Some compounds, including saturated alkanes and alcohols do not readily undergo proton transfer reactions. These compounds can be analyzed with the DART ion source by forming adducts with oxygen anions. For this experiment, samples in solution are aspirated directly into the sampling orifice of the AccuTOF atmospheric pressure interface while the DART is operated in negative-ion mode as a source of O2. Rapid expansion into vacuum cools the weakly bound [M + O2] ─• species for detection by the AccuTOF.
Negative-ion O2─• attachment DART mass spectrum of motor oil, showing the base oil components including C24-C44 alkanes and an alkylnapthalene.