A filtration optimized on-line SPE–HPLC–MS/MS method for determination of three macrolide antibiotics dissolved and bound to suspended solids in surface water

Abstract

In this work, a simple, automated multiresidue method consisting of on-line solid phase extraction coupled to liquid chromatography tandem mass spectrometry has been developed for the determination of three macrolide antibiotic residues – erythromycin, clarithromycin and azithromycin – included in the current Watch List (Decision 2018/840) of Water Framework Directive of the European Union in surface water. Due to the possible losses of target analytes, the effect of filtration on their concentrations was evaluated in terms of the filter material and pore size. Thus, glass fiber-nylon (0.45 μm and 0.22 μm pore sizes), 0.2 μm pore size nylon and 0.2 μm pore size polyvinylidene difluoride filters were used. As the Directive (2008/105/EC) prescribes the whole water monitoring, both the filtrate and solid fraction were analyzed. To estimate the analyte losses arisen from the adsorption on the solid phase, elution of the loaded filter with different aliquots of acetonitrile was also studied. The most suitable filter was the nylon of 0.2 μm pore size one, ensuring recoveries >80% for all three target analytes. By washing the filter with 2 mL acetonitrile, about 100% recovery rate was achieved for each macrolide in ultrapure water as well as river water spiked to 200 μg L−1 for each target analyte. The proposed sample pre-treatment protocol was successfully applied for the analysis of Danube River samples by using the internal standard calibration method. In one sample taken nearby a wastewater treatment plant, a relatively high concentration of clarithromycin (68 ± 0.4 ng L−1) was found.