Elucidation of phosphatidylcholine isomers using two dimensional liquid chromatography coupled in-line with ozonolysis mass spectrometry

Positional Assignment of C-C Double Bonds in Fatty Acyl Chains of Intact Arsenosugar Phospholipids Occurring in Seaweed Extracts by Epoxidation Reactions

Water-soluble diacyl arsenosugar phospholipids (As-PL) are natural products widespread in marine animals and algae, including the brown alga Undaria pinnatifida, also known as wakame. The systematic recognition of As-PL has been hampered by the lack of standard and of qualitative methods to establish the carbon-carbon double bond positions of unsaturated fatty acyl chains. Here, the epoxidation reaction of fatty acyl substituents of As-PL was carried out with high selectivity by meta-chloroperoxybenzoic acid and the C-C double bond localization was established by collision-induced dissociation of epoxidized species as deprotonated molecules, [epoM - H]-. Reversed-phase liquid chromatography (RPLC) separation and a sequential triple-stage MS (i.e., MS3) analysis of unsaturated and epoxidized As-PL were very helpful to characterize the carbon-carbon double bond locations of both sn-1 and sn-2 fatty acyl chains, starting from a diagnostic product ion pair with 16.0 Da mass difference. These results indicate that intact As-PL can be annotated in terms of fatty acyl chain composition and in terms of their C-C double bond position(s). Interestingly, hexadecenoic (16:1 Δ9) and octadecenoic (18:1 Δ9) along with octadecadienoic (18:2 Δ9,12) and octadecatrienoic (18:3 Δ9,12,15) were found to be the most abundant unsaturated fatty acyl chains of As-PL in the brown alga wakame, thus confirming it as a good source of essential fatty acids with a balanced ω6/ω3 ratio. Although the toxicity of As-including metabolites of algal As-PL is still a matter of debate and needs to be studied in more detail, the described approach can be exploited to assess if As-PL could contribute to the supply of essential fatty acids related to the use of algae as nutritious food.

Fundamentals of Ion Mobility-Mass Spectrometry for the Analysis of Biomolecules

Ion mobility-mass spectrometry (IM-MS) combines complementary size- and mass-selective separations into a single analytical platform. This chapter provides context for both the instrumental arrangements and key application areas that are commonly encountered in bioanalytical settings. New advances in these high-throughput strategies are described with description of complementary informatics tools to effectively utilize these data-intensive measurements. Rapid separations such as these are especially important in systems, synthetic, and chemical biology in which many small molecules are transient and correspond to various biological classes for integrated omics measurements. This chapter highlights the fundamentals of IM-MS and its applications toward biomolecular separations and discusses methods currently being used in the fields of proteomics, lipidomics, and metabolomics.

Comparison of the Fatty Acid and Triglyceride Profiles of Big Eye Tuna (Thunnus obesus), Atlantic salmon (Salmo salar) and Bighead Carp (Aristichthysnobilis) Heads

Big eye tuna (Thunnus obesus), Atlantic salmon (Salmo salar) and bighead carp (Aristichthys nobilis) are three representative marine and fresh water fishes. In this study, the content of total lipids (TL), triglyceride (TG) fraction, and the fatty acid profiles in the corresponding fish heads were analyzed. Meanwhile, their complicated TG molecular species were further characterized. The results showed that TG was the major lipid in these three fish heads (60.58–86.69%). Compared with other two fish heads, big eye tuna head was the most abundant in polyunsaturated fatty acids, among which eicosapentaenoic acid (EPA) + docosahexaenoic acid (DHA) accounted for 64.29% and 32.77% in the TL and TG fraction, respectively. It is also worth noting that EPA+DHA/total fatty acid (TFA) value of TL and TG fraction from bighead carp head showed no significant difference with Atlantic salmon head, a typical marine fish. There were 146 TG molecules detected in big eye tuna head, 90 in Atlantic salmon and 87 in bighead carp heads. DHA or EPA accounted for 56.12%, 22.88%, and 5.46% of the total TG molecules in these three fish heads, respectively. According to principal component analysis, orthogonal projection to latent structures-discriminant analysis and the constructed heat map, the three samples could be completely differentiated based on their TG molecule fingerprints. This study is the first to compare marine and fresh water fish from the perspective of their heads’ fatty acid and TG molecule profiles.

Carbon-carbon double bond position elucidation in fatty acids using ozone-coupled direct analysis in real time mass spectrometry

The carbon-carbon double bond positions of unsaturated fatty acids can have markedly different effects on biological function and also serve as biomarkers of disease pathology, dietary history, and species identity. As such, there is great interest in developing methods for the facile determination of double bond position for natural product chemistry, the pharmaceutical industry, and forensics. We paired ozonolysis with direct analysis in real time mass spectrometry (DART MS) to cleave and rapidly identify carbon-carbon double bond position in fatty acids, fatty alcohols, wax esters, and crude fatty acid extracts. In addition, ozone exposure time and DART ion source temperature were investigated to identify optimal conditions. Our results reveal that brief, offline exposure to ozone-generated aldehyde and carboxylate products that are indicative of carbon-carbon double bond position. The relative abundance of diagnostic fragments quantitatively reflects the ratios of isobaric fatty acid positional isomers in a mixture with a correlation coefficient of 0.99. Lastly, the unsaturation profile generated from unfractionated, fatty acid extracts can be used to differentiate insect species and populations. The ability to rapidly elucidate lipid double bond position by combining ozonolysis with DART MS will be useful for lipid structural elucidation, assessing isobaric purity, and potentially distinguishing between animals fed on different diets or belonging to different ecological populations.

UV Lamp as a Facile Ozone Source for Structural Analysis of Unsaturated Lipids Via Electrospray Ionization-Mass Spectrometry

Ozonolysis of alkene functional groups is a type of highly specific and effective chemical reaction, which has found increasing applications in structural analysis of unsaturated lipids via coupling with mass spectrometry (MS). In this work, we utilized a low-pressure mercury lamp (6 W) to initiate ozonolysis inside electrospray ionization (ESI) sources. By placing the lamp near a nanoESI emitter that partially transmits 185 nm ultraviolet (UV) emission from the lamp, dissolved dioxygen in the spray solution was converted into ozone, which subsequently cleaved the double bonds within fatty acyls of lipids. Solvent conditions, such as presence of water and acid solution pH, were found to be critical in optimizing ozonolysis yields. Fast (on seconds time scale) and efficient (50%-100% yield) ozonolysis was achieved for model unsaturated phospholipids and fatty acids with UV lamp-induced ozonolysis incorporated on a static and an infusion nanoESI source. The method was able to differentiate double bond location isomers and identify the geometry of the double bond based on yield. The analytical utility of UV lamp-induced ozonolysis was further demonstrated by implementation on a liquid chromatography (LC)-MS platform. Ozonolysis was effected in a flow microreactor that was made from ozone permeable tubing, so that ambient ozone produced by the lamp irradiation could diffuse into the reactor and induce online ozonolysis post-LC separation and before ESI-MS. Graphical Abstract ᅟ.

Optimizing separations in online comprehensive two-dimensional liquid chromatography

Online comprehensive two-dimensional liquid chromatography has become an attractive option for the analysis of complex nonvolatile samples found in various fields (e.g. environmental studies, food, life, and polymer sciences). Two-dimensional liquid chromatography complements the highly popular hyphenated systems that combine liquid chromatography with mass spectrometry. Two-dimensional liquid chromatography is also applied to the analysis of samples that are not compatible with mass spectrometry (e.g. high-molecular-weight polymers), providing important information on the distribution of the sample components along chemical dimensions (molecular weight, charge, lipophilicity, stereochemistry, etc.). Also, in comparison with conventional one-dimensional liquid chromatography, two-dimensional liquid chromatography provides a greater separation power (peak capacity). Because of the additional selectivity and higher peak capacity, the combination of two-dimensional liquid chromatography with mass spectrometry allows for simpler mixtures of compounds to be introduced in the ion source at any given time, improving quantitative analysis by reducing matrix effects. In this review, we summarize the rationale and principles of two-dimensional liquid chromatography experiments, describe advantages and disadvantages of combining different selectivities and discuss strategies to improve the quality of two-dimensional liquid chromatography separations.

A method of coupling the Paternò–Büchi reaction with direct infusion ESI-MS/MS for locating the CC bond in glycerophospholipids

Conducting the Paternò–Büchi reaction in a microflow photo-reactor enables its coupling with ESI-MS/MS and CC location determination for shotgun lipid analysis.

Recent advances in 2D-LC for bioanalysis

This article summarizes the most important developments in the use of 2D-LC for bioanalysis in the last 5 years. While several interesting and powerful applications have been developed recently, this work has been supported by continued, significant development of theoretical concepts, instrument development and practical aspects of method development. Some of the most exciting applications have been focused on the use of 2D-LC and characterize proteins both as biotherapeutic drug substances, and in formulations. These materials are inherently complex, difficult to resolve chromatographically and present problems that are essentially unknown (e.g., aggregation) in the small molecule world, thus 2D-LC can be leveraged very effectively to address these challenges.

Characterization of phospholipids by two-dimensional liquid chromatography coupled to in-line ozonolysis-mass spectrometry

In this study, the characterization of phospholipids (PL) was achieved by using a combination of LC/MS/MS and two-dimensional LC/MS. A HILIC LC column was used for PL class separation, while the further molecular species separation of each PL class was achieved by using online HILIC × C18 LC. The double bond positions along the fatty acyl chains of these PL molecular species were also obtained by using the combination of 2D-LC and in-line ozonolysis-MS analysis. The ozonolysis device is composed of a gas-permeable, liquid-impermeable Teflon tube passing through a glass chamber filled with ozone gas, which is then placed in-line between the 2D-LC and the mass spectrometer. The eluting PL molecules in the LC mobile phase passed through the device where they rapidly reacted with the ozone that penetrated through the tubing wall. The ozonolysis products were then detected by MS in real-time, which allowed the localization of the double bonds along the fatty acyl chains in these PL molecular species. This comprehensive method was successfully applied to an egg yolk PL extract, which revealed the detailed structures of the PL molecules.