Colorimetric and fluorescent determination of sulfide and sulfite with kinetic discrimination

Two fluorescent probes, m-PSP and p-PSP, for sulfite and/or sulfide were constructed by connecting a pyridinium ion to a coumarin fluorophore through an α,β-unsaturated ketone. The presence of the pyridinium salt promoted the nucleophilic addition of sulfite and sulfide to the α,β-unsaturated ketone, which could be visualized by dramatic changes in the solution's color and fluorescence intensity. Both probes exhibit good selectivity (the selectivity coefficients toward major interferences are less than 0.07) and high sensitivity for sulfite and sulfide over biothiols and other potential analytes. The detection limits of m-PSP for the analysis of sulfite and sulfide are calculated to 8.5 × 10−7 M and 2.7 × 10−7 M, respectively. Living cell imaging results indicate that both probes can be applied in biological systems.