Field‐dependent [M – 2H]+. formation in the field desorption mass spectrometric analysis of hydrocarbon samples

High‐boiling hydrocarbons often yield abundant [M — 2H]+. ions under the conditions of field desorption mass spectrometry (FDMS). This work evaluated [M — 2H]+. formation from various saturated and aromatic compounds. The most intense [M — 2H]+. signals observed resulted from the analysis of saturated compounds containing long and branched chains. The presence of an aromatic ring in a molecule, however, strongly diminished [M — 2H]+. formation during FDMS. Experiments involving manipulation of the applied potential between the FD anode and cathode reveal the strong field dependence of this phenomenon. At a potential difference of 10 kV, strong [M — 2H]+. formation occurred for samples including squalane, hexatriacontane (C36 n‐alkane) and a Polywax 655 mixture. Analyses of the same samples conducted at a potential difference of 4 kV produced only weak (if measurable) [M — 2H+.] signals. The magnitude of [M — 2H]+. formation also decreased as the sample quantity decreased.