Quantitative determination of clozapine in plasma using an environmentally friendly technique

[Display omitted] •Clozapine is an effective atypical antipsychotic used when standard ones fail.•Sensitive analytical methods are needed as a low doses are administered.•DLLME allowed the extraction of clozapine within the toxic and therapeutic range.•GC/MS allowed the determination and quantification achieving good validation results.•Clozapine was determined alone with other drugs or drugs of abuse. A new method for the determination of clozapine in blood samples, a common antipsychotic drug, has been developed. It is based upon a dispersive liquid–liquid microextraction technique employed as the extraction method together with gas chromatography-mass spectrometry operating in selected ion monitoring (SIM). The method was fully validated including selectivity, sensitivity, accuracy, precision and recovery steps. The limit of quantification was set at 50 ng/mL. Intra and interday accuracy and precision values were lower than 17% at the concentration levels studied. Good recovery results were obtained for all concentrations. The proposed method was satisfactory applied to 10 plasma samples received at the Forensic Toxicology Service of the Forensic Science Institute of Santiago de Compostela, obtaining results within the therapeutic range. The results showed the usefulness of the analysis in any forensic toxicology laboratory and the posibility of determining clozapine in the presence of other drugs or drugs or abuse.