Voltammetric determination of tryptophan at a single-wall carbon nanotubes modified electrode.

A single-wall carbon nanotubes (SWNT)-film coated glassy carbon electrode (GCE) was described for the determination of tryptophan. In pH 2.5 Na2HPO4-citric acid buffer, tryptophan yields a well-defined and very sensitive oxidation peak at about 1.08 V at the SWNT-film coated GCE. The oxidation peak current increases greatly and the peak potential shifts toward more negative direction at the SWNT-modified GCE in contrast to that at the bare GCE. Under optimized conditions, the oxidation peak current is proportional to the concentration of tryptophan over the range from 4 x 10(-8) to 1 x 10(-5) mol/L. The detection limit is 1 x 10(-8) mol/L at 3 min of accumulation. Using the proposed method, tryptophan in the human's blood serum samples was determined.