The analytical system was performed follow the United States
Pharmacopeia 35. The chromatographic procedure was carried out
using an Eclipse XDB-C18 column (5 mm, 4.6 mm 250 mm) [31].
The column was thermostates at 298.15 1 K using a column
heater. The flow rate of the mobile phase was 1.5 mL/min; injection
volume was 10 mL. The relative retention times of amoxicillin were
about 5.9 min as detected by a spectrophotometer set at UV 230 nm.
The analysis time was set at 25 min per sample to eliminate potential
interference from late eluting peaks. The pH of the aqueous phase was
measured with a SevenMultiTM modular pH meter with expansion
unit (Mettler-Toledo, Greifensee, Switzerland).