Analytical method for amoxicillin.

Amoxicillin concentrations were determined through separation analyses using high-performance liquid chromatography (HPLC), with tinidazole as an internal standard. The calibration curve for amoxicillin was over a concentration range of 0.5 to 20 μg/ml. The lower limit of quantification (LLOQ) was 0.5 μg/ml. The interday and intraday coefficients of variation (CVs) of quality control samples were 4.30% and 3.05%, respectively. In this study, free concentration of amoxicillin was not measured. Since the amount of protein binding of amoxicillin in neonates is low (about 10%) (22), it can be considered negligible in determining our target concentration.