Derivatization, stability and chromatographic behavior of o-phthaldialdehyde amino acid and amine derivatives: o-phthaidialdehyde/2-mercaptoethanol reagent

A literature overview is given of HPLC methods currently in use to determine amino acids (AAs) and amines (As) as their o-phthaldialdyde (OPA)/2-mercaptoethanol (MCE) derivatives. This is followed by an exhaustive derivatization study performed using the classical proteinogen AAs, C-1 - C-4 aliphatic As, several polyamines (PAs) and the OPA/MCE reagent. Model studies have been carried out as a function of reaction time and reagent composition. The primary importance of reagent composition (mole ratios of OPA to SH-group additive) is repeatedly proven. Stabilities of the OPA/MCE derivatives have been compared with corresponding OPA/3-mercaptopropionic acid (MPA) and/or OPA/N-acetyl-L-cysteine (NAC) compounds, obtained under the same conditions. Crucial factors proven to influence the stability of OPA derivatives of AAs and As are discussed in detail: (i) preparation and storage conditions of the OPA reagents, (ii) special behavior of the currently believed to be particularly unstable, AAs and As associated with their original molecular structure, e.g. glycine, beta-alanine, gamma-amino butyric acid (GABA), histicline, ornithine and lysine, several As, as well as (iii) the mole ratios of the OPA/SH-additive/AA and/or A.