Optimized precursor ion selection for labile ions in a linear ion trap mass spectrometer and its impact on quantification using selected reaction monitoring

Evaluation of Lipid In-Source Fragmentation on Different Orbitrap-based Mass Spectrometers

Natural lipidomes represent a complex mixture of lipid molecular species with a variety of biological and signaling functions. Modern mass spectrometry (MS)-based analytical platforms are often used to resolve the complexity of natural lipidomes. The quantitative transfer of lipid molecular species in the gas phase during the electrospray ionization required for MS analysis might be challenged by lipid in-source fragmentation (ISF) hampering their accurate identification and quantification. Here we evaluated the effect of transmission radio frequency (RF) levels and ion transfer temperatures (ITTs) on the analysis of four different lipids (ceramide, cholesteryl ester, phosphatidylethanolamine, and triacylglyceride) ionized in positive ion mode on three different Orbitrap-based platforms. ITT and RF levels were ramped in a systematic way to determine the best settings, allowing the most sensitive detection accompanied by the lowest ISF of a lipid. The extent of the ISF was shown to depend on the configurations of the transmission devices (S-lens vs letterbox/ion funnel) at defined RF and ITT levels for each studied lipid class. We provide here the recommendations for reducing the extent of lipid ISF without a significant loss in sensitivity for Q Exactive HF, Q Exactive HF-X, and Orbitrap Fusion Lumos platforms.

Multiple stage MS in analysis of plasma, serum, urine and in vitro samples relevant to clinical and forensic toxicology

This paper reviews MS approaches applied to metabolism studies, structure elucidation and qualitative or quantitative screening of drugs (of abuse) and/or their metabolites. Applications in clinical and forensic toxicology were included using blood plasma or serum, urine, in vitro samples, liquids, solids or plant material. Techniques covered are liquid chromatography coupled to low-resolution and high-resolution multiple stage mass analyzers. Only PubMed listed studies published in English between January 2008 and January 2015 were considered. Approaches are discussed focusing on sample preparation and mass spectral settings. Comments on advantages and limitations of these techniques complete the review.