Pressure-assisted electrokinetic injection stacking for seven typical antibiotics in waters to achieve μg/L level analysis by capillary electrophoresis with UV detection

Abstract

An effect sensitive CE method for the analysis of four fluoroquinolones (FQs) antibiotics (ofloxacin (OFL), enrofloxacin (ENR), ciprofloxacin (CIP) and norfloxacin (NOR)) and three sulfonamides (SAs) antibiotics (sulfamethazine (SMZ), sulfamethoxazole (SMX) and sulfadiazine (SDI)) in waters was developed by using pressure-assisted electrokinetic injection (PAEKI) stacking technique. The optimal background electrolyte (BGE) was 25.0 mmol/L Na2B4O7, 15.0 mmol/L methyl-β-cyclodextrin (M-β-CD) at pH 10.0 (adjusted by 1.0 mol/L NaOH). The addition of M-β-CD made significant contributions to the separation of OFL, CIP, and NOR, otherwise they co-migrated due to the similar electrophoretic mobilities in the borate buffer. To avoid a cumbersome optimization process of PAEKI, we built a simple method to determine the balance conditions. Herein, the applied voltage and external pressure values to immobilize the bulk flow of BGE could be clearly read from two curves of the BGE velocity respectively induced by pressure and electroosmotic flow (EOF). Under the selected injection condition during PAEKI (0.2 psi vs. −5.2 kV), the sample injection time could sustain 3.0 min without compromising separation efficiency. The sensitivity was improved to 75–110 times in comparison with normal hydrodynamic injection (HDI) mode. The obtained LODs (S/N = 3) of seven antibiotics were in the range of 1.96–4.06 μg/L at UV detection (272 nm), which approached the level of the antibiotics analyzed by CE with fluorescence detection. The precision was characterized by the RSDs of migration times and peak areas, which were averaged at 0.84% and 5.8% for the proposed PAEKI method. Finally, the recoveries of PAEKI were investigated at 83.3–98.7% by spiking FQs and SAs in the actual lake water of Donghua campus to illuminate its feasibility.