A pyrolysis mass spectrometry study of polythiophene copolymers

The thermal behaviour of copolymers of thiophene with decanedioic acid bis-(2-thiophen-3-yl-ethyl)ester (DATE) and terephthalic acid bis-(2-thiophen-3-yl-ethyl)ester (TATE) prepared by potentiostatic polymerization was studied via pyrolysis mass spectrometry. It was determined that the electrolytic films correspond to the related homopolymers. The increase in thermal stability of ester linkages, and evolution of characteristic degradation products of TATE and DATE together with thiophene based products above 400 °C confirmed copolymer formation.     

Direct pyrolysis mass spectrometry of diphenyl methyl allophanate

The thermal decomposition mechanism of α,γ-diphenyl methyl allophanate as a model compound for the crosslinking site in polyurethane networks was investigated by direct pyrolysis in the mass spectrometer. The primary degradation reactions were dissociation of allophanate into isocyanate and urethane followed by dissociation of the urethane produced into isocyanate and alcohol. However, decarboxylation of the urethane fragment also took place slowly.     

Direct pyrolysis mass spectrometry studies on thermal degradation characteristics of poly(phenylene vinylene) with well-defined PSt side chains

Thermal degradation characteristics of a new macromonomer polystyrene with central 4,4′-dicarbaldehyde terphenyl moieties and poly(phenylene vinylene) with well-defined polystyrene (PPV/PSt) as lateral substituents were investigated via direct pyrolysis mass spectrometry. A slight increase in thermal stability of PSt was detected for (PPV/PSt) and attributed to higher thermal stability of PPV backbone. It was almost impossible to differentiate products due to the decomposition of PPV backbone from those produced by degradation of PSt.     

Dansyl labeling and bidimensional mass spectrometry to investigate protein carbonylation

Carbonylation is a non-enzymatic irreversible post-translational modification. The adduction of carbonyl groups to proteins is due to the presence of excess of ROS in cells. Carbonylation of specific amino acid side chains is one of the most abundant consequences of oxidative stress; therefore, the determination of carbonyl groups content in proteins is regarded as a reliable way to estimate the cellular damage caused by oxidative stress. This paper reports a novel RIGhT (Reporter Ion Generating Tag) (A. Amoresano, G. Monti, C. Cirulli, G. Marino. Rapid Commun. Mass Spectrom. 2006, 20, 1400) approach for selective labeling of carbonyl groups in proteins using dansylhydrazide, coupled with selective analysis by bidimensional mass spectrometry. We first applied this approach to ribonuclease A and lysozyme as model proteins. According to the so-called 'gel-free procedures', the analysis is carried out at the level of peptides following tryptic digest of the whole protein mixture. Modified RNaseA was analyzed in combined MS(2) and MS(3) scan mode, to specifically select the dansylated species taking advantage of the dansyl-specific fragmentation pathways. This combination allowed us to obtain a significant increase in signal/noise ratio and a significant increase in sensitivity of analysis, due to the reduction of duty cycle of the mass spectrometer. The unique signal obtained was correlated to peptide 1-10 of RNaseA carbonylated and labeled by dansylhydrazide. This strategy represents the first method leading to the direct identification of the carbonylation sites in proteins, thus indicating the feasibility of this strategy to investigate protein carbonylation in a proteomic approach.     

Time-resolved measurements of individual ion cloud signals to investigate space-charge effects in plasma mass spectrometry

A new approach to directly monitor space charge induced effects due to high concentrations of efficiently ionized elements in inductively coupled plasma mass spectrometry (ICP-MS) is described. The broadening of ion clouds produced from individual, monodisperse drops of sample is measured by using time-resolved ICP-MS. The extent of broadening due to high concentrations of Pb in the sample is related inversely to the analyte mass. For the lightest analyte investigated, Li⁺, the relative width of the time-resolved analyte peak increases and then shows a dip in the center as the Pb concentration is increased to 500 and then 1500 µg/mL. The initial results of experiments that investigated chemical matrix effects as a function of concomitant species concentration, analyte mass, and sampling location in ICP-MS are consistent with space-charge effects.     

Competition between dopants on redox reaction of polypyrrole

The surface of PPy prepared in a multiple electrolyte solution such as NaDS-NaClO₄ in H₂O shows a coarser structure than that of the polymer prepared in a single electrolyte system. DS⁻ with a large aliphatic chain is used as a dopant in preparation of PPy. The dopant is trapped in PPy when the polymer is reduced in an aqueous system. A cation Na⁺ or K⁺ is inserted into the polymer to balance the free DS⁻ liberated form and remained in it on reduction. PPy doped with DS⁻ shows a high degree of redox reactivity in the system of TBADS-AN but a poor stability in repeated redox process. The degree and rate of redox reactivity enhance when an aqueous solution of NaClO₄ is used as an electrolyte system. Both Na⁺ and ClO₄⁻take part in the redox reaction and the reduction process is intense at only one current potential.     

The examination of some vinyl acetate/olefin copolymers by pyrolysis gas chromatography mass spectrometry.

A study of the thermal degradation of some vinyl acetate/olefin copolymers reveals that side chain scissions at the backbone and scissions within the side chains themselves yield fragments which are apparently characteristic of the parent olefin.     

Pyrolysis analysis of Japanese lacquer films: Direct probe-Li+ ion attachment mass spectrometry versus pyrolysis/gas chromatography/mass spectrometry

Li⁺ ion attachment mass spectrometry (Li⁺IAMS) with a temperature-programmed direct probe allows the analysis of nonvolatile complex natural materials. With this technique, chemical species can be detected at atmospheric pressure in real time, a capability that is particularly useful for analyzing evolved gas products. The products of pyrolysis can be studied by analyzing the mass spectra of degraded samples. Here, we investigated the pyrolysis of Japanese lacquer films (urushi) through temperature-programmed heating using direct probe-Li⁺IAMS. The analyzed sample had a characteristic profile in both the appearance of unique components and the distribution of pyrolysis products. Among the pyrolysis products detected, carboxylic acids, phenols, catechols, and aliphatic and aromatic hydrocarbons were most abundant. We compared our results with those of a previous pyrolysis/gas chromatography/mass spectrometry study of Japanese urushi samples. This comparison demonstrated significant differences between the two techniques in terms of the products and their distributions in the Japanese lacquer films. Our approach offers the opportunity to directly study the pyrolysis processes occurring in complex natural materials and suggests a way to determine the identity of a lacquer source by identifying different types of lacquer monomer.     

Flash-vacuum pyrolysis of 1-acylbenzotriazole: Direct observation of cyclopenta-2,4-dienylidenemethaneimines by tandem mass spectrometry and low-temperature infrared spectrometry

A real-time analysis of the flash-vacuum pyrolysis products of 1-acetylbenzotriazole (1) and 1-benzoylbenzotriazole (2) was performed by tandem mass Spectrometry. In the temperature range 500-600 °C, these compounds lose nitrogen, yielding N-acetyl- and N-benzoylcyclopenta- 2,4-dienylidenemethaneimines (10 and 17, respectively). At higher pyrolysis temperatures, 1 gives 2-methylbenzoxazole, cyanocyclopentadiene, methylcyanocyclopentadiene(s), benzonitrile and ketene, which were identified by collision-activated dissociation mass Spectrometry. Low-temperature infrared experiments confirmed the pyrolytic transformation 1(2) → 10(17) at mediated temperatures.     

Synthesis and characterization of polypyrrole nanofibers with different dopants

Nanostructures of polypyrrole (PPy) were synthesized in the presence of different dopants including hydrochloric acid (HCl), ferric chloride (FeCl₃), p‐toluene sulfonic acid (p‐TSA), camphor sulfonic acid (CSA), and polystyrene sulfonic acid (PSSA), using a simple interfacial oxidative polymerization method. The method is a reliable non‐template approach with relatively simple instrumentation, ease of synthesis, and economic viability for synthesizing PPy nanostructures. Morphology of synthesized PPy structures was investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), which indicate the formation of one‐dimensional (1D) nanofibers with average diameter of 75–180 nm. Energy dispersive spectrum (EDS) of the PPy nanofibers indicates the attachment of the dopants to the PPy backbone; the fact is further confirmed by the Fourier transform infrared (FTIR) spectra of PPy nanostructures. Thermal stabilities of the nanostructures explored using thermal gravimetric analysis (TGA) follow the order PPy‐p‐TSA > CSA > HCl > FeCl₃ > PSSA. It is noticed that the electrical conductivity (EC) of PPy nanostructures depends upon the nature of dopant (PPy‐p‐TSA > CSA > HCl > FeCl₃ > PSSA), PPy‐p‐TSA nanofibers showing the highest EC of 6 × 10^?2 Scm^?1. Copyright © 2009 John Wiley & Sons, Ltd.     

Characterization of chitosan by pyrolysis—mass spectrometry

Chitosan of different degrees of deacetylation have been prepared from chitin. Pyrolysis-mass spectra of these chitosan samples in the ion source of a mass spectrometer were examined to check for a correlation with the degree of deacetylation, as represented by the amine content. The results indicate that as the degree of deacetylation increases, the peak ratios 80:60, 67:60 and 80:42 increase to a limit, representing the limit of deacetylation of chitin. The 80 and 67 fragments originate from the d-glucosamine moiety of the polymer and the 60 and 42 fragments from the N-ethyl-d-glucosamine moiety. For chitin, the predicted values of these ratios are expected to be low when compared to chitosan, and this is borne out by the experimental data.     

Direct pyrolysis in the mass spectrometer of aromatic polysulfonates and polythiosulfonates

The thermal degradation mechanism of three aromatic polysulfonates and polythiosulfonates was investigated by direct pyrolysis in the ion source of a mass spectrometer. Thermal degradation reactions were followed directly by this method by detecting the thermal and electron impact induced fragments. The results obtained have provided evidence that sulfur dioxide extrusion from the polymer backbone takes place in these polymers above 300°C. The synthesis and molecular characterization of the polymers studied are reported in the text.     

Characterization of some penicillins and cephalosporins by pyrolysis mass spectrometry

A number of clinically significant penicillins and cephalosporins have been characterized by pyrolysis mass spectrometry. With only a 2-μg sample of formulated drugs, the antibiotics can be clearly differentiated. The structure of the major fragments is assessed.     

Synthesis and characterization of polypyrrole dispersions prepared with different dopants

Stable polypyrrole dispersions were prepared by chemical oxidative polymerization of pyrrole in an aqueous medium containing different anionic salts - sodium benzoate, potassium hydrogen phthalate and sodium hydrogen succinate. Results of the elemental analysis and FT-IR spectroscopy confirmed that the anionic salts are incorporated in the conducting polymers and functioned as the dopants. The retardation of pyrrole polymerization was observed when a certain amount of the salt was used as dopant. SEM images of polypyrrole dispersions indicate large spherical particles (150-180nm). The conductivity of polypyrrole composites has also been investigated.     

质谱学中的立体化学效应-公桕立体异构体的质谱研究

本文考察了十三个鬼桕毒及其衍生物的立体异构体的质谱性能,借助高分辨质谱裂解方式及特征离子相对丰度的影响,并提出了合理的解释。     

Direct exposure electron ionization mass spectrometry and gas chromatography/mass spectrometry techniques to study organic coatings on archaeological amphorae

Two different analytical approaches, direct exposure electron ionization mass spectrometry (DE-MS) and gas chromatography/mass spectrometry (GC/MS), were compared in a study of archaeological resinous materials. DE-MS was found to be an efficient fingerprinting tool for the fast screening of organic archaeological samples and for providing information on the major components. GC/MS appeared to be more efficient in unravelling the sample composition at a molecular level, despite the long analysis time and the need for a wet chemical pretreatment. Both procedures were applied to characterize the organic material present as coatings in Roman and Egyptian amphorae. DE-MS successfully identified abietanic compounds, hence a diterpenic resinous material could be identified and its degree of oxidation assessed. GC/MS enabled us to identify dehydroabietic acid, 7-oxodehydroabietic acid, 15-hydroxy-7-oxodehydroabietic acid, 15-hydroxydehydroabietic acid, retene, tetrahydroretene, norabietatriene, norabietatetraene and methyl dehydroabietate. These oxidized and aromatized abietanes provided evidence that the amphorae examined were waterproofed with a pitch produced from resinous wood of plants from the Pinaceae family. The chemometric evaluation of the GC/MS data highlighted significant chemical differences between the pitches found in the two archaeological sites, basically related to differences in the production techniques of the materials and in their degradation pathways.     

Application of pyrolysis–mass spectrometry and pyrolysis–gas chromatography–mass spectrometry with electron-ionization or resonance-enhanced-multi-photon ionization for characterization of crude oils

A novel analytical system for gas-chromatographic investigation of complex samples has been developed, that combines the advantages of several analytical principles to enhance the analytical information. Decomposition of high molecular weight structures is achieved by pyrolysis and a high separation capacity due to the chromatographic step provides both an universal as well as a selective and sensitive substance detection. The latter is achieved by simultaneously applying electron ionization quadrupole mass spectrometry (EI-QMS) for structural elucidation and [1 + 1]-resonance-enhanced-multi-photon ionization (REMPI) combined with time-of-flight mass spectrometry (ToFMS). The system has been evaluated and tested with polycyclic aromatic hydrocarbon (PAH) standards. It was applied to crude oil samples for the first time. In such highly complex samples several thousands of compounds are present and the identification especially of low concentrated chemical species such as PAH or their polycyclic aromatic sulfur containing heterocyclic (PASH) derivatives is often difficult. Detection of unalkylated and alkylated PAH together with PASH is considerably enhanced by REMPI–ToFMS, at times revealing aromatic structures which are not observable by EI-QMS due to their low abundance. On the other hand, the databased structure proposals of the EI-QMS analysis are needed to confirm structural information and isomers distinction. The technique allows a complex structure analysis as well as selective assessment of aromatic substances in one measurement. Information about the content of sulfur containing compounds plays a significant role for the increase of efficiency in the processing of petroleum.