Enantiomeric Separation of Free l- and d-Amino Acids in Hydrolyzed Protein Fertilizers by Capillary Electrophoresis Tandem Mass Spectrometry

Two capillary electrophoresis–tandem mass spectrometry (CE–MS2) methods were optimized in this work using cyclodextrins (CDs) as chiral selectors in order to determine the degree of racemization of the free amino acids contained in different hydrolyzed protein fertilizers used as plant biostimulants. The methodologies developed were characterized by the specificity of MS2 experiments enabling the identification of all protein amino acids, except for cysteine. The enantiomeric separation of up to 14 amino acids was achieved with resolutions above 1.0 and limits of detection between 0.02 and 0.8 μM. The methods were applied to the analysis of complex samples such as hydrolyzed protein fertilizers to evaluate the presence of d-amino acids after different kinds of hydrolysis treatments. The results corroborated the absence or almost negligible presence of enantiomeric conversions of the l-amino acids into d-amino acids in the case of fertilizers obtained by enzymatic hydrolysis, as well as the high racemizati...