Adsorptive stripping voltammetric determination of tryptophan at an electrochemically pre-treated carbon-paste electrode with solid paraffin as a binder

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Abstract
An adsorptive stripping voltammetric method for the determination of tryptophan at an electrochemically pre-treated carbon paste electrode has been developed. Solid paraffin was used as the binder of the carbon paste. The electrode was pre-treated in a solution of HAc-NaAc (pH 3.5) by holding it at +1.8 V versus an Ag/AgCl electrode for 10 min. On the pre-treated electrode the adsorption of tryptophan was greatly enhanced. Tryptophan was accumulated in HAc–NaAc solution (pH 3.5) at a potential of +0.3 V versus an Ag/AgCl electrode for a certain time, and then determined by differential anodic stripping voltammetry. An oxidative peak was observed at +1.01 V. The relationship between peak current and tryptophan concentration was linear in the range 8–100 ng ml–1 of tryptophan, and the detection limit was 2 ng ml–1. The method has been applied to the determination of tryptophan in amino-acid compound injection and synthetic serum samples. The relative standard deviation (6 determinations) was less than 2%.

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