Spectrofluorimetric Method for Sensitive Histamine Detection Using Europium Complexation

A novel and rapid spectrofluorimetric method for histamine (HA) detection in food matrices was developed based on its complexation with europium-(III) chloride (EuCl₃) in an aqueous medium. Although histamine is intrinsically nonfluorescent, coordination with Eu³⁺ induces a strong characteristic red emission centered at 620 nm. The fluorescence response was markedly enhanced by optimizing the physicochemical parameters, particularly europium concentration and solution pH, which govern histamine protonation and complex stability. Under optimal conditions, a linear fluorescence response was obtained over the investigated concentration range, with an excellent correlation coefficient (R² = 0.9935). The limits of detection and quantification were determined to be 0.175 mg L^-1 and 0.576 mg L^-1, respectively. The method was fully validated in accordance with international guidelines, demonstrating good repeatability, reproducibility, and satisfactory recoveries (73-98%) when applied to real milk samples, with minimal matrix interference. Job's plot analysis revealed a 1:2 stoichiometry for the Eu-HA complex. Structural elucidation by ¹H NMR spectroscopy confirmed histamine coordination mainly through its amine and imidazole nitrogen atoms. Density Functional Theory (DFT) calculations supported the experimental findings, highlighting charge redistribution and ligand-to-metal charge transfer effects that contribute to the enhanced luminescence. These combined spectroscopic, analytical, and theoretical results demonstrate that europium-(III) complexation provides a simple, stable, and sensitive platform for histamine detection in food safety applications.