Metal Complex-Based Fluorescent Probe for Sensitive Determination of Citric Acid in Food Samples via a Ligand-Exchange Reaction: An Innovative and Sustainable Approach.

A novel, rapid, and eco-friendly spectrofluorimetric method was developed and validated for the sensitive determination of citric acid in food samples using an iron(III)salicylate metal complex as a fluorescent probe. The method may involve a possible ligand-exchange process, in which citric acid preferentially coordinates with iron(III), potentially releasing free salicylate and resulting in a marked increase in fluorescence intensity at 409 nm upon excitation at 295 nm. Experimental parameters, including reagent concentration, pH, solvent type, and reaction time, were systematically optimized to maximize sensitivity. The method was validated according to ICH guidelines, showing excellent linearity over 0.2-4.0 µg/mL (r = 0.9999) and low detection and quantitation limits of 0.028 and 0.086 µg/mL, respectively. High accuracy, precision, robustness, and selectivity were achieved, with no significant interference from common food constituents. Practical applicability was demonstrated through successful determination of citric acid in juice, cola, and ice cream using the standard addition technique. Sustainability assessment using ComplexGAPI, AGSA, and MA tools indicated a favorable environmental profile, as it employs only distilled water, minimizes hazardous organic solvents, avoids heating and complex sample preparation, making it suitable for routine food analysis.