A fast and sensitive capillary liquid chromatography (cLC) column-switching method with electrospray ionization time-of-flight mass spectrometry (ESI–TOF–MS) detection for the simultaneous determination of dopamine (D), epinephrine (E), norepinephrine (NE) and serotonin (SE) was pursued. A sample volume of 100μl was loaded with a mobile phase containing 0.1% pentafluoropropionic acid (PFPA) as ion-pairing agent on a 25mm×0.32mm (i.d.) 5μm Hypercarb column. A water–acetonitrile (AcN) gradient with 0.1% acetic acid (AcOH) backflushed the compounds onto a 34mm×0.32mm (i.d.) 5μm Hypercarb analytical column. However, during a series of analyses, oxidation of the catecholamines (CAs) was observed. This was suspected to be due to the loading mobile phase composition and precluded the usefulness of this method even though the achievable detection limit was in the range of 0.75–3.0ng/ml. The combination of the porous graphitic carbon (PGC) material and the fluorinated strong acids which were required to get enough retention for preconcentration of large volumes cannot be used for easily oxidized compounds as the CAs.