A surrogate analyte-based LC-MS/MS method for the determination of 5-hydroxytryptamine, kynurenine and tryptophan

Aim: The metabolism of tryptophan (TRP) through kynurenine (KYN) and 5-hydroxytryptamine (5-HT) pathways is linked to various diseases such as neurological diseases and cancer. The levels of 5-HT, KYN, TRP can be used as indicators for the diagnosis of various diseases in clinical and scientific research. Experimental: Since 5-HT, KYN, TRP are both endogenous molecules in biological samples, it is difficult to obtain a 'real blank sample'. A surrogate analyte-based LC-MS/MS method was chosen, using 5-HT-d4, KYN-d4 and TRP-d5 as surrogate analytes to replace the authentic analytes 5-HT, KYN and TRP, respectively. Theophylline was selected as the internal standard (IS). Results: The method was applied to quantification 5-HT, KYN and TRP of plasma, liver, colon, brain and verified to be acceptable in terms of linearity, precision, accuracy, matrix effect, recovery efficiency and stability.