A capillary electrophoresis method with capacitively coupled contactless conductivity detection (CE-C4D) has been developed, optimized and validated for the determination of ciprofloxacin.
Ciprofloxacin is a member of the fluoroquinolone antibiotics with a broad spectrum bactericidal activity and recommended for complicated respiratory infections, sexually transmitted diseases, tuberculosis, bacterial diarrhea etc.
Method development was conducted with major focus on the quality by design (QbD) approach. During method development, multiple buffers were tried at different ionic strength. However, the optimized method finally involved a very simple background electrolyte, monosodium citrate at a concentration of 10 mM without pH adjustment.
The optimized CE-C4D method involved an uncoated fused silica capillary (59/39 cm, 50 μm i.d.) and hydrodynamic sample injection at a pressure of 0.5 p.s.i. for 5 s. The actual separation was conducted for 10 min at normal polarity with a voltage of 20 kV corresponding to 5.9 μA current. LiCl (1 mg/mL) was used as an internal standard.
The optimized method is robust and accurate (recovery >98%) which rendered the ciprofloxacin peak within five minutes with good linearity (R2 > 0.999) in the concentration range of 0.0126–0.8 mg/mL. The repeatability is expressed by percentage relative standard deviation (%RSD) of the relative peak areas (RPA) and it showed good repeatability both intra-day (<3%) and inter-day (3.1%). This method, proven to be free of matrix interference, showed that the estimated percent content of ciprofloxacin (102%) was within the official requirements.
Moreover, due to its ease of use and robustness, the method should also be applicable in less well controlled laboratory environments.