Mass spectrometry of biogenic catecholamine ion pairs by direct liquid introduction

The mass spectrometry of ion pairs of dopamine, noradrenaline and 3,4-dihydroxyphenylacetic acid with n-octylsulphonate has been investigated by direct liquid introduction in an acidic buffer currently used for their high-performance liquid chromatographic separation. In order to follow the fate of the ion pairs, they were first studied by desorption/chemical ionization as dichloromethane extracts or in the buffer. The results show that characteristic spectra of the solutes can be obtained by direct liquid introduction provided that the interface between the chromatographic system and the mass spectrometer permits the desolvation of the ion pairs from the cluster of solvent molecules.