Simultaneous Determination of Tryptophan and 5-hydroxytryptophan in Dietary Supplements using Capillary Zone Electrophoresis and Capacitively Coupled Contactless Conductivity Detection

Serotonin is a neurotransmitter that plays several roles in human health, mainly related to well-being sensation and physiological processes. It is a metabolite of tryptophan and 5-hydroxytryptophan, which are used as dietary supplementation. A simple method was developed to separate these three compounds using capillary electrophoresis equipped with capacitively coupled contactless conductivity detection, where the optimized conditions were background electrolyte consisting of a 3.0 mol L-1 acetic acid solution pH 2.13, separation voltage at +27 kV, hydrodynamic injection at 11 kPa and 5.0 s, 40 cm (total) and 20 cm (effective) length fused-silica capillary (30 µm inner diameter). By using these conditions, complete resolution of these three compounds was achieved in less than 6 minutes with efficiencies higher than 8.6×104 plates m-1. The limits of quantification were 66 µmol L-1 for serotonin and tryptophan and 132 µmol L-1 for 5-hydroxytryptophan. The method was applied on the determination of tryptophan and 5-hydroxytryptophan in supplements, and on the evaluation of the stability of the formulations under forced degradation studies.