Determination of L-tryptophan and L-kynurenine in Human Serum by using LC-MS after Derivatization with (R)-DBD-PyNCS

Concentrations of L-tryptophan (L-Trp) and its metabolite, L-kynurenine (L-KYN), in sera of 19 normal subjects (age: 23.6 ± 3.5 y, male: 8, female: 11) were determined by high-performance liquid chromatography with mass-spectrometric detection, following their derivatization with ( R)-(–)-4-(N, N-dimethylaminosulfonyl)-7-(3-isothiocyanatopyrrolidin-1-yl)-2,1,3-benzoxadiazole (DBD-PyNCS). A significant positive correlation between L-Trp and L-KYN concentrations was observed (r = 0.532, P < 0.05). Serum L-Trp concentration in male subjects (95.65 ± 4.27 μM) was significantly higher than that in female subjects (79.20 ± 3.34 μM; P < 0.05), while no significant differences in L-KYN concentration or the L-KYN:L-Trp ratio were observed between male and female subjects.