Enantioseparation of the constituents involved in the phenylalanine-tyrosine metabolic pathway by capillary electrophoresis tandem mass spectrometry

- A CE-ESI-MS2 method is developed to determine Phe-Tyr metabolic pathway enantiomers.
- First simultaneous enantioseparation of the constituents of this metabolic pathway.
- Large volume sample stacking enabled to obtain LODs from 40 to 150 nM.
- Plasma samples were analyzed and L-Phe and L-Tyr were determined at μM level.

Catecholamines dopamine, norepinephrine, and epinephrine are well-known neurotransmitters playing different roles in the nervous and endocrine system. These compounds are biologically synthesized in the phenylalanine-tyrosine pathway which consists on the successive conversion of l-phenylalanine into l-tyrosine, l-3,4-dihydroxyphenylalanine (L-DOPA), dopamine, norepinephrine, and epinephrine. This work describes the development of an enantioselective CE-ESI-MS2 methodology enabling, for the first time, the simultaneous enantioseparation of all the constituents involved in the Phe-Tyr metabolic pathway, since all these compounds except dopamine are chiral. The developed method was based on the use of a dual CDs system formed by 180 mM of methyl-β-CD and 40 mM of 2-hydroxypropyl-β-CD dissolved in 2 M formic acid (pH 1.2) and presented the advantage of avoiding the use of any time-consuming labelling procedure. LODs ranged from 40 to 150 nM and the unequivocal identification of the compounds investigated was achieved through their MS2 spectra. The applicability of this methodology to the analysis of biological samples (rat plasma) was also demonstrated.