Fluorometric Determination of Tryptophan and Its Brain Indoleamine Metabolites by Ion-Pair HPLC

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Abstract
The reverse phase HPLC separation of tryptophan, serotonin, 5-hydroxyindoleacetic acid, tryptamine and indoleacetic acid using two solvent systems (one of them containing an ion-pairing reagent) is reported. The two low concentration eluents employed are either formic acid/water or 0.005 mol/L solution of 1-pentane sulfonn ic acid. In both cases chromatographic separation was achieved through a linear gradient elution using methanol/water (7/3) as the high concentration eluent. We also describe the variation of retention volumes of these compounds as a function of the pH of the mobile phase. pH values ranged from 1.5 to 4.0 and were obtained by adding either formic acid or NaOH respectively to the low concentration eluent. Tryptophan and its metabolites were detected fluorometrically. All compounds show a linear response in the pg to μg range. The chromatographic separation achieved allows a concurrent measurement of tryptophan and its main indoleamine metabolites which coupled to the high sensitivity of fluorometric detection permits a direct estimation of these metabolic pathways in brain tissue.

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