Extraction-less Green Spectrofluorimetric Method for Determination of Mercury Using an Astra Phloxine Fluorophore: Comprehensive Experimental and Theoretical Studies

A new sensitive and selective extraction-less method for the spectrofluorimetric determination of Hg2+ has been developed using the polymethine dye Astra Phloxine (AP) with requirements for green analytical chemistry. The principle of this method for analytical use is the formation of an ion associate (IA) in the presence of mercury ions and AP, which causes a change in the electronic structure of the dye cation and its subsequent fluorescence quenching. The IA created during the process was sufficiently stable in aqueous solutions and did not require the use of surfactants or organic solvents, which are typically used for similar analytical systems. The system indicated high selectivity towards Hg2+ in the presence of at least 100-fold higher concentrations of Co2+, Fe2+, Mg2+, Ni2+, Zn2+, Ca2+, Ba2+, K+, Na+. The calibration curve was linear in the range from 0.003 to 0.1 mg L-1. Precision and accuracy were expressed as intra-day and inter-day analysis with RSD values of 2.9 - 4.8 % and recovery of 97.1 -110.0 %. The proposed method was used for the determination of Hg2+ on the model and real water samples. Theoretical calculations were used to predict the IA structure and to explain the experimentally observed fluorescence spectra. A few theoretical methods were tested for predicting IA emission energies, and the CIS(D) method was found to be the most accurate.