Mass spectrometry is a potent analytical tool to gather information regarding the chemical structure and composition of compounds. Figure shows the mass spectra for a THF solution of TCNE, an aqueous solution of melamine, and an aqueous THF solution of TCNE and melamine (TCNE-melamine) measured in the positive ion mode (panel a) and the negative ion mode (panel b). In the positive ion spectra for all samples, multiple mobile phase peaks are present. The intense peaks at m/z = 42.04 and 82.67 correspond to protonated acetonitrile [ACN + H] + (a molecular mass of 42.06 g/mol), and its dimer [2ACN + H] + (83.11 g/mol), respectively. In addition, the mass spectra for melamine and TCNE-melamine show the distinct peaks at m/z = 101.8, 126.7 and 167.6. m/z = 126.92 corresponds to the [Melamine + H] + ion (a molecular mass of 127.13 g/mol) . The peak at m/z = 167.6 can be attributed to an adduct of melamine and acetonitrile [Melamine + ACN + H] + (168.18 g/mol) . The chemical structure corresponding to m/z = 101.8 could be a decomposed product of melamine.