Fluorescence quenching of the probes l-tryptophan and indole by anions in aqueous system

Abstract

A fluorescence quenching study of the fluorescent probes L-tryptophan and indole by anions (NO3-, Cl-, SO42-) was carried out in an aqueous system. The ions NO3-, Cl- and SO42- showed very good quenching of both the probes. Quenching of L-tryptophan by all the anions studied was higher as compare to the quenching of indole. The data was fitted with the Stern-Volmer equation. Stern-Volmer constants were observed in the order NO3- > Cl- > SO42-. Stern-Volmer constants reflect the sensitivity of the method for the studied anions. Limit of detection (LOD) was calculated as three times the standard deviation of the blank for n = 10 (3 × SD) while the limit of quantification (LOQ) was calculated as ten times the standard deviation of the blank for n = 10 (10 × SD). In the case of L-tryptophan LOD and LOQ varied from 4.08 × 10-5 - 4.56 × 10-4 mol L-1, while in the case of indole the values ranged from 3.87 × 10-5 - 6.59 × 10-4 respectively. Fluorescence quenching of L-tryptophan and indole by the studied anions showed good reproducibility and the method could be very effective for the determination of anions.