ZnS nanomaterial characterization by MALDI-TOF mass spectrometry

We present a methodology for mass and size dispersity analysis by MALDI-TOF mass spectrometry of lyothermally grown 2.5-3.7 nm ZnS nanocrystals having a Zn blende crystal structure. These results correlate with information obtained by TEM and absorption spectroscopy. The use of MS methods to probe size and size dispersity provides a convenient method to rapidly analyze II-VI materials at the nanoscale. We believe these results represent the first mass spectrometric analysis of size and size dispersities on II-VI nanocrystals.     

Coal characterization by on-line pyrolysis-field ionization mass spectrometry

Summary Pyrolysis-field ionization mass spectrometry (Py-FIMS) was used for the first time to directly characterize Chinese coals and their extracts. The summed mass spectra (about 30 magnetic scans) of four coal samples and the dimethylformamide extracts of two very different coals were registered between 50° and 750°C using linear heating in high vacuum (10^–3 Pa) and approximately 6 min temperature rise time. Utilizing temperature-programmed pyrolysis and FI as soft ionization mode, the spectra displayed almost exclusively molecular ions of the evolved products. The thermograms, i.e. the intensities of the total ion current and selected ions were plotted versus the scan number, heating time and temperature. In general, two maxima in these thermograms were observed, which were different for the coals and reflected their carbon/hydrogen content. Comparing the mass spectra of the low temperature part (first maximum) with summed spectra of the extracts shows an interesting similarity. In contrast, the high temperature part (second maximum) indicates the products of thermo-degradation. The applied method is a fast and convenient tool for the characterization of evolved volatiles and thermal degradation products of coals and coal extracts.

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Kennzeichnung von Kohlen mit direkter Pyrolyse und Feldionisations-Massenspektrometrie

     

Top-down identification and characterization of biomolecules by mass spectrometry

The most widely used modern mass spectrometers face severe performance limitations with molecules larger than a few kDa. For far larger biomolecules, a common practice has been to break these up chemically or enzymatically into fragments that are sufficiently small for the instrumentation available. With its many sophisticated recent enhancements, this "bottom-up" approach has proved highly valuable, such as for the rapid, routine identification and quantitation of DNA-predicted proteins in complex mixtures. Characterization of smaller molecules, however, has always measured the mass of the molecule and then that of its fragments. This "top-down" approach has been made possible for direct analysis of large biomolecules by the uniquely high (>10(5)) mass resolving power and accuracy ( approximately 1 ppm) of the Fourier-transform mass spectrometer. For complex mixtures, isolation of a single component's molecular ions for MS/MS not only gives biomolecule identifications of far higher reliability, but directly characterizes sequence errors and post-translational modifications. Protein sizes amenable for current MS/MS instrumentation are increased by a "middle-down" approach in which limited proteolysis forms large (e.g., 10 kDa) polypeptides that are then subjected to the top-down approach, or by "prefolding dissociation." The latter, which extends characterization to proteins >200 kDa, was made possible by greater understanding of how molecular ion tertiary structure evolves in the gas phase.     

Structural characterization of glycoporphyrins by electrospray tandem mass spectrometry

Porphyrin derivatives having a galactose or a bis(isopropylidene)galactose structural unit, linked by ester or ether bonds, were characterized by electrospray tandem mass spectrometry (ES-MS/MS). The electrospray mass spectra of these glycoporphyrins show the corresponding [M + H](+) ions. For the glycoporphyrins with pyridyl substituents and those having a tetrafluorophenyl spacer, the doubly charged ions [M + 2H](2+) were also observed in ES-MS with high relative abundance. The fragmentation of both [M + H](+) and [M + 2H](2+) ions exhibited common fragmentation pathways for porphyrins with the same sugar residue, independently of the porphyrin structural unit and type of linkage. ES-MS/MS of the [M + H](+) ions of the galactose-substituted porphyrins gave the fragment ions [M + H - C(2)H(4)O(2)](+), [M + H - C(3)H(6)O(3)](+), [M + H - C(4)H(8)O(4)](+) and [M + H - galactose residue](+). The fragmentation of the [M + 2H](2+) ions of the porphyrins with galactose shows the common doubly charged fragment ions [porphyrin + H](2+), [M + 2H - C(2)H(4)O(2)](2+), [M + 2H - C(4)H(8)O(4)](2+), [M + 2H - galactose residue](2+) and the singly charged fragment ions [M + H - C(3)H(6)O(3)](+) and [M + H - galactose residue](+). The fragmentation of the [M + H](+) ions of glycoporphyrins with a protected galactosyl residue leads mainly to the ions [M + H - CO(CH(3))(2)](+), [M + H - 2CO(CH(3))(2)](+), [M + H - 2CO(CH(3))(2) - CO](+), [M + H - C(10)H(16)O(4)](+) and [M + H - protected galactose](+). The doubly charged ions [M + 2H](2+) fragment to give the doubly charged ions [porphyrin + H](2+) and the singly charged ions [M + H - protected galactose residue](+) and [M + H - CO(CH(3))(2)](+). For the porphyrins where the sugar structural unit is linked by an ester bond, [M + 2H](2+), ES-MS/MS showed a major and typical fragmentation corresponding to combined loss of a sugar structural unit and further loss of water, leading to the ion [M + 2H - sugar residue - H(2)O](2+), independently of the structure of the sugar structural unit. These results show that ES-MS/MS can be a powerful tool for the characterization of the sugar structural unit of glycoporphyrins, without the need for chemical hydrolysis.     

Analysis of some commercial polysorbate formulations using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Analyses of polysorbate formulations (Tween 20, Tween 40, Tween 60, and Tween 80) by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) reveal a complex mixture of oligomers that include polyethylene glycols, polyethylene glycol esters, isosorbide polyethoxylates, sorbitan polyethoxylates, polysorbate monoesters, polysorbate diesters, and sorbitol polyethoxylate esters. The MALDI-TOF mass spectra for these formulations show the presence of sodiated molecules in which the major signals are attributed to the presence of polyethylene glycols, isosorbide polyethoxylates, and sorbitan polyethoxylates. Additionally, the complexity of the spectra was correlated to the constituent fatty acid moieties in the polysorbate formulations. Thus Tween 20 showed the presence of polysorbate monolaurates, polysorbate monomyristates, and polysorbate monopalmitates. Tween 40 contained polysorbate mono- and dipalmitates. Tween 60 contained polysorbate monopalmitates and polysorbate monostearates. For the Tween 80, mass assignment for polysorbate monooleates and polysorbate dioleates was equivocal, because both of these oligomeric series have the same molecular weight as the sorbitan polyethoxylates, and thus the Tween 80 MALDI-TOF spectrum appeared to be the least complicated of the four commercial polysorbate formulations.     

Comprehensive characterization of rodenticides in wastewater by liquid chromatography-tandem mass spectrometry

Rodenticides are used as pest control to eradicate rodents and have emerged as new environmental contaminants due to their widespread use in domestic and urban infrastructures. In this study, we have developed and validated an analytical methodology based on liquid chromatography-tandem mass spectrometry (LC-MS/MS) for the determination of 13 anticoagulant rodenticides in wastewater. In a first step, ionization conditions were tested in electrospray mode, and positive ionization gave the highest sensitivity. Fragmentation patterns were determined and two selected reaction monitoring (SRM) transitions were selected for each compound. Using a Zorbax Eclipse XDB-C18 column and specific SRM transitions, 13 compounds were resolved. The LC-MS/MS method provided good linearity, sensitivity, intra- and inter-day precision, and good identification capabilities for these compounds in wastewaters. Thereafter miniaturized liquid–liquid extraction (LLE) and solid-phase extraction (SPE) were optimized. Oasis HLB and Strata WA SPE cartridges with methanol/dichloromethane as eluting solvents provided good recoveries and limits of detection ranged between 0.34 and 20 ng L^?1, whereas LLE failed to recover some compounds. Finally, the performance of both LLE and SPE methods was evaluated by analyzing rodenticides in a set of wastewaters. Warfarin was the only detected compound at nanogram per liter level, and good agreement was observed between LLE and SPE.     

Structural characterization of mono- and bisphosphonium salts by fast atom bombardment mass spectrometry and tandem mass spectrometry

Positive-ion fast atom bombardment (FAB) mass spectra are reported for a representative series of mono- and bisphosphonium halides derived from triphenylphosphine. The mass spectra of the monoalkyltriphenylphosphonium salts typically contain abundant intact cations that can be used to establish the cationic relative molecular mass and diagnostic fragment ions that allow the characterization of structural subgroups. Depending on the functional group substitution on the alkyl group, additional fragment ions are observed which are formed by loss of small neutral molecules from the intact cation and that can be used for the differentiation of isomeric phosphonium salts. Molecular dication are typically observed in the FAB mass spectra of the bisphosphonium salts when they are analysed in 3-nitrobenzyl alcohol. In addition, production of singly charged ions by clustering with a counter ion, decomposition involving removal of one of the charge centres and one-electron reduction are generally observed. Structurally diagnostic fragments are also obtained. The fragmentation pathways of the ions derived from the phosphonium salts were elucidated by precursor ion and product ion tandem mass spectrometric experiments. For the phosphonium salts containing a long-chain hydrocarbon alkyl group, high-energy collision-induced decomposition of the intact cation is needed to obtain unambiguous structural information.     

Detection and characterization of hydroxyl radical adducts by mass spectrometry

The study of the influence of free radicals in the biological process depends primarily on the capacity to detect these reactive species. In this work we have studied the application of mass spectrometry to the identification of hydroxyl radical species. The detection and identification by collisional activation mass-analyzed ion kinetic energy spectrometry (CA-MIKES) of a spin adduct of DMPO with the hydroxyl radical [(DMPO + O) + H]+ (m/z 130) has demonstrated that mass spectrometry can be a powerful tool in the detection and identification of spin adducts of DMPO with hydroxyl radical species. We were also able to detect the capture of secondary free radicals using ethanol by detecting and identifying the corresponding adduct [(DMPO + ethanol) + H]+. Other spin adducts have also been detected and identified. We consider that the use of mass spectrometry is a relevant technique for the detection of free hydroxyl radicals, especially in complex mixtures, since mass spectrometry is able to discriminate these adducts in such situations. Moreover, using this approach, it was possible to identify new spin adducts.     

Structural characterization of phosphatidylcholines by atmospheric pressure photoionization mass spectrometry

The potential of atmospheric pressure photoionization was investigated for the structural analysis of phosphatidylcholine lipids (PCs). [M+H]+ ions of high abundance were obtained, along with several fragment ions. Three of these dissociation products corresponded to quite unusual fragmentation pathways but allowed the determination of both the nature and the position on the glycerol backbone (sn-1 or sn-2) of the fatty acyl chains. The loss of a methyl group from the choline head was also observed. These results suggest a complex ionization mechanism in APPI. However, this method proved to be very powerful for the rapid structural analysis of PC species without using MS/MS experiments.     

Simultaneous thermogravimetry and mass spectrometry in polymer characterization

The assembly and operation of a simple, directly coupled thermobalance and quadrupole mass spectrometer are described. Usefulness of the method and ease of operation are illustrated by the decomposition of TDI and MDI polyurethanes, ABS plastic and a capped and uncapped polyester.     

Mass spectrometry characterization of the glycation sites of bovine insulin by tandem mass spectrometry

Bovine insulin was glycated under hyperglycemic reducing conditions and in nonreducing conditions. Purification through HPLC allowed isolating glycated forms of insulin and a novel triglycated form (6224.5 Da) was purified. Endoproteinase Glu-C digestion combined with mass spectrometry (MALDI-TOF/TOF) allowed determining the exact location of the glycation sites in each of the isolated glycated insulins. For the first time, a triglycated form of insulin was isolated and characterized accordingly to its glycation sites. These glucose binding sites were identified as the N-terminals of both chains (Gly1 and Phe1) and residue Lys29 of B-chain. Moreover, in diglycated insulin we found the coexistence of one specie glycated at the N-terminals of both chains (Gly1 and Phe1) and another specie containing the two glucitol adducts in B-chain (Phe1 and Lys29). Also, in monoglycated insulin generated in reducing and nonreducing conditions, one specie glycated at Phe1 and another specie glycated at Lys29, both B-chain residues coexist.     

Structural characterization of acetylpyridinium-ethyl pyruvate adducts by electrospray ionization mass spectrometry

The reactions of ethyl pyruvate with acetic anhydride and pyridine were studied by electrospray ionization mass spectrometry (ESI-MS). Ethyl 2-acetoxy-2-pyridiniumpropionate (1) (m/z 238) resulting from the reaction of the acetylpyridinium cation with ethyl pyruvate, and the adduct of ethyl 2-acetoxyacrylate with a pyridinium cation (2), bound together by non-covalent interactions (m/z 238), were identified by ESI-MS for the first time. Structures 1 and 2 cannot be distinguished, probably because one may be converted into the other and vice versa.     

Structural characterization of complex bacterial glycolipids by Fourier transform mass spectrometry

Bacterial glycolipids are complex amphiphilic molecules which are on the one hand of utmost importance for the organization and function of bacterial membranes, and which on the other hand play a major role in the activation of cells of the innate and adaptive immune system of the host. Already small alterations of their chemical structure may influence the biological activity tremendously. Due to their intrinsic biological heterogeneity [number and type of fatty acids, saccharide structures, and substitution with e.g. phosphate (P), 2-aminoethyl- (pyro)phosphate groups (P-Etn) or 4-amino-4-deoxyarabinose (Ara4N)], separation of the different components are a prerequisite for unequivocal chemical and NMR structural analyses. In this contribution the structural information which can be obtained from heterogeneous samples of glycolipids by Fourier transform (FT) ion cyclotron resonance mass spectrometric methods is described. By means of recently analysed complex biological samples the possibilities of high resolution electrospray ionization FT-MS are demonstrated. Capillary skimmer dissociation, as well as tandem mass spectrometry MS/MS analysis utilizing collision-induced dissociation and infrared multiphoton dissociation, are compared and their advantages to provide structural information of diagnostic importance are discussed.     

Fast characterization of foodstuff by headspace mass spectrometry (HS-MS)

The field of the rapid characterization of products by HS-MS is reviewed. The general principle of HS-MS systems consists of introducing volatile components present in the HS of a sample without prior chromatographic separation into the ionization chamber of a mass spectrometer. The spectrum resulting from simultaneous ionization and fragmentation of the mixture of molecules introduced constitutes a “fingerprint” that is characteristic of the product being analyzed. Exploitation of this spectral information allows one determine the composition of the sample.     

Electrospray mass spectrometry in the structural characterization of cephalosporins

Six cephalosporins of pharmacological interest, cephalexin, cephuroxime, cephazolin, cephoperazone sodium salt, cephatrizin free acid and cephonicid disodium salt, were analysed by electrospray mass spectrometry. [M - Na]- anions were produced in high yield in the case of cephalexin, cephuroxime, cephazolin and cephoperazone, leading to signals at least two orders of magnitude more intense than those related to [M + Na]+ cations observed in the positive ion mode. In cephatrizin, [M - H]- represented the most abundant species, whereas in cephonicid the [M - 2Na + H]- anions were easily produced. No fragment ions were detectable in the electrospray spectra of any of the compounds, and MSn turned out to be essential to draw the fragmentation patterns. Most of these patterns were related to the substituent of the 7-aminocephalosporin nucleus, suggesting that the nucleus itself is highly stable.     

Structural characterization of reactive dyes using liquid secondary ion mass spectrometry/tandem mass spectrometry

Reactive Blue 19 (RB 19), its reactive form (RB 19-VS) and its hydrolyzed form (RB 19-OH) were examined using liquid secondary ion mass spectrometry/tandem mass spectrometry (LSIMS/MS/MS) in the negative-ion mode under low-energy collision conditions (240–300 eV). Structurally characteristic fragment ions were obtained, none of which has been previously reported for these reactive dyes. Among the ions obtained were SO₃^? ions, ions due to central amino cleavage and reactive group cleavage, and ions due to loss of SO₃ and SO₂. Possible pathways for the formation of product ions are proposed. The structural information obtained should help to characterize and identify reactive dyes better.     

Multiple-stage mass spectrometry in structural characterization of organophosphorus compounds

Multiple-stage mass spectrometry involving consecutive collision-activated dissociation reactions was used to examine the structures of fragment ions commonly formed on electron ionization of organophosphorus esters. The compounds studied include several aryl thiophosphates, some of which are analogs of common pesticides. Energy-resolved collisionactivated dissociation experiments allow the dissociation of the molecular ions of these compounds in such a manner that only a few fragment ions dominate the spectrum. An abundant fragment ion of m/z 109, formed from all of the compounds studied, can have at least four different stable structures: (CH₃O)₂PO⁺, CH₃CH₂OP(O)OH⁺, CH₂ =CHOP(H)(OH)₂ ⁺, and (CH₂O)₂P(H)OH⁺. The structure of the fragment ion of m/z 109 was found to reflect the phosphorus-containing part of the compounds studied. Another abundant fragment ion obtained for all the aryl esters studied is structurally characteristic of the aromatic moiety of the molecule. This fragment ion is the result of a complex rearrangement involving transfer of an alkylene group to the aromatic ring from the phosphoruscontaining part of the molecular ion. The utility of these fragment ions in the structural characterization of unknown organophosphorus esters is discussed.     

Emerging methods in proteomics: top-down protein characterization by multistage tandem mass spectrometry

"Top-down" mass spectrometry methods have emerged as an attractive alternative to conventional "bottom-up" approaches for the comprehensive characterization of co- and post-translational protein modifications. Here we present a brief overview of current strategies employed for top-down protein characterization and discuss the key technical challenges and solutions associated with their implementation on a range of mass spectrometry instrument platforms. For more specific details regarding the individual strategies described herein, interested readers are referred to the references cited at the end of this article.