Development and validation of a solid-phase extraction-liquid chromatographic method for determination of amoxicillin in plasma

A bioanalytic method for the determination of amoxicillin in plasma by hydrophilic interaction solid-phase extraction and liquid chromatography has been developed and validated. Plasma was precipitated with acetonitrile before samples were loaded onto a zwitterionic hydrophilic interaction liquid chromatography (ZIG HILIC) solid-phase extraction column. Amoxicillin was analyzed by liquid chromatography on an Aquasil (150 X 4.6 mm) LC column with mobile-phase acetonitrile: phosphate buffer (pH 2.5; 0.1 mol/L) (7:93, nu/nu\) and UV detection at 230 nm. A regression model using 1/concentration(2) weighting was found the most appropriate for quantification. The intraassay precision for plasma was 3.3% at 15.0 mu g/mL and 10.9% at 0.200 mu g/mL. The interassay precision for plasma was 1.8% at 15.0 mu g/mL and 7.5% at 0.200 mu g/mL. The total-assay precision for plasma over 4 days using a total of 20 replicates was 13.2%, 5.5%, and 3.8% at 0.200 mu g/mL, 3.00 mu g/mL, and 15.0 mu g/mL, respectively. The lower limit of quantification and the limit of detection were 0.050 mu g/mL and 0.025 mu g/mL, respectively, for 100 mu L plasma. Long-term storage stability studies of amoxicillin in plasma indicate that a temperature of -80 degrees C is necessary to prevent degradation of amoxicillin.