Determination of 5-hydroxytryptophan in plasma by high-performance liquid chromatography and fluorometric detection after phthaldialdehyde reaction.

We describe the sensitive and precise determination 5-hydroxytryptophan in plasma from patients treated with this compound. The method is based on solvent extraction of plasma, high-performance liquid chromatography and continuous fluorometric detection after reaction with phthaldialdehyde in strong acid. The combined time for chromatography and reaction is 25 min. The sensitivity of the method is adequate to quantitate 0.05 mumol of 5-hydroxytryptophan per liter, in 750 microliter of plasma. No interference by other hydroxyindole compounds was found.