Quantitation of cotinine and its metabolites in rat plasma and brain tissue by hydrophilic interaction chromatography tandem mass spectrometry (HILIC-MS/MS).

In this work, we developed a sensitive method to quantify cotinine (COT), norcotinine (NCOT), trans-3'-hydroxycotinine (OHCOT) and cotinine-N-oxide (COTNO) in rat plasma and brain tissue, using solid phase extraction (SPE), hydrophilic interaction liquid chromatography (HILIC) and tandem mass spectrometry (MS/MS). The linear range was 1-100 ng/mL for each analyte in rat plasma and brain homogenate (3-300 ng/g brain tissue). The method was validated with precision within 15% relative standard deviation (RSD) and accuracy within 15% relative error (RE). Stable isotope-labeled internal standards (IS) were used for all the analytes to achieve good reproducibility, minimizing the influence of recovery and matrix effects. This method can be used in future studies to simultaneously determine the concentrations of COT and three major metabolites in rat plasma and brain tissue.