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[2]. 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.