The mass spectrometric properties of several (1,2-dimethyl-1H-imidazol-3-ium-3-yl)-alkane-1-sulfonates (alkane=ethyl, propyl and butyl) are investigated in this study. These substances, named zwitterionic liquids (ZILs), were synthesized using classical transformations and analyzed in positive and negative electrospray ionization mode using collision-induced dissociation (0-50 eV). We have also performed regioselective deuterium labeling of the alkyl chain of 3-(1,2-dimethyl-1H-imidazol-3-ium-3-yl)-propane-1-sulfonates. Thus, the mass spectra of isotopically-labeled compounds were used for the confirmation of fragmentation pathways of ZILs. Briefly, the data obtained in this study show that the fragmentation of ZILs is dependent on the alkyl chain length between the imidazolium ring and the sulfonate group. In positive electrospray mode, the main fragments are the imidazolium ring containing even electron ions. On the other hand, in negative electrospray mode, sulfur-containing radical-anions are dominant.