Solid-phase luminescence determination of tetracycline in bottled water using chemically modified silica

Possibility of using chemically modified silica (CMS) with covalently immobilized sulfonic and ethylenediaminetriacetate (ED3A) groups for the adsorption preconcentration and extraction of tetracycline (TC) from aqueous solutions is studied. The conditions of complex formation by europium(III) ions on the surface of these adsorbents are optimized. The effect of citrate and Eu3+ ions on the luminescence intensity of the Eu–TC complex is shown. The luminescence properties of SiO2ED3AEu and SiO2SO3HEu systems with tetracyclines are studied depending on the acidity of the medium, time of phase contact, the ratio of the volume of the solution to the weighed portion of the adsorbent, and concentrations of the adsorbed substances. It is found that tetracycline is quantitatively extracted by CMS as a complex with europium(III) ions in pH range 6.5–8.0; adsorption capacity to tetracycline in the Henry region is as high as 0.07–0.09 mmol/g and partition coefficients are 103–104 mL/g. A procedure is developed for the solid-phase luminescence determination of tetracycline using SiO2SO3HEu and SiO2ED3AEu systems with limits of detection of 0.8 and 2.0 nM, respectively; linearity range is 1 × 10–9–1 × 10–5 M. The procedure is tested in the analysis of model mixtures and samples of bottled water.