Abstract
The practical limitations of miniaturized liquid chromatography (LC) methods for the analysis of endogenous peptides in plasma samples are studied. An automatic column switching method is used for on‐line micropreconcentration and microLC‐MS–MS (mass spectrometry) analysis of bradykinin and its metabolites in plasma. Both preconcentration (PC) and analytical columns were filled with C18 reversed phase due to the failure of anion exchange precolumns to retain bradykinins. The detection limit for bradykinin in water was 10 pmol/L (2 fmols on column) and a good linearity was found in the range 5–2000 fmols. In plasma, detection limit was 50 pmol/L (25 μL injected) with a linear response in the 100–2000 pmol/L range. Important rules for stable work were: (1) Cleaning the PC column after every run with pure acetonitrile (ACN) to eliminate organic matrix components; (2) to trap the more apolar organic matrix components on the analytical column to prevent their elution to the MS entrance; and (3) to set the electrospray needle to an off‐axis position to prevent accumulation of contaminants in the MS entrance. By using this setup, other procedures to reduce the organic load to the MS entrance such as the heart‐cutting of the peaks eluting from the LC column were not required. © 2001 John Wiley & Sons, Inc. J Micro Sep 13: 265–274, 2001