Structural characterization of bacterial lipopolysaccharides with mass spectrometry and on‐ and off‐line separation techniques

The focus of this review is the application of mass spectrometry to the structural characterization of bacterial lipopolysaccharides (LPSs), also referred to as “endotoxins,” because they elicit the strong immune response in infected organisms. Recently, a wide variety of MS‐based applications have been implemented to the structure elucidation of LPS. Methodological improvements, as well as on‐ and off‐line separation procedures, proved the versatility of mass spectrometry to study complex LPS mixtures. Special attention is given in the review to the tandem mass spectrometric methods and protocols for the analyses of lipid A, the endotoxic principle of LPS. We compare and evaluate the different ionization techniques (MALDI, ESI) in view of their use in intact R‐ and S‐type LPS and lipid A studies. Methods for sample preparation of LPS prior to mass spectrometric analysis are also described. The direct identification of intrinsic heterogeneities of most intact LPS and lipid A preparations is a particular challenge, for which separation techniques (e.g., TLC, slab‐PAGE, CE, GC, HPLC) combined with mass spectrometry are often necessary. A brief summary of these combined methodologies to profile LPS molecular species is provided. © 2012 Wiley Periodicals, Inc., Mass Spec Rev 32:90–117, 2013     

A method for the identification and quantitation of hydraulic fluid contamination of turbine engine oils by gas chromatography–chemical ionisation mass spectrometry

The identification of aircraft hydraulic fluid contamination of turbine engine oils is difficult. Repeated field incidents of this type of cross contamination have led to the requirement to develop a method suitable for quantitation of such contamination. A gas chromatography–chemical ionisation mass spectrometry method for the determination of H‐537 hydraulic fluid contamination in turbine engine oil was developed and validated. The intraday and interday relative standard deviations of the standards were 3–7% and 5–9%, respectively. Mean recoveries of hydraulic fluid in turbine engine oil were 90–94%, and the calibration curve was linear with R² = 0.999. Limits of detection and quantitation were 0.05% (w/w) and 0.5% (w/w), respectively. The method was successfully applied to laboratory degraded samples and field samples. Copyright © 2012 John Wiley & Sons, Ltd.     

Top‐down mass spectrometry for the analysis of combinatorial post‐translational modifications

Protein post‐translational modifications (PTMs) are critically important in regulating both protein structure and function, often in a rapid and reversible manner. Due to its sensitivity and vast applicability, mass spectrometry (MS) has become the technique of choice for analyzing PTMs. Whilst the “bottom‐up' analytical approach, in which proteins are proteolyzed generating peptides for analysis by MS, is routinely applied and offers some advantages in terms of ease of analysis and lower limit of detection, “top‐down” MS, describing the analysis of intact proteins, yields unique and highly valuable information on the connectivity and therefore combinatorial effect of multiple PTMs in the same polypeptide chain. In this review, the state of the art in top‐down MS will be discussed, covering the main instrumental platforms and ion activation techniques. Moreover, the way that this approach can be used to gain insights on the combinatorial effect of multiple post‐translational modifications and how this information can assist in studying physiologically relevant systems at the molecular level will also be addressed. © 2012 Wiley Periodicals, Inc., Mass Spec Rev 32:27–42, 2013     

Recent developments of proton‐transfer reaction mass spectrometry (PTR‐MS) and its applications in medical research

Proton‐transfer reaction mass spectrometry (PTR‐MS) allows for real‐time, on‐line determination of absolute concentrations of volatile organic compounds (VOCs) with a high sensitivity and low detection limits (in the pptv range). The technique utilizes H₃O⁺ ions for proton‐transfer reactions with many common VOCs while having little to no reaction with any constituents commonly present in air. Over the past decades, research has greatly improved the applications and instrumental design of PTR‐MS. In this article, we give an overview of the development of PTR‐MS in recent years and its application in medical research. The theory of PTR‐MS and various methods for discriminating isobaric VOCs are also described. We also show several specialized designs of sample inlet system, some of those may make PTR‐MS suitable for the detection of aqueous solution and/or non‐volatile samples. © 2012 Wiley Periodicals, Inc., Mass Spec Rev 32:143–165, 2013     

Advances on the compositional analysis of glycosphingolipids combining thin‐layer chromatography with mass spectrometry

Glycosphingolipids (GSLs), composed of a hydrophilic carbohydrate chain and a lipophilic ceramide anchor, play pivotal roles in countless biological processes, including infectious diseases and the development of cancer. Knowledge of the number and sequence of monosaccharides and their anomeric configuration and linkage type, which make up the principal items of the glyco code of biologically active carbohydrate chains, is essential for exploring the function of GSLs. As part of the investigation of the vertebrate glycome, GSL analysis is undergoing rapid expansion owing to the application of novel biochemical and biophysical technologies. Mass spectrometry (MS) takes part in the network of collaborations to further unravel structural and functional aspects within the fascinating world of GSLs with the ultimate aim to better define their role in human health and disease. However, a single‐method analytical MS technique without supporting tools is limited yielding only partial structural information. Because of its superior resolving power, robustness, and easy handling, high‐performance thin‐layer chromatography (TLC) is widely used as an invaluable tool in GSL analysis. The intention of this review is to give an insight into current advances obtained by coupling supplementary techniques such as TLC and mass spectrometry. A retrospective view of the development of this concept and the recent improvements by merging (1) TLC separation of GSLs, (2) their detection with oligosaccharide‐specific proteins, and (3) in situ MS analysis of protein‐detected GSLs directly on the TLC plate, are provided. The procedure works on a nanogram scale and was successfully applied to the identification of cancer‐associated GSLs in several types of human tumors. The combination of these two supplementary techniques opens new doors by delivering specific structural information of trace quantities of GSLs with only limited investment in sample preparation. © 2009 Wiley Periodicals, Inc. Mass Spec Rev 29:425‐479, 2010     

Effect of the chemical structure of fluorinated esters on the tribological properties of a steel‐on‐steel system

The effect of the chemical structure of fluorinated esters on the friction and wear behaviour of a steel‐on‐steel system was investigated. The friction and wear testing of a steel disc sliding against a counterpart ball of the same steel was carried out using an Optimal SRV oscillating friction and wear tester. The chemical features of the worn steel surfaces were analysed by means of X‐ray photoelectron spectroscopy, and the morphologies and elemental compositions of the worn steel surfaces observed and determined using scanning electron microscopy. The results indicate that a fluorinated ester with methylene groups that are not substituted by fluorine in the acid structure gives the best friction‐reducing behaviour and a keto‐ester shows the best antiwear properties.     

FTIR micro‐reflectance absorption spectroscopic analysis of chemisorbed reaction films for tribological applications

Chemisorbed reaction films (CRFs) were prepared by using iron (Fe) particles (100–200 mess size) and thio (sulfur) derivatives of ethyl octadecenoate and methyl 12‐hydroxy octadecenoate in the light viscosity paraffin liquid medium. The reaction was conducted in a simulated condition of tribo‐chemical situation. CRFs were obtained in solid amorphous phase. The CRFs were examined for elemental composition and layer analysis using C‐H‐N‐O‐S analyzer and Fourier transform infrared spectroscopy micro‐reflectance absorption spectroscopic technique. Further, the CRFs were isolated into organic solvent soluble fractions using polar solvents of increasing polar strength. Their elemental analyses were studied, and chemical constitutions were known. Friction coefficient and wear scar diameter were evaluated by high frequency reciprocating rig, PLINT TE‐77 machine. Thermal stability was studied using thermogravimetric analysis technique in nitrogen environment. These studies inferred that CRFs appeared varying in its composition, luster, phase, chemical structure and thermal stability. Nonetheless, these were also found anomalous in elemental distribution throughout the layer structure of the CRFs. Copyright © 2015 John Wiley & Sons, Ltd.     

Determination of polychlorinated dibenzo-p-dioxins,dibenzofurans, and biphenyls by gas chromatography/mass spectrometry in the negative chemical ionization mode with different reagent gases

Reagent gases that are used in mass spectrometry in the NCI mode for the determination of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), and biphenyls (PCBs) are discussed. Ion-molecule reactions and respective characteristic ions that form while using reagent gases (CH(4), O(2), i-C(4)H(10), NH(3), H(2), He, Ar, Xe, SF(6)) or gas mixtures (CH(4)/O(2), Ar/CH(4), CH(4)/H(2)O, Ar/O(2), i-C(4)H(10)/CH(2)Cl(2)/O(2)) are reviewed. It is shown that only CH(4), O(2), CH(4)/O(2), and CH(4)/N(2)O are widely used and well studied, even though-in the case of these reagent gases-there are contradictions between the publications of various authors. Such reagent gases as NH(3) and He are not well studied, but further investigations of their use for the determination of organochlorine pollutants could be of interest. The possibilities of more sensitive and selective determination of PCDDs, PCDFs, and PCBs are discussed.     

Analysis of carbohydrates and glycoconjugates by matrix‐assisted laser desorption/ionization mass spectrometry: An update for the period 2005–2006

This review is the fourth update of the original review, published in 1999, on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2006. The review covers fundamental studies, fragmentation of carbohydrate ions, method developments, and applications of the technique to the analysis of different types of carbohydrate. Specific compound classes that are covered include carbohydrate polymers from plants, N‐ and O‐linked glycans from glycoproteins, glycated proteins, glycolipids from bacteria, glycosides, and various other natural products. There is a short section on the use of MALDI‐TOF mass spectrometry for the study of enzymes involved in glycan processing, a section on industrial processes, particularly the development of biopharmaceuticals and a section on the use of MALDI–MS to monitor products of chemical synthesis of carbohydrates. Large carbohydrate–protein complexes and glycodendrimers are highlighted in this final section. © 2010 Wiley Periodicals, Inc., Mass Spec Rev 30:1–100, 2011