Quantitative determination of neurotransmitters, metabolites and derivates in microdialysates by UHPLC–tandem mass spectrometry

The main objective of the present work is to study the time-course of rat brain neurotransmitters in vivo after an oral challenge with a nutritional ingredient or an external stimulus, such as a chemical agent. An ultrahigh performance liquid chromatography–tandem mass spectrometry method for the identification and quantification of neurotransmitters, metabolites and derivates in microdialysates from rat brain was previously developed. Betaine, glutamine, glutamic acid, gamma-aminobutyric acid, phosphocholine, glycerophosphocholine, cytidine 5ʹ-diphosphocholine, choline, acetylcholine, dopamine, norepinephrine, serotonin, tyrosine, epinephrine, tryptophan and 5-hydroxyindoleacetic acid were selected as analytes. The method involves direct injection of samples of microdialysates from rat brain onto the chromatographic equipment and quantification with a triple quadrupole mass spectrometer detector using an electrospray ionization interface in positive mode. The limits of detection ranged from 0.1 to 50 ng mL−1 and the limits of quantification from 0.3 to 200 ng mL−1. The inter- and intra-day variability were lower than 15%. Recovery rates ranged from 85% to 115%.