Direct‐injection high performance liquid chromatography ion trap mass spectrometry for the quantitative determination of olanzapine, clozapine and N ‐desmethylclozapine in human plasma

A specific and sensitive direct‐injection high performance liquid chromatography electrospray ionization tandem mass spectrometry (HPLC/ESI‐MS/MS) method has been developed for the rapid identification and quantitative determination of olanzapine, clozapine, and N ‐desmethylclozapine in human plasma. After the addition of the internal standard dibenzepin and dilution with 0.1% formic acid, plasma samples were injected into the LC/MS/MS system. Proteins and other large biomolecules were removed during an online sample cleanup using an extraction column (1 × 50 mm i.d., 30 µm) with a 100% aqueous mobile phase at a flow rate of 4 mL/min. The extraction column was subsequently brought inline with the analytical column by automatic valve switching. Analytes were separated on a 5 µm Symmetry C18 (Waters) analytical column (3.0 × 150 mm) with a mobile phase of acetonitrile/0.1% formic acid (20:80, v/v) at a flow rate of 0.5 mL/min. The total analysis time was 6 min per sample. The inter‐ and intra‐assay coefficients of variation for all compounds were <11%. By eliminating the need for extensive sample preparation, the proposed method offers very large savings in total analysis time. Copyright © 2002 John Wiley & Sons, Ltd.