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-. 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.

Phenanthrene Fluorescence Quenching in Aqueous Sodium Dodecyl Sulphate (SDS) and Determination of Important Metal Ions.

In this work fluorescence quenching of phenanthrene by heavy metal ions (Fe3+, Cu2+, Cr3+ Pb2+, Ni2+) was studied in aqueous solution of sodium dodecyl sulphate (SDS). Fluorescence quenching was higher in lower SDS concentration and decreased with the increase in SDS concentration. Phenanthrene quenching by heavy metal ions were explained by Stern-Volmer equations and the Stern-Volmer constants were observed in the order Fe3+ > Cu2+ > Cr3+ > Pb2+ > Ni2+ respectively. Stern-Volmer constants reflect the sensitivity of the method for the studied metal ions. Limit of detection which was calculated as three time standard deviation of the blank for n = 10 (3×SD) ranged from 1.504×10-6-1.113×10-5 molL-1and limit of quantification which was calculated as ten times standard deviation of the blank for n = 10 (10×SD) ranged from 5.013×10-6-3.371×10-5 mol L-1. Phenanthrene fluorescence quenching by the studied metal ions shows good reproducibility and the used of anionic surfactant increases the fluorescence quenching of phenanthrene by heavy metal ions. This method could be very effective for the determination of metal ions.