Soft Ionization Mass Spectrometry Research Articles

Soft ionisation analysis of evolved gas for oxidative decomposition of an epoxy resin/carbon fibre composite

Soft ionisation mass spectrometry was used to investigate the oxidative decomposition of an epoxy resin/carbon fibre composite using thermogravimetry (TG) coupled with mass spectrometry (MS). Through comparison between decomposition in air and in argon, it was recognized that the first step of the oxidative decomposition of the epoxy resins was similar to the decomposition in argon. During the devolatilisation process, the oxidative decomposition underwent a thermal decomposition leading to the formation of a large amount of volatile products which were subsequently oxidized into water and carbon dioxide. The gas produced in the thermal decomposition was not oxidized completely leaving some organic volatiles in the emissions. Using soft ionisation, the components of the evolved gases were identified by mass spectrometry.

Critical evaluation of mass spectrometric measurement of dissociation constants: accuracy and cross-validation against surface plasmon resonance and circular dichroism for the calmodulin–melittin system

We present a comprehensive study for determining the binding affinity of a protein-ligand complex, using mass spectrometric methods. Mass spectrometry has been used to study noncovalent interactions for a number of years. However, the use of soft ionization mass spectrometry for quantitative analysis of noncovalently bound complexes is not widely accepted. This paper reports a comparison of MS methods against established methods such as surface plasmon resonance (SPR) and circular dichroism (CD) whose suitability for the quantitative assessment of noncovalent interactions is well known. ESI titration and MALDI-SUPREX were used as representative mass spectrometric methods for this work. We chose to study the calmodulin-melittin complex that presents three challenges: (i) it exhibits a high affinity (low nanomolar KD); (ii) complexes are formed only in the presence of a coactivator, calcium ions in this case; and (iii) the protein and the complex show a different ionization efficiency. Dissociation constants were obtained from each method for the selected system and compared thoroughly to elucidate pros and cons of the selected methodologies in terms of their ability for the determination of binding constants of protein-ligand complexes. ESI titration, SPR, CD and MALDI-SUPREX yielded KD values in the low nanomolar range that are in general agreement with an older value reported in the literature. We also critically evaluated the limitations in particular of the MS methods and the associated data evaluation procedures. We present an improved evaluation of SUPREX data, as well as a detailed error analysis for all methods used.

Reaction of Primary and Secondary Amines to Form Carbamic Acid Glucuronides

Glucuronidation is an important mechanism used by mammalian systems to clear and eliminate both endogenous and foreign chemicals. Many functional groups are susceptible to conjugation with glucuronic acid, including hydroxyls, phenols, carboxyls, activated carbons, thiols, amines, and selenium. Primary and secondary amines can also react with carbon dioxide (CO(2)) via a reversible reaction to form a carbamic acid. The carbamic acid is also a substrate for glucuronidation and results in a stable carbamate glucuronide metabolite. The detection and characterization of these products has been facilitated greatly by the advent of soft ionization mass spectrometry techniques and high field NMR instrumentation. The formation of carbamate glucuronide metabolites has been described for numerous pharmaceuticals and they have been identified in all of the species commonly used in drug metabolism studies (rat, dog, mouse, rabbit, guinea pig, and human). There has been no obvious species specificity for their formation and no preference for 1 degrees or 2 degrees amines. Many biological reactions have also been described in the literature that involve the reaction of CO(2) with amino groups of biomolecules. For example, CO(2) generated from cellular respiration is expired in part through the reversible formation of a carbamate between CO(2) and the alpha-amino groups of the alpha- and beta-chains of hemoglobin. Also, carbamic acid products of several amines, such as beta-N-methylamino-L-alanine (BMAA), ethylenediamine, and L-cysteine have been implicated in toxicity. Studies suggested that a significant portion of amino-compounds in biological samples (that naturally contain CO(2)/bicarbonate) can be present as a carbamic acid.

Thematic review series: Systems Biology Approaches to Metabolic and Cardiovascular Disorders. Lipidomics: a global approach to lipid analysis in biological systems

Lipids are water-insoluble molecules that have a wide variety of functions within cells, including: 1) maintenance of electrochemical gradients; 2) subcellular partitioning; 3) first- and second-messenger cell signaling; 4) energy storage; and 5) protein trafficking and membrane anchoring. The physiological importance of lipids is illustrated by the numerous diseases to which lipid abnormalities contribute, including atherosclerosis, diabetes, obesity, and Alzheimer's disease. Lipidomics, a branch of metabolomics, is a systems-based study of all lipids, the molecules with which they interact, and their function within the cell. Recent advances in soft-ionization mass spectrometry, combined with established separation techniques, have allowed the rapid and sensitive detection of a variety of lipid species with minimal sample preparation. A "lipid profile" from a crude lipid extract is a mass spectrum of the composition and abundance of the lipids it contains, which can be used to monitor changes over time and in response to particular stimuli. Lipidomics, integrated with genomics, proteomics, and metabolomics, will contribute toward understanding how lipids function in a biological system and will provide a powerful tool for elucidating the mechanism of lipid-based disease, for biomarker screening, and for monitoring pharmacologic therapy.

Gas‐Phase Spectroscopy of the Unstable Sulfur Diisocyanate Molecule S(NCO)2

Sulfur diisocyanate is generated from a heterogeneous reaction of gaseous sulfur dichloride with silver cyanate and studied for the first time in the gas phase. Combined with quantum chemical calculations, the electronic structure is characterized by photoelectron spectroscopy (PES). Simultaneously, an investigation of the possible ionization and dissociation processes for the molecular cation is presented based on experimental soft ionization mass spectrometry. From the calculated bond-dissociation energies, the dissociation pathway is determined. S(NCO)2+ undergoes 1,3-sigmatropic rearrangement with a smaller barrier height (9.9 kcal mol(-1)) than the neutral counterpart. Thus, the 1,3-sigmatropic rearrangement is preferred for the molecular cation, and OCNCO+ and NS+ is produced by subsequent dissociation of the rearrangement product. The analysis agrees very well with the experimental mass spectrum.

Feasibility of higher-order differential ion mobility separations using new asymmetric waveforms.

Technologies for separating and characterizing ions based on their transport properties in gases have been around for three decades. The early method of ion mobility spectrometry (IMS) distinguished ions by absolute mobility that depends on the collision cross section with buffer gas atoms. The more recent technique of field asymmetric waveform IMS (FAIMS) measures the difference between mobilities at high and low electric fields. Coupling IMS and FAIMS to soft ionization sources and mass spectrometry (MS) has greatly expanded their utility, enabling new applications in biomedical and nanomaterials research. Here, we show that time-dependent electric fields comprising more than two intensity levels could, in principle, effect an infinite number of distinct differential separations based on the higher-order terms of expression for ion mobility. These analyses could employ the hardware and operational procedures similar to those utilized in FAIMS. Methods up to the 4th or 5th order (where conventional IMS is 1st order and FAIMS is 2nd order) should be practical at field intensities accessible in ambient air, with still higher orders potentially achievable in insulating gases. Available experimental data suggest that higher-order separations should be largely orthogonal to each other and to FAIMS, IMS, and MS.

ソフトイオン化質量分析による脂質の網羅的, 特異的検出

エレクトロスプレーイオン化 (ESI) やマトリックス支援型レーザー脱離イオン化 (MALDI) などに代表されるソフトなイオン化法を用いた質量分析法は, 微量成分を混合物中においても検出できるという点で, ある特定の分子群にフォーカスをおいた網羅的解析には非常に有効な手段となり得る。その対象分子として, 我々は特にリン脂質に注目して研究を進めている。リン脂質は, 生体膜の構成成分としてだけではなく, シグナリングのメディエーターや受容体のリガンドとしてなど, 生体内で非常に重要な役割を担っているが, 分子種レベルでの特異性など未だに不明な部分は多く, 現在これらの解明が急がれている。このような分野において, 質量分析 (MS) を適用していくには, 多種多様に存在する機種の中から一番適したものを選択する必要がある。それだけではなく, 液体クロマトグラフィーと組み合わせる方法 (LC-MS) やフラグメント情報を得るモード (MS/MS) などをうまく用いていく必要がある。そこで本総説では, 現在主に使用されている代表的なMSの特徴とともに, 脂質研究の分野におけるMSの適用法を紹介する。

Composition and Analysis of Mineral Oils and Other Organic Compounds in Metalworking and Hydraulic Fluids

Metalworking fluids (MWFs) are the primary source of organic contaminants in oily wastewater at many manufacturing facilities. Such facilities, including those in the automotive industry, face the continuing challenge of improving wastewater treatment for organics. Hydraulic fluids (HFs), chemically similar to MWFs, have been a major source of costly soil contamination at industrial and commercial facilities.A better understanding of these organics is essential to the treatment of oily wastewater and HF decontamination. Therefore, two aspects were reviewed: (1) current and historical organic chemical compositions of MWFs and HFs and (2) existing and emerging analytical methods. Base mineral oils were emphasized, as they are the primary ingredient of these fluids and the main contaminant in oily wastewater and HF-contaminated soil. Hydrocarbon compositions of “naphthenic” (cycloalkanes) and “paraffinic” (straight and branched noncyclic alkanes) mineral oils were described, as were the chemical nature of the various MWF and HF additives.Analytical methods for gross organic measurements, individual organics, and structure- and sizebased fractions and distributions were reviewed. Most promising for characterizing the base oil fraction were gas chromatography (GC) coupled with two soft ionization mass spectrometry detection methods and comprehensive 2-dimensional GC. These methods can provide complete distributions of hydrocarbon structures and sizes and are potentially useful to monitor hydrocarbon fate in wastewater treatment, soil/sediment remediation, or other applications involving complex hydrocarbon mixtures.

Laser-assisted Analytical Chemistry and Mass Spectrometry

This article summarizes the current research of our group. Our activities are focused in three main areas, (i) the application of soft ionization mass spectrometry to a range of analytical problems, (ii) the development and fundamental understanding of laser mass spectrometric methods and processes, and (iii) the development of near-field optical microscopy and spectroscopy for nanodiagnostic and nanoanalytical purposes. References to the original literature from our group are given. Extended and continuously updated information can be found in these references as well as on our group web page under http://www.ceac.ethz.ch/zenobi/.

Analysis of glycated proteins by mass spectrometric techniques: qualitative and quantitative aspects.

The analysis of protein glycation poses a difficult challenge due to the complex nature of the reaction. Of the several methods developed for the qualitative and quantitative evaluation of the glycation reaction between proteins and reducing sugars, soft ionization mass spectrometry is the most direct and reliable. In this paper we review the major mass spectrometric methods (ESI and MALDI mass spectrometry) used in the study of protein glycation. We also tested the assumption that limited glycation has little or no effect on the ionization potential of proteins and that the distribution profile of molecular ion peaks of different glycoforms in a mass spectrum reflect their solution composition in a mixture. The results confirm the validity of the above assumption under dilute solution conditions (0.2-0.6 g/ml total protein). A comparison of ESI and MALDI mass spectrometry in the analysis of protein glycation showed that both methods provide qualitative and quantitative analytical results, but the choice of instrument depends on the nature of the sample to be analysed, the level of accuracy and the type of information that is required.

Isolation and Characterization of Two Furan‐side Photoadducts of 7‐Methylpyrido[3,4‐c] Psoralen to the Sugar Moiety of 2‐Deoxyadenosine†

Abstract. The UVA‐mediated photoreaction of the monofunctional 7‐methylpyrido[3,4‐c]psoralen (MePyPs) with 2′‐deoxy‐adenosine was investigated in the dry state. Two main 7‐methylpyrido[3,4‐c]psoralen monoadducts to 2′‐deoxy‐adenosine were isolated by HPLC and characterized by soft ionization mass spectrometry (fast atom bombardment) and extensive 1H NMR analyses including correlation spectroscopy, total correlation spectroscopy and nuclear Overhauser effect measurements. The two unusual photoadducts exhibit a covalent bond between the C‐4′ of the furan moiety of the psoralen on one hand and either the C‐l' or the C‐4′ of the furanose ring of the purine nucleoside on the other hand. The furan‐side monoadducts appear to be specific for both 2′‐deoxy‐adenosine and MePyPs. They are likely to result from the recombination of the 4′,5′‐dihydrofuran‐4′‐yl radical of MePyPs with 2′‐deoxyadenosyl carbon‐centered sugar radicals at either the 1′ or the 5′ position.

Analysis of plant glycoproteins by matrix-assisted laser desorption ionisation mass spectrometry: Application to the N-glycosylation analysis of bean phytohemagglutinin

Matrix-assisted laser desorption ionisation-time of flight (MALDI-TOF) spectrometry is a recently developed soft ionisation mass spectrometry technique which appears as a highly efficient tool for the N-glycosylation analysis of glycoproteins. The potentiality of this analytical technique is illustrated through the analysis of the N-glycosylation of the isolectin L of bean phytohemagglutinin (PHA-L). The analysis was carried out on the native PHA-L as well as on the N-glycans released from this lectin. Furthermore, the two glycopeptides containing the potential N-glycosylation sites prepared by proteolytic cleavage of PHA-L and purified by HPLC were analysed by MALDI-TOF. This study has confirmed that PHA-L is N-glycosylated by two populations of oligosaccharides, high-mannose-type N-glycans and paucimannosidic-type N-glycans, located on Asn-12 and Asn-60, respectively, and has pointed out the microheterogeneity of the glycans N-linked on both Asn residues.

Structural Elucidation of Phospholipids by Soft-ionization Mass Spectrometry

Advances in structure elucidation of glycero-and sphingo-phospholipids including phosphonolipids by soft ionization mass spectrometry for the past eight years are reviewed. This method enables identification of phospholipid class (polar head group), molecular weight, and molecular species of the hydrophobic moiety that includes total carbon number, number and position of double bond, and positional isomer (sn-1 or sn-2) of constituent fatty acids. As soft-ionization technique, ionization by fast atom bombardment (FAB), electrospray (ES) or matrix assisted laser desorption (MALD) are described on its principle, method and information obtained from its yielded molecular ions, fragment ions and product ions that are produced from MS/MS of precursor ion. The mass spectrometer referred are magnetic sector, quadrupole, time-of-flight and Fourier-transform ion cyclotron resonance types. Diacyl and ether-linked species were differentiated by the presence of only one carboxylate ion in the ether-linked species.

Modern mass spectrometry for coatings

For the analysis of polymers soft ionization mass spectrometry, in which only molecular ions are observed, can provide the complete distribution of chains (length, composition, end-groups) in under ten minutes on microgram quantities of material. Moreover, molecular ion information of neat organic pigments or those present in crosslinked networks can also be furnished. No other analytical technique can supply these data in such a short time. The application of mass spectrometry to the characterization of materials used in today's high performance automotive coatings is presented. These include functional monomers, several acrylic copolymers, organic pigments and an epoxide prepolymer. While there are a variety of mass spectrometric techniques, in this paper we will highlight the techniques that we have found useful for the characterization of organic coating components. The selection of the mass spectrometric technique is dictated by the molecular weight of the material and to a lesser extent the chemical composition. We used potassium ionization of desorbed species (K+IDS) performed on a quadrupole mass spectrometer for materials under 1000 Daltons (Da). However, many of the ingredients used in current automotive finishes fall between 1000 and 10 000 Da. For these materials we used a Fourier transform mass spectrometer (FTMS) which is well suited for this mass range and boasts the highest resolution and mass accuracy available. Direct desorption/ionization using a carbon dioxide laser is our standard method of sample introduction. Recently, we coupled a gel permeation chromatograph to our FTMS using an electrospray ionization interface. This hyphenated technique offers one of the most powerful characterization methods for the coatings chemist.

The Characterization of Mutant Proteins in Body Fluids by Soft-Ionization Mass Spectrometry

The Characterization of Mutant Proteins in Body Fluids by Soft-Ionization Mass Spectrometry

ＢＭＳ 質量分析による変異蛋白質の迅速検出と臨床検査への応用

The soft ionization mass spectrometry such as MALDI-TOF and ESI are powerful tools for the detection of proteins, peptides and other biological molecules in body fluids. Since biologically active compounds occur at very low concentrations in mixtures containing salts, there has arisen the need for some special sample handling techniques. In this study, we described some simple preparations for the detection of abnormal proteins in blood and urine prior to the analysis by MALDI-TOF and ESI mass spectrometry.First, by only dilution with distilled water to 10-150 times, albumin and the incomplete immunoglobulin heavy chain in sera and albumin, Bence Jones protein, β2-microglobulin, hemoglobin and lysozyme in urine from patients with nephritis, monoclonal gammopathy and monocytic leukemia were clearly detected. Second, adsorption of albumin with Blue gel or IgG with Protein G Sepharose 4FF could be improved the sensitivities and signal-to-noise ratios for the detections of these proteins. Finally, by immunoprecipitations with specific antisera, proteins at lower concentrations, such as carbohydrate deficient transferrin, could be easily detected using MALDI-TOFMS as well as on-line HPLC/ESIMS analysis.As to the analysis of variant hemoglobinopathy, the peptides prepared by digestion of intact globin were analyzed and nearly 90 significant peaks were detected by a single spectrum from ESI analysis. Ion peaks which were assigned with some degree of certainly covered whole sequence from a- and b-subunits. Especially, at the analysis of a variant hemoglobin “core”, the free cystein residue would be converted into cysteic acid by performic acid oxidation before enzymatic cleavage, which would increase the recoveries of the peptides in the “core” regions. The tandem mass spectrometry with oxidized globin mixture digested with trypsin and lysyl endopeptidase will offer a standard method to detect substitution in the “core” region of hemoglobin.

Direct Analysis of Elastomer Compounds by Soft Ionization, Tandem (MS/MS) and High Resolution (AC-MS) Mass Spectrometry

Abstract In recent years very effective mass spectrometric methods have been developed for direct polymer compound analysis. The high sensitivity, high specificity, and superb mixture analysis capabilities of modern mass spectrometry make it an invaluable tool in the polymer industry, particularly for qualitative analysis (chemical identification) of organic additives as well as polymeric components. “Survey” mass spectra obtained with soft ionization methods — field ionization (FI-MS) and chemical ionization (CI-MS) — provide diagnostic overviews of chemical composition. The supplemental tandem (MS/MS) and atomic composition (AC-MS) techniques are used to make specific identifications of various organic ingredients. This report describes the direct mass spectrometric analysis of three different elastomer compounds. Organic additives, including curatives, were identified via thermal desorption methods in a commercial EPDM bearing as well as a diene rubber V-belt. The composition of a commercial thermoplastic polyurethane was determined via pyrolysis (Py-CI-MS). These problem-solving examples illustrate the very effective role that mass spectrometry can play in the industrial polymer analysis laboratory.

Quadrupole mass spectrometry in combination with lithium ion attachment for sampling at atmospheric pressure: possible coupling to supercritical fluid chromatography

A novel device has been developed which permits sampling at atmospheric pressure followed by soft ionization mass spectrometry. Sample gases are introduced through a small aperture at atmospheric pressure into an ionization reaction chamber containing a lithium ion emitter. In this ionization reaction chamber, lithium ion attachment to the molecule takes place. The ionized adduct is detected by a quadrupole mass spectrometer. With this instrument incorporating soft ionization, it should be possible at atmospheric pressure to detect any chemical species, including radical intermediates, on a real time basis

Peptide-metal ion interactions in solution: Detection by laser desorption time-of-flight mass spectrometry and electrospray ionization mass spectrometry

The specific interaction of Cu(II) ions with metal-binding peptides in solution has been investigated by two different methods of soft ionization mass spectrometry, namely matrix-assisted ultraviolet laser desorption time-of-flight mass spectrometry (LDTOF) and electrospray ionization mass spectrometry (ES). The metal-binding peptide selected for these investigations is a 26-residue sequence found on the surface of the human plasma metal-transport protein histidine-rich glycoprotein. The peptide, (GHHPH)5 G, was synthesized and evaluated by ES and LDTOF before and after the addition of Cu(II) or Mn(II) ions in solution. In the absence of added metal ions, the peptide was observed to have a mass equal to within 0.5 Da of its calculated mass (2903.0 Da) by both LDTOF and ES. In the presence of Cu(II), up to five additional peaks were observed at mass increments of approximately 63.9 Da (LDTOF) or 62.3 Da (ES); Mn was not bound to the peptide under identical experimental conditions. By both LDTOF and ES, the maximum Cu-binding capacity observed (i.e., 5 g-atoms mol−1) demonstrated that up to 1 Cu could be bound per (GHHPH) internal repeat unit. This peptide-metal ion interaction stoichiometry was verified by direct titration in solution and, with immobilized peptide, by quantitative metal ion affinity chromatography. Thus, the ability to detect stable peptide-metal complexes did not appear to be differentially affected by the two different volatilization/ionization methods needed to generate charged intact molecular ions. The quantity and stoichiometry of bound Cu atoms was affected, however, by experimental conditions such as LDTOF matrix and ES solution composition. These results demonstrate the ability to verify directly the solution-phase binding capacity of metal-binding peptides by LDTOF and by ES. We conclude from these studies that other metallo-organic interactions may also be amenable to investigation by these rapid and sensitive techniques.

Model protein surface domains for the investigation of metal ion-dependent macromolecular interactions and biospecific metal ion transfer

We describe the use of surface-immobilized transition metal ions not only as tools for the site-specific immobilization and purification of peptides and proteins but also as probes of altered macromolecular surface architecture. Although we present examples of the use of traditional immobilized chemical chelators (e.g., iminodiacetate) for these purposes, we also introduce methods for identifying and using natural metal-binding domains derived from protein surfaces to immobilize metal ions in a biospecific manner. Such model protein surfaces facilitate the investigation of the mechanisms by which metal ions influence the interaction of macromolecules. This approach, immobilized metal-binding domain recognition, depends on the proficient identification and characterization of individual protein surface metal-binding domains. To facilitate this process, we have developed the use of two different forms of soft ionization mass spectrometry to observe intact peptide-metal ion complexes; this enables the mass-dependent identification of specific metal-binding sequences. Model protein surfaces constructed thus far and found to exhibit metal ion-dependent macromolecular recognition specificity include (i) a series of immobilized peptides (GHHPH) n G, which define the surface metal-binding domain (G365-H389) of the human plasma metal ion transport protein known as histidine-rich glycoprotein; (ii) the immobilized dimerization domain (D473-L525) from the human estrogen receptor protein; (iii) the immobilized “zinc-finger” DNA-binding domain (K180-M250) of the human estrogen receptor; and (iv) the immobilized iron-binding domain (R1-K18) derived from the N-terminus of human β-casein. We discuss the investigation of metal ion-dependent interactions between macromolecules and the transfer of metal ions between macromolecules.