Fluorescence Quenching of the Probes L-Tryptophan and Indole by Anions in Aqueous System

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-. Stem-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 x SD) while the limit of quantification (LOQ) was calculated as ten times the standard deviation of the blank for n = 10 (10 x SD). In the case of L-tryptophan LOD and LOQ varied from 4.08 x 10(-5 )- 4.56 x 10(-4) mol L-1, while in the case of indole the values ranged from 3.87 x 10(-5) - 6.59 x 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.