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

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%.