Determination of Linezolid in Human Plasma Using Turbulent Flow Online Extractionand Tandem Mass Spectrometry

A rapid and sensitive HTLC-ESI-MS/MS method was developed for the determination of Linezolid in human plasma using an internal standard (cetirizine hydrochloride) with an advanced online sample preparation. This HTLC technique reduces the time required for sample cleanup since sample extraction and analysis are performed. A 10μl of prepared sample is directly injected into the HTLC-MS/MS system where analyte was retained on the extraction column (Cyclone P 50 × 0.5mm, 50μm) and washed away the waste with the help of extraction solvent. Then the analyte was eluted from the extraction column and transferred to the analytical column (Zorbex XDB C18 50 × 2.1mm, 5μm) using mobile phase of the mixture of 0.5% formic acid, 10mM ammonium formate and acetonitrile. The eluted analyte was then detected on mass spectrometer with ESI ion source and a positive selective reaction monitoring mode (SRM). The SRM transitions were m/z 383.20 → 337.20 for Linezolid and m/z 389.10 → 201.01 for internal standard. The developed method was validated as per USFDA guidelines. The method was linear over the concentration range of 0.409 – 20.310 ng/ml. The within batch and between batch accuracy for the three concentrations (LQC, MQC and HQC) were ranged from 98 -110.6% and 98 .6 – 108.3% respectively. The % RSD for all the QC samples was ranged from 3.0 – 8.1%. The percentage recovery of linezolid in HQC (16ng/ml), MQC (13ng/ml) and LQC (1,1ng/ml) was 60.3, 73 and 86.45% respectively. Stability studies were also performed and the results were within the acceptance range. This method was applied to the measurement of linezolid in human plasma and pharmacokinetic study.