Behavior and characteristics of amine derivatives obtained with o-phthaldialdehyde/3-mercaptopropionic acid and with o-phthaldialdehyde/N-acetyl-L-cysteine reagents

A comprehensive evaluation of papers dealing with the HPLC quantitation of amines as o-phthaldialdehyde (OPA) derivatives has been given and discussed in details. The stability and characteristics of selected representatives of mono [methyl-, ethyl-, n-/isopropyl, n-/isobutyl-, tert.-butyl-, sec.-butyl-, isoamyl amines and ethanolamine), di- and polyamines (ethylenediamine, 1,2-propylenediamine, 1,3-propylenediamine, agmatine, tyramine, putrescine, cadaverine, histamine, spermine, spermidine, and bis(hexamethylene)triamine] have been investigated as their OPA/3-mercaptopropionic acid (MPA) and OPA/N-acetyl-L-cysteine (NAC) derivatives, from an analytical point of view, performing photodiode array and fluorescence detection, simultaneously. All amines having in their original structure the NH2-CH2-R moiety, in accord with the amino acids of the same structure, furnished more than one OPA derivative: their initially formed species transformed to further ones. On the basis of on-line HPLC-MS the transformed derivatives were proved to be the corresponding isoindoles that contain an additional OPA molecule. In order to achieve optimum analytical conditions derivatization reagents have been applied in different composition, in parallel. The OPA and the SH-group additive contents of the reagents have been varied in the mole ratios of OPA/MPA(NAC)=1:3 and OPA/MPA(NAC)=1:50. Data obtained proved that performing derivatizations by means of the OPA/MPA(NAC)=1:50 reagents resulted in two benefits: both the stability of derivatives could have been increased and the number of the transformed derivatives decreased. In case of aliphatic amines and in ethanolamine, the transformation of the initially formed derivative can be either quantitatively avoided as in the case of ethanolamine, or considerably decreased, below 1%, as in the cases of the other aliphatic monoamines investigated. As to the behavior of di- and polyamines the stability of derivatives has been considerably improved, the number of species have been decreased from four to two with the exception of spermidine. Stability values characterized both by the UV and fluorescence responses, as a function of the reaction time (from 90 s up to 6 h) have been given in details.