A rapid and simple method for the simultaneous determination of four endogenous monoamine neurotransmitters in rat brain using hydrophilic interaction liquid chromatography coupled with atmospheric-pressure chemical ionization tandem mass spectrometry.

Endogenous monoamine neurotransmitters play an essential role in neural communication in mammalians. Many quantitative methods for endogenous monoamines have been developed during recent decades. Yet, matrix effect was usually a challenge in the quantification, in many cases asking for tedious sample preparation or sacrificing sensitivity. In this work, a simple, fast and sensitive method with no matrix effect was developed to simultaneously determine four endogenous monoamines including serotonin, dopamine, epinephrine and norepinephrine in rat brain tissues, using hydrophilic interaction liquid chromatography coupled with atmospheric-pressure chemical ionization tandem mass spectrometry. Various conditions, including columns, chromatographic conditions, ion source, MS/MS conditions, and brain tissue preparation methods, were optimized and validated. Pre-weighed 20mg brain sample could be effectively and reproducibly homogenized and protein-precipitated by 20 times value of 0.2% formic acid in cold organic solvents (methanol-acetonitrile, 10:90, v/v). This method exhibited excellent linearity for all analytes (regression coefficients>0.998 or 0.999). The precision, expressed as coefficients of variation, was less than 3.43% for intra-day analyses and ranged from 4.17% to 15.5% for inter-day analyses. Good performance was showed in limit of detection (between 0.3nM and 3.0nM for all analytes), recovery (90.8-120%), matrix effect (84.4-107%), accuracy (89.8-100%) and stability (88.3-104%). The validated method was well applied to simultaneously determine the endogenous serotonin, dopamine, epinephrine and norepinephrine in four brain sections of 18 Wistar rats. The quantification of four endogenous monoamines in rat brain performed excellently in the sensitivity, high throughput, simple sample preparation and matrix effect.