2.5. Preparation of stock solutions
A 1 mg/ml ciprofloxacin stock solution was initially prepared inmethanol. During analysis of this solution following storage for 1week, 2 peaks were noted. When compared to previous analysis ofthe same solution, after 1 week the first peak which representedciprofloxacin, decreased in size and a new peak was observed at alater retention time.In response to this, the stock solution was prepared using0.2 M hydrochloric acid. When the solution was analysed, peakshouldering was observed in the chromatogram. For this reason,ciprofloxacin was dissolved in the mobile phase. Working solu-tions were prepared from the stock solution by dilution with mobilephase. Sulfadimidine sodium was dissolved in HPLC-grade water tomaketomake up a stock solution of 1 mg/ml. All solutions were protectedfrom light and were stored at 4◦C.