Electrochemical analysis of the alanine phenylthiohydantoin derivative by cathodic stripping voltammetry

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 × 10−8 − 4.8 × 10−7 M range, with a LOD of 1.2 × 10−8 M and a LOQ of 4.2 × 10−8 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.