Direct determination of serotonin in gut lavage fluid by liquid chromatographic ion trap tandem mass spectrometry

Direct determination of serotonin (5-HT) in gut lavage fluid from patients examined due to various gastrointestinal complaints has been achieved. The method involves addition of 5-methoxytryptamine (5-CH3O-HT) internal standard, centrifugation, filtration and injection of the sample supernatant in a liquid chromatographic system coupled to an ion trap tandem mass detector. Electro-spray in positive mode was used to isolate and fragment the protonated ions [5-HT + H]+ and [5-CH3O-HT +H]+ signals 177 and 191 m/z, respectively. Quantification was carried out by extracting the ion fragment chromatograms at 160 and 174 m/z for 5-HT and 5-CH3O-HT, respectively. The relationship 5-HT/5-CH3O-HT was modelled by using a simultaneous design in order to estimate the optimal amount of internal standard to be added to the samples prior to quantification.