Determination of free-form of cocaine in rat brain by liquid chromatography–electrospray mass spectrometry with in vivo microdialysis

A rapid liquid chromatography–electrospray mass spectrometry (LC–ES-MS) method with in vivo microdialysis for the determination of free-form of cocaine (COC) in rat brain has been developed. A C18 column and a gradient elution were employed for the separation. The [M+H]+ (m/z=304) and a fragmented ion (m/z=182) were detected using positive ion mode detection. Selective ion monitoring was utilized for quantitative measurement. The linearity of this assay was good ranging from 0.01 to 1.0 μM (r2=0.999). The inter- and intra-day precisions showed relative standard deviations ranging from 1.0% to 3.3% and 1.0% to 3.6%, respectively. In addition, the detection of one COC metabolite, benzoylecgonine (BE), by this assay was also investigated. The linearity, precision, and detection limit associated with this method for BE were determined. The application of this newly developed method was demonstrated by examining the pharmacokinetics of COC in rat brain.