Evolution of DART and Ambient Ionization for the Analysis of Oils and Surfactants

Abstract: Direct Analysis in Real Time (DART) mass spectrometry was introduced to AOCS through a February 2008 cover story in INFORM. Ambient ionization was a relatively new concept, with the commercial introduction of the DART ion source only three years prior. The methodology and applications have evolved considerably in the past 17 years, with a broader range of applications, including biodiesel feedstocks, sea turtle oil, cosmetics, and cooking oils. Chemometric methods combined with DART make it possible to distinguish oils from different sources and identify adulterated products. Variations on the DART ionization mechanism facilitate the identification of various compound classes. For example, argon DART with chlorobenzene dopant makes it easy to selectively identify conjugated lipids such as carotenoids in complex mixtures. Negative-ion DART provides selective detection of phenolic compounds in olive oils. Oxygen adduct formation in negative-ion DART selectively ionizes large alkanes and alcohols. Polar compounds such as ionic surfactants that are not ionized by DART can easily and rapidly be detected with alternative open-air mass spectrometry techniques, such as PaperSpray. Speed and ease of use make ambient ionization mass spectrometry a convenient method to obtain an overview of the chemical composition of lipid-based products to complement the information from other mass spectrometric methods such as GC-MS and MALDI-MS.