Synthesis and application of a fluorescent molecular probe for rapid detection of sulfur dioxide residues in traditional Chinese herbs

A fluorescence method based on a “turn-on” rhodamine derivative fluorescent probe was developed for the detection of hydrogen sulfite ions and sulfur dioxide residues in sulfur-fumigated herbs. This method was realized through a well-known aldehyde-bisulfite addition reaction accompanied by a ring opening of spirolactam of probe molecule in pH 4. 8 aqueous ethanol media which resulted in a significant fluorescence and color change. The fluorescence enhancement was linearly proportional to the concentrations of bisulfite ranging from 0. 005 to 20 μmol/L with a correlation coefficient of 0. 998 5. The detection limit was low as to 2. 0 nmol/L and there was no interference with other familiar co-existing anions, cations and reducing reagents indicating high sensitivity and selectivity of the proposed method. In addition, the novel probe was successfully applied for the identification of sulfur dioxide residues in herbs with a satisfactory recovery in five real samples.