Using a Smartphone for Determining Tetracyclines in Water and Milk by the Sensitized Solid State Fluorescence of Europium on Its Hydroxide

A possibility of determining antibacterial preparations of the tetracycline series (tetracycline, doxycycline, oxytetracycline, demeclocycline, methacycline and chlortetracycline) in waste water, natural waters, and milk by the sensitized fluorescence of europium on its hydroxide using digital colorimetry (smartphone) is studied. It is found that europium(III) forms complexes with tetracyclines in an alkaline medium, and the formation of the europium hydroxide precipitate does not change its fluorescence properties. The colorimetric parameters of the precipitate after centrifugation are measured using a smartphone. The limits of detection and determination are 0.001–0.004 and 0.005–0.01 µg/mL, respectively, for all analytes. The analytical ranges are 0.005 (0.08)–0.1 (1) µg/mL. The calibration curves are linear, R2 ≥ 0.98. A procedure for determining the total concentration of tetracyclines in waste water, natural waters, and milk is proposed. The duration of analysis is 20–30 min; the relative standard deviation of the results of analysis does not exceed 20%.