Selective recognition of Cr3+ in multivitamin formulations in aqueous medium by fluorescent organic–inorganic nanohybrids

Abstract

An effective method for the detection of Cr3+ in multivitamin formulations has been developed by using fluorescent organic nanoparticles (FONPs) based on N,N′-bis(5-bromothiophen-2-ylmethyl)ethylenediimine (BTED). In the study, FONPs selectively recognize Cr3+ without inferring other coexisting metal ions in the medium. Since the FONPs enhance the fluorescence intensity with respect to the concentration of Cr ion, they were applied in real samples like multivitamin formulations to detect Cr3+. The stoichiometry of FONPs/Cr3+ analyzed by a Job’s plot was 2:1 (FONPs:metal). The results show that FONPs accurately measure the concentration of Cr3+ in the vitamin tablets in aqueous medium, agreeing with the reported chromium content in the vitamin formulations, and the detection limit was found to be 7.2 μM. Furthermore, the binding nature of the ligand with Cr3+ was studied through the molecular orbital analysis, where a lower energy HOMO was observed for [Cr(BTED)]3+ than that for the free ligand, meaning that the lowering of the receptor HOMO energy enhances the fluorescence emission in the photoinduced electron transfer.