Determination of amoxicillin in human serum and plasma by high-performance liquid chromatography and on-line postcolumn derivatisation.

A high selective, sensitive and fast HPLC method developed for the determination in human serum and plasma. After protein precipitation with perchloric acid, an aliquot of the supernatant was neutralized by mixing it with sodium acetate solution and injected into a C18 HPLC column. Detection was done by a fluorescence detector after on-line postcolumn derivatisation with fluorescamine. The practical limit of quantification was 0.1 microgram/ml using 0.3 ml of plasma. Linearity was given in the tested range of 0.1 to 15 micrograms/ml plasma. Inter-day precision (relative standard deviation) over 7 days for 0.42 micrograms/ml was +/- 7.27%; for 4.54 micrograms/ml, +/- 5.24% and for 13.18 micrograms/ml, +/- 5.25%. Stability over 50 days in serum and plasma occurs at -70 degrees C but not at -20 degrees C (-25 to -35% reduction). This method was used for thousands of human serum and plasma samples.