A selective dispersive liquid-liquid micro-extraction technique for trace level pollutants enrichment of pharmaceutical residues from hospital wastewaters followed by liquid chromatographic analysis

In this study a dispersive liquid-liquid micro-extraction (DLLME) method was utilized for extraction of trace pharmaceuticals in wastewater samples. Factors influencing the extraction performances were tested and accordingly 900 µL dichloroethane as the extraction solvent, 1400 µL acetonitirle as dispersive solvent, 10 min extraction time at 4000 rpm centrifugation, and pH 5 were found optimum. Acetonitrile and 0.2% formic acid in water were used as eluent. The column temperature was maintained at 25 °C and the optimum detection wavelengths of 273 nm for sulfamethoxazole and 280 nm for ciprofloxacin were used. For both the analytes, the coefficients of determinations (r2) were found to vary from 0.9989 to 0.9997, confirming good linearity in the concentration range of 0.005-100 µg mL-1 for sulfamethoxazole and 0.01-100 µg mL-1 for ciprofloxacin. The LOD and LOQ were in the range of 0.78-1.58 ng mL-1 and 2.24-5.28 ng mL-1, respectively; the RSDs were 0.41-3.21% for intra-day precision and 0.37-6.44% for inter-day precision. The concentrations of the three pharmaceuticals determined ranged from 0.76-1.53 μg mL-1 in the wastewater samples collected from Black Lion Hospital. However, ciprofloxacin and doxycycline were not detected and only low concentration of sulfamethoxazole was detected in the wastewater samples collected from Menelik II Hospital. KEY WORDS: Antibiotics, DLLME, Dispersive solvent, Hospital wastewater Bull. Chem. Soc. Ethiop. 2024, 38(1), 27-42. DOI: https://dx.doi.org/10.4314/bcse.v38i1.3