Liquid chromatography-dielectric barrier discharge ionization mass spectrometry for the analysis of neutral lipids of archaeological interest

Dielectric barrier discharge ionization has gained attention in the last few years due to its versatility and the vast array of molecules that can be ionized. In this study, we report on the assessment of liquid chromatography coupled to dielectric barrier discharge ionization with mass spectrometry for neutral lipid analysis. A set of different neutral lipid subclasses (triacylglycerides, diacylglycerides, and sterols) were selected for the study. The main species detected from our ionization source were [M-H2O+H](+), [M+H](+) or [M-R-H2O+H](+), attributed to sterol dehydration, protonation or the fragmentation of an acyl chain accompanied by a water loss of the glycerolipids, respectively. In terms of sensitivity, the dielectric barrier discharge displayed overall improved abundances and comparable or better limits of quantitation than atmospheric pressure chemical ionization for both acylglycerols and sterols. As a case study, different archaeological samples with variable content in neutral lipids, particularly triacylglycerides, were studied. The identification was carried out by combining accurate mass and the tentative formula associated with the exact mass, retention time matching with standards, and additional structural information from in-source fragmentation. The high degree of unsaturation and the presence of sterols revealed the potential vegetal origin of the material stored in the analyzed samples.