Detection of hydrogen sulfide in water samples with 2-(4-hydroxyphenyl)-4,5-di(2-pyridyl)imidazole-copper(II) complex using environmentally green microplate fluorescence assay method

Hydrogen sulfide (H₂S) is a colorless toxic gas which can be found as HS^- in rivers and waste waters especially in the occupational susceptible environment. Herein we synthesized a lophine analogue, 2-(4-hydroxyphenyl)-4,5-di(2-pyridyl)imidazole (HPI), which fluoresces at 410 nm after excitation at 280 nm. HPI has an imidazole ring and a pyridine ring which are capable of forming coordinate bonds with copper (Cu(II)) that cause quenching of HPI fluorescence. We found that HS^- can selectively liberate HPI from the complex via formation of CuS, thus, HPI regains its fluorescence properties. Interestingly, the probe was proved to be regenerable. This reaction was used for the development of a fluorescence microplate assay for the determination of HS^- in environmental samples. The method was applied to river water samples and was able to detect HS^- in concentrations down to 5 ppb with acceptable accuracy (90.3-103.0%) and good precision (%RSD ≤ 4.1). The method showed many advantages over the previously reported ones including instantaneous reaction, simple probe synthesis, high-throughput, high selectivity toward hydrogen sulfide over other ions and sulfur or thiol containing compounds and at last, it complies with the green chemistry rules through using a regenerable probe, aqueous solvents, and miniaturized measurement system.

Copper; Fluorescence microplate assay; Hydrogen sulfide; Lophine analogue; River water.