HPLC−MS/MS Profiling of Tryptophan-Derived Alkaloids in Food:  Identification of Tetrahydro-β-carbolinedicarboxylic Acids

A method for selective detection of 1,2,3,4-tetrahydro-β-carbolinecarboxylic acids (THCCs) was developed based on electrospray ionization−tandem mass spectrometry coupled to liquid chromatography (HPLC−ESI−MS/MS). Low-energy collision-induced dissociation (CID) led to characteristic fragment ions due to neutral loss of 73 amu. Subsequently, constant neutral loss scanning was used for substructure specific screening of THCCs in food samples. Detection limits for HPLC−ESI−MS/MS analysis of THCCs applying neutral loss experiments were established at 100 ng mL-1 (ca. 2.5 pmol on column). Application of this MS/MS method enabled us to detect THCC derivatives derived from Pictet−Spengler condensation of tryptophan with α-oxo acids. Subsequently, diastereomeric 1,2,3,4-tetrahydro-β-carboline-1,3-dicarboxylic acid 3a/b, 1-methyl-1,2,3,4-tetrahydro-β-carboline-1,3-dicarboxylic acid 4a/b, and 1-(2‘-carboxyethyl)-1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid 5a/b were identified in alcoholic beverages, seasoning sauces, yeast extract, and fruit products for the first time. Most food samples under study contained 3a/b and 4a/b in significant amounts. 5a/b was identified in soy sauce, worcestershire sauce, seasoning sauce, and yeast extract. Due to the excellent selectivity of tandem mass spectrometry coeluting tetrahydro-β-carboline derivatives could be identified unequivocally by HPLC−ESI−MS/MS. Keywords: Tetrahydro-β-carboline; electrospray ionization; tandem mass spectrometry; neutral loss scanning