A simple, isocratic high-performance liquid chromatography assay for linezolid in human serum

A rapid high-performance liquid chromatography (HPLC) assay for the detection of linezolid in human serum was developed. The method used a Hypersil 5ODS stationary phase. The mobile phase was 1% ortho-phosphoric acid, 30% methanol, 2 g/L heptane sulphonic acid, pH 5. UV absorbance detection was used (lambda(max) 254 nm). Samples were prepared by mixing with acetonitrile and an injection volume of 20 microL was used. The inter- and intra-day assay reproducibility were assessed. Assay linearity, specificity and accuracy were investigated. The detection limit and recovery of linezolid from serum were determined. In addition, the stability of linezolid, stored under a variety of conditions, was assessed. The retention time of linezolid was c. 6.5 min. The intra- and inter-day reproducibility was good and the assay was linear across the therapeutic range. Serum recovery was c. 100% at all concentrations tested. The detection limit was 0.1 mg/L and the assay was accurate. The assay was specific as there was no significant interference with the linezolid peak. Linezolid was demonstrated to be stable. This rapid assay is ideal for busy clinical laboratories with basic HPLC equipment.