Solid-Phase-Fluorimetric Determination of Quinolones in Medicinal Preparations on Cellulose Paper and in a Thin Silica Layer Using a Smartphone

A simple and an available method is proposed for the determination of quinolone antibiotics using solid-phase fluorescence digital colorimetry. The intrinsic fluorescence of 17 quinolones and the quinolone-sensitizedfluorescence of europium on cellulose paper (CP) and a thin silica layer are studied. Upon the irradiation of quinolone solutions applied to a matrix with ultraviolet light (365 nm), blue (CP, high-performance thin-layer chromatography (HPTLC)) and pink (CP–Eu, HPTLC–Eu) fluorescence is observed. Measurement of the fluorescence intensity on the surface of matrices is carried out using a smartphone. The values of colorimetric parameters in the RGB system are used as the analytical signal (Ar): Ar =  $$\sqrt {{{{({{{\text{R}}}_{0}} - {{{\text{R}}}_{{\text{x}}}})}}^{2}} + {{{({{{\text{G}}}_{0}} - {{{\text{G}}}_{{\text{x}}}})}}^{2}} + {{{({{{\text{B}}}_{0}} - {{{\text{B}}}_{{\text{x}}}})}}^{2}}} .$$ The limits of detection and determination are 0.2–4 and 0.6–12 µg/mL, respectively, for all analyzed analytes. The analytical ranges are 0.6–500 µg/mL. A procedure for the determination of fluoroquinolones in medicinal preparations is proposed. The relative standard deviation of the results of analysis does not exceed 5%.