Factorial design-aided study of different fluorogenic approaches for determination of the preservative natamycin in various matrices

Abstract

Natamycin (NATA) is a widely used food preservative. It is a non-fluorescent compound; hence, a derivatization reaction to produce a fluorescent derivative was necessary for its analysis. In this context, two derivatization reactions were applied to develop two spectrofluorimetric methods for determining NATA. Method I relies on Hantzsch condensation reaction between the primary amine group of NATA and acetylacetone-formaldehyde (AAF) reagent to produce a highly fluorescent dihydropyridine derivative that is measured at λem/λex of 481/415 nm, while Method II based on the reaction of the primary amine group of NATA with o-phthalaldehyde in the presence of N-acetylcysteine which resulted in isoindole fluorophore derivative that can be monitored at λem/λex of 433/338 nm. The experimental variables of both methods were optimized using full-factorial designs. Under the optimum conditions, the proposed methods enabled the determination of NATA over concentration ranges of 50.0–500.0 ng mL−1 (LOD = 13 ng mL−1) for Method I and 0.50–10.0 μg mL−1 (LOD = 0.16 μg mL−1) for Method II. Both methods were efficiently applied to assay NATA in ophthalmic eye drops. The application was extended to include bread and environmental water samples based on the nano-scale sensitivity of Method I.