A square-wave cathodic stripping voltammetry method for alanine determination as its phenylthiohydantoin
(PTH-alanine) derivative is developed. To this end, all the chemical and instrumental variables
affecting the determination of PTH-alanine are optimized. From studies of the mechanisms governing
the electrochemical response of PTH-alanine, it was concluded that it is an electrochemically irreversible
system with a diffusive-adsorptive reduction phenomenon. Under optimal conditions, the variation of
analytical signal (Ip) with PTH-alanine concentration is linear in the 2.4 108 4.8 107 M range,
with a LOD of 1.2 108 M and a LOQ of 4.2 108 M, a RSD (%) less than 11%, and a Er (%) less than
10%. The optimized method was applied to the determination of PTH-alanine obtained from a synthetic
protein after Edman reaction and the results were corroborated by high-performance liquid chromatography
with UV detection.