Determination of 20 underivatized proteinic amino acids by ion-pairing chromatography and pneumatically assisted electrospray mass spectrometry

A qualitative determination of 20 underivatized proteinic amino acids by LC -MS is reported. The need for chromatographic separation before mass spectr ometry determination is demonstrated based on the study of several amino ac id pairs which have some similar characteristics. Two suitable LC-MS system s are proposed for amino acid analysis. A preliminary optimization of these systems has been investigated using evaporative light scattering detection as these two detection modes have the same chromatographic requirements. T he amino acid separation was achieved on a Purospher RP-18e or a Supelcosil ABZ(+)Plus column with tridecafluoroheptanoic acid or pentadecafluorooctan oic acid as volatile ion-pairing reagent in an acetonitrile-water mobile ph ase. In order to elute the most retained amino acids, an elution gradient b ased on simultaneously increasing the concentration of acetonitrile and dec reasing the concentration of the ion-pairing reagent was used. The detectio n limits of the present work (without specialized optimization) varied from 0.5 to 1 mg l(-1). (C) 1999 Published by Elsevier Science B.V. All rights reserved.