Electrochemical Characterization and Voltammetric Determination of beta-N-oxalyl-L-alpha,beta-diaminopropionic Acid in Grass Pea Seeds

Abstract

The oxidation of the neurotoxic amino acid, beta-N-oxalyl-L-alpha,beta-diaminopropionic acid was characterized by cyclic and square-wave voltammetries on a glassy carbon electrode. An electrochemical protocol was developed and validated for the determination of beta-N-oxalyl-L-alpha,beta-diaminopropionic acid in grass pea seeds. Solid-phase extraction was used to separate homoarginine while simultaneously eluting and presenting similar electrochemical behavior amino acid. The analyte, beta-N-oxalyl-L-alpha,beta-diaminopropionic acid, exhibited a prewave and a quasireversible anodic peak at 147 mV (prewave) and 200 mV (oxidation peak) versus Ag/AgCl in 0.10 M phosphoric acid buffer at pH 3.0. The oxidation of beta-N-oxalyl-L-alpha,beta-diaminopropionic acid was proceeded by adsorption on a glassy carbon electrode by two steps involving two electrons and one hydrogen ion transfer via a quasireversible electrode mechanism. The rate constant was calculated using the quasireversible maximum. The beta-N-oxalyl-L-alpha,beta-diaminopropionic acid was electropolymerized on the carbon electrode surface to form poly-beta-N-oxalyl-L-alpha,beta-diaminopropionic acid by cyclic voltammetry, analogous to glutamic acid. A linear dependence of the peak current with concentration was observed from 1.20 to 44.6 mu M with a detection limit of 1.28 mu M using square-wave adsorptive stripping voltammetry and accumulation at -0.4 V versus Ag/AgCl for 60 s. The glassy carbon electrode was cleaned by photocatalytic pretreatment, and the results were compared with alumina polishing. The method was used to analyze grass pea seeds with good specificity and accuracy.