fluorescein mercury(II) acetate and sodium fluorescein as reagents for thedetermination of bis(2-chloroethyl)sulfide by fluorescence quenching

Bis(2-chloroethyl)sulfide causes strong quenching of sodium fluorescein and fluorescein mercury(II) acetate fluorescence in alcoholic media. Sodium fl uorescein shows the greater promise as a reagent for its determination by f luorescence spectrometry with excitation at 366 nm and measurement at 518 n m. The results indicate a working range between about 3 x 10(-7) and 4.5 x 10(-5) mol l(-1) bis(2-chloroethyl)sulfide in propan-1-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-ble aching making it unsuitable for long-term application. The mechanism of the quenching is obscure but may involve protonation of the fluorescein, anhyd rous hydrogen chloride having a similar quenching effect or, from earlier w ork 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 i nteraction. (C) 1999 Elsevier Science B.V. All rights reserved.