Repeller effects in discharge ionization in liquid and supercritical-fluid chromatography-mass spectrometry using a thermospray interface: II. Changes in some analyte spectra

By changing the potential of the repeller electrode in a thermospray ion source operated under discharge-on conditions in liquid chromatography mass spectrometry and supercritical-fluid chromatography-mass spectrometry the appearance of the mass spectra can be changed. Either abundant protonated molecules or considerable fragmentation can be obtained. The repeller-induced fragmentation can result in useful fragmentation. The selection of the most appropriate repeller potential is a delicate task because the effects appear to be compound-dependent. Compounds which are fragmented easily will generally not give useful spectra at very high repeller potentials. The results indicate that different mechanisms, i.e., chemical ionization with different reagent gas compositions and collisionally induced dissociation, play important roles in fragmentation.