Reactive Thread Spray Mass Spectrometry for Localization of C═C Bonds in Free Fatty Acids: Applications for Obesity Diagnosis

Abstract

Cellulose thread substrates offer a platform for microsampling and reactive ionization of free fatty acid (FFA) isomers for direct differentiation by mass spectrometry. Ambient corona discharge forms when direct current high voltage is applied to the tiny subfibers on the thread substrate in the presence of a polar spray solvent (MeOH/H2O, 2:1, v/v), facilitating chemical reactions across a CC bond of unsaturated fatty acids. The process was applied for diagnosis of obesity, which we observed to show better discriminatory power when compared to determinations based on body mass index. Overall, the integrated reactive thread-based platform is capable of (i) microsampling and dry-state, room-temperature storage (>30 days) of the biofluids, (ii) in-capillary liquid/liquid extraction, and (iii) in situ epoxidation reactions to locate the CC bond position in unsaturated fatty acids via reactions with reactive oxygen species present in ambient corona discharge. The study showcased the ability to correctly characterize FFAs, including degree of unsaturation, and the determination of their relative concentrations in clinical biofluid samples.

Deep-lipidotyping by mass spectrometry: recent technical advances and applications

“…Very recently, peracetic acid was used as the epoxidation reagent and it was applied for mapping C=C location isomers of FAs in tissues via MALDI-MS/MS ( 63 ). Other epoxidation strategies have also been explored; for example, Oxone was used as the epoxidation reagent and applied for the analysis of FA C=C isomers in human plasma samples ( 78 ); epoxidation of unsaturated FAs was achieved by pulsed corona discharge generated by triboelectric nanogenerators ( 79 ) and by atmospheric pressure chemical ionization ( 80 ).…”

Plasma-Droplet Reaction Systems: A Direct Mass Spectrometry Approach for Enhanced Characterization of Lipids at Multiple Isomer Levels

“…It is important to consider the hydrolysis of TGs to give substituent FAs as this is one process responsible for the total FA expression in a biological system. As demonstrated by others, FA expression, including the degree of unsaturation and position of CC bonds, can give insight into the metabolic health of individuals and have implications in obesity, diabetes, and heart disease . Thus, after demonstrating the use of the coaxial contained platform with etched silica capillaries for plasma-droplet fusing reactions of TGs for CC positional analysis, we aimed to evaluate the emitter’s capacity to perform isomeric mixture analysis of FAs.…”

“…For free fatty acids, the distinct fragmentation of the epoxide ring has been widely discussed (Scheme S1), which is known to give two diagnostic ions that are 16 Da apart signaling the specific location of a C�C bond along the carbon chain. 48,57 We have observed a novel fragmentation pattern for epoxides derived from TG lipids. Scheme 2 provides a cartoon depiction of the MS/MS process for generating quadruplet diagnostic ions for a TG with a single double bond (Scheme 2A) and TG with two double bonds (Scheme 2B) along the acyl chains.…”

“…As demonstrated by others, FA expression, including the degree of unsaturation and position of C�C bonds, can give insight into the metabolic health of individuals and have implications in obesity, diabetes, and heart disease. 48 Thus, after demonstrating the use of the coaxial contained platform with etched silica capillaries for plasma-droplet fusing reactions of TGs for C�C positional analysis, we aimed to evaluate the emitter's capacity to perform isomeric mixture analysis of FAs. We perform FA analysis of the complex EVOO sample to determine if some of the exotic side chains identified (e.g., 18:2(10,12)) can be confirmed as FA released are a hydrolytic product from TGs.…”

“…The OzESI process produces complex spectra because diagnostic ions appear with molecular ions in full MS (without mass selection) making spectral interpretation difficult . Epoxidation of the CC bond for characterization of double-bond configuration has gained interest recently and has been performed offline via bulk phase meta-chloroperoxybenzoic acid (m-CPBA) epoxidation and via the use of reactive oxygen species (ROS) produced in nonthermal plasma discharge. − Epoxidation via ROS in nonthermal plasma is of interest because the reaction proceeds faston the timescale of MS acquisition, occurs under atmospheric conditions with no added reagents, and produces well-defined, characteristic fragment ions upon subjecting the epoxide ring to CID.…”