Direct analysis of oligomeric tackifying resins in rubber compounds by automatic thermal desorption gas chromatography/mass spectrometry

Two analytical methods, automatic thermal desorption gas chromatography/mass spectrometry (ATD-GC/MS) and pyrolysis gas chromatography/mass spectrometry (Py-GC/MS), were applied as direct methods for the analysis of oligomeric tackifying resins in a vulcanized rubber. The ATD-GC/MS method, based on discontinuous volatile extraction, was found to be an effective means for direct analysis of the oligomeric tackifying resins contained in a vulcanized rubber. The oligomeric tackifying resins, such as t-octylphenolformaldehyde (TOPF) resin, rosin-modified terpene resin, and cashew resin, could be directly analyzed in vulcanized rubber by ATD-GC/MS. Much simpler total ion chromatograms were obtained by ATD-GC/MS than by flash pyrolysis with a Curie-point pyrolyzer, permitting much easier interpretation. Ions at m/z 206, 135, and 107 were fingerprints in the characteristic mass spectra obtained by ATD-GC/MS for TOPF resin in the vulcanized rubber. 1H-Indene, styrene, and isolongifolene were observed as their characteristic mass spectra in the pyrolyzate of the rosin-modified terpene resin. From the cashew resin, phenol, 3-methylphenol, and 4-(1,1,3, 3-tetramethylbutyl)phenol were obtained as the characteristic pyrolyzates by discontinuous thermal extraction via ATD-GC/MS. Copyright 1999 John Wiley & Sons, Ltd.     

Discrimination of Thermoplastic Polyesters by MALDI-TOF MS and Py-GC/MS

The aim of this work is to discriminate thermoplastic polyester-polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polytrimethylene terephthalate (PTT), which cannot be easily identified by many methods. Both matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) and pyrolysis gas chromatography/mass spectrometry (Py-GC/MS) were applied to identify these polyesters owing to their analytical ability to determining polymers' chemical structure. The three thermoplastic polyesters can be easily distinguished by MALDI-TOF MS according to their different repeated units. Py-GC/MS was used to analyze their specific pyrolyzates. The three polyesters can be identified through their characteristic pyrolysis products as well.     

Characterisation of archaeological waterlogged wood by pyrolytic and mass spectrometric techniques

Two techniques based on analytical pyrolysis and mass spectrometry, direct exposure-MS (DE-MS) and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), were used to characterise waterlogged archaeological wood and to study degradation patterns of wood in aqueous environments. The two techniques were applied to samples from the excavation of the Site of the Ancient Ships of Pisa San Rossore in Pisa (Italy), and data were compared to those relative to native sound wood of the same species (pine, elm, beech). Both the methods result valuable in the analysis of ancient wood artefacts, avoiding the long wet-chemical procedures that are commonly used in wood analysis, and allowing us to use a minimal sample size. DE-MS achieves a global mass spectral fingerprint of lignin and polysaccharides pyrolysis compounds in few minutes, and the results have been interpreted with the support of principal component analysis (PCA) of mass spectra. Py-GC/MS permits detailed molecular analysis of pyrolysis compounds and highlights some chemical modifications of lignin in archaeological samples, as demethylation of both guaiacyl and syringyl lignin units. Both the techniques demonstrate consistent loss of polysaccharides in archaeological wood.     

Characterization and identification of acrylic binding media: influence of UV light on the ageing process

This study characterizes and identifies two different acrylic binding media such as Plextol® D498 and Primal® AC33, which are widely used in modern and contemporary art. In order to investigate their fast photooxidative deterioration when exposed to ultraviolet (UV) light, ageing studies on these materials were carried out. For this purpose, pure synthetic materials but also mixed with different inorganic pigments were identified and characterized before and after UV exposure by means of pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Particular attention was paid to the comparison of two different analytical methods: (1) single-shot method based on a pyrolysis for the analysis of polymers and (2) double-shot method, which allows a unique combination of thermal desorption for the analysis of volatile compounds and pyrolysis of the polymers themselves. These analyses have been complemented by Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR) studies. The comparison of the results obtained from unaged samples and UV-aged clearly showed material alterations as well as the formation of new products, which were recorded by FTIR-ATR. Generally, these changes were more pronounced when the acrylic binding media were mixed with pigments. The double-shot technique of Py-GC/MS additionally allowed the detection of the phenolic antioxidant in unaged Plextol® D498, but no oxidation products could be identified by Py-GC/MS in all samples.     

文物中多糖类胶结材料的热裂解-气相色谱/质谱识别

热裂解-气相色谱/质谱(Py-GC/MS)技术能够实现微量样品中有机组分的准确、快速检测,非常适用于文物中各类天然有机材料的定性分析。该研究以中国古代书画、建筑、器物等文化遗产中常用的淀粉、桃胶,以及西方文化遗产中常用的阿拉伯胶等多糖类胶结材料为研究对象,系统分析并总结各类材料的Py-GC/MS特征裂解组分及辨别方法。研究发现,淀粉、桃胶、阿拉伯胶在色谱保留时间前段的裂解产物基本一致,主要是小分子呋喃、酮类组分;在保留时间中段3类材料的裂解产物主要是呋喃型酮等组分,但不同材料的具体裂解组分差异明显;在保留时间后段,3类材料检出多种单糖衍生物以及单糖低聚体衍生物,其中桃胶与阿拉伯胶裂解组分较为接近,但与淀粉完全不同。因此,可根据不同保留时间段淀粉、桃胶、阿拉伯胶裂解产物的差异实现3类材料的辨别,其中1,6-脱水-β-D-吡喃葡萄糖只在淀粉中检出且色谱峰强度高,可以作为识别淀粉的特征组分;此外,可根据桃胶、阿拉伯胶在保留时间后段的裂解产物主要质谱碎片离子m/z 60、m/z 101的提取离子流图分布特征实现其辨别。基于所建立的Py-GC/MS方法,研究推断故宫旧藏清代剔红云龙纹天球瓶瓶口部...     

Determination of ergosterol as an indicator of fungal biomass in various samples using non-discriminating flash pyrolysis

Ergosterol is the major sterol constituent of most fungi. Since it is present in negligible amounts in higher plants, it can be used as a chemical marker for the presence of fungal contamination. A number of different ergosterol assays have been developed for the quantification of fungi in various samples. The paper presents the development of a new method for ergosterol detection based on the combination of non-discriminating flash pyrolysis with gas chromatography/mass spectrometry (Py-GC/MS). The design of the non-discriminating Py-GC/MS systems assures efficient transfer of high-molecular-weight pyrolysis products to the GC column for separation, followed by analyte detection by MS. The method was tested on different types of samples, including baker's yeast (Saccharomyces cerevisiae), moldy bread, indoor dust, and a leaf infected with powdery mildew. Ergosterol was detected in all these samples at levels ranging from approximately 4mg/g for the baker's yeast to approximately 6mug/g for household dust. The main benefits of non-discriminating pyrolysis over other techniques include elimination of the need for sample preparation, small sample size required and short analysis time.     

生物质主要组分低温热解研究

利用热重分析仪和裂解气质联用仪进行生物质主要组分低温热解特性研究。热重实验结果表明,生物质主要组分的热稳定性为：纤维素>木质素>半纤维素。半纤维素主要热解温度在210℃～320℃,而纤维素和木质素的主要热解温度分别在310℃～390℃和200℃～550℃。裂解气质联用实验考察不同温度对生物质主要组分低温热解产物的影响。半纤维素热解产物主要有乙酸、1-羟基-丙酮和1-羟基-2-丁酮,纤维素热解产物主要包括左旋葡聚糖和脱水纤维二糖,而木质素热解产物主要是邻甲氧基苯酚。     

Melanin from epidermal human melanocytes: Study by pyrolytic GC/MS

Pigmentation of human skin is determined by the presence of melanin, the polymeric pigment that is produced in melanocytes and transferred to adjacent keratinocytes. Epidermal melanocytes produce two distinct types of melanin pigments: eumelanin, composed mainly of indole-type monomers, and pheomelanin that contains benzothiazine-type backbone. Eumelanin protects skin against UV-induced damages, whereas pheomelanin is believed to act as a potent UV photosensitizer and promote carcinogenesis. In this study, pyrolysis in combination with gas chromatography and mass spectrometry (Py-GC/MS) was applied for structural studies of the epidermal pigment isolated from the cultured human melanocytes. The analysis was preceded by investigations of DOPA-originated synthetic eumelanin and pheomelanin standards. This allowed determination of pyrolytic markers for both types of melanin pigments. To obtain additional information on the natural pigment structure, the samples were thermally degraded in the presence of tetramethylammonium hydroxide as the derivatizing agent. It was shown that the analyzed pigment from normal human epidermal melanocytes derived from moderately pigmented skin is of eumelanin type with little incorporation of a pheomelanin component. The results indicate that Py-GC/MS is a rapid and efficient technique for the differentiation of epidermal melanin types and may be an alternative to commonly used methods based on chemical degradation.     

New approach for the kinetic analysis of cellulose using EGA-MS

This paper describes a new approach for kinetic analysis based on evolved gas analysis-mass spectrometry (EGA-MS) using pyrolyzer-gas chromatography/MS (Py-GC/MS). The kinetic results derived by this model-free kinetic analysis using the EGA-MS thermograms of cellulose were comparable to those using thermogravimetric analysis (TGA). The activation energies were in the range of 149–194 kJ/mol (mean 169 kJ/mol) for EGA/MS and 152–181 kJ/mol (mean 165 kJ/mol) for TGA. This suggests that Py-GC/MS can be used not only for the qualitative analysis of pyrolyzates, but also for the kinetic analysis of pyrolysis.     

Py-GC/MS, GC/MS and FTIR investigations on LATE Roman-Egyptian adhesives from opus sectile: New insights into ancient recipes and technologies

An analytical protocol based on optical microscopy, Fourier transforms infrared spectroscopy (FTIR), analytical pyrolysis in the presence of hexamethyldisilazane followed by gas chromatographic/mass spectrometric analysis (Py-GC/MS) and gas chromatography/mass spectrometry after alkaline hydrolysis, solvent extraction and trimethylsilylation (GC/MS) was used in the chemical characterisation of the original adhesives used to fix monochrome and mosaic glass and stone plaques coming from the Late Roman archaeological site of Antinoopolis (Egypt).FTIR analysis demonstrated the presence of calcite fragments, and Py-GC/MS and GC/MS analyses provided detailed molecular compositions, highlighting the presence of a wide range of compound classes including diterpenoid acids, tricyclic abietanes with a high degree of aromatisation, mid- and long-chain monocarboxylic fatty acids, mono- and di-hydroxy acids, α,ω-dicaboxylic fatty acids, n-alkanols, and n-alkanes. Characteristic biomarkers and their distribution patterns indicated the presence of pine pitch in all the adhesives, which in some cases was admixed with beeswax and brassicaceae seed oil.The results provided new insights into the complex recipes used by artisans in ancient Egypt in the production of adhesives and in the sophisticated manufacture of opus sectile decorations.     

Selective isolation of N-terminal peptides from proteins and their de novo sequencing by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry without regard to unblocking or blocking of N-terminal amino acids

We have developed a new method to determine the N-terminal amino acid sequences of proteins, regardless of whether their N-termini are modified. This method consists of the following five steps: (1) reduction, S-alkylation and guanidination for targeted proteins; (2) coupling of sulfo-NHS-SS-biotin to N(alpha)-amino groups of proteins; (3) digestion of the modified proteins by an appropriate protease followed by oxidation with performic acid; (4) specific isolation of N-terminal peptides from digests using DITC resins; (5) de novo sequence analysis of the N-terminal peptides by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) using the CAF (chemically assisted fragmentation) method or tandem mass spectrometric (MS/MS) analysis according to unblocked or blocked peptides, respectively. By employing DITC resins instead of avidin resins used in our previous method (Yamaguchi et al., Rapid Commun. Mass Spectrom. 2007; 21: 3329), it has been possible to isolate selectively N-terminal peptides from proteins regardless of modification of N-terminal amino acids. Here we propose a universal method for N-terminal sequence analysis of proteins.     

Characterisation of the transparent surface coatings on post-Byzantine icons using microscopic, mass spectrometric and spectroscopic techniques

Icons are frequently covered with superimposed transparent layers of varnish and glaze that often obscure their image and disrupt their study and conservation treatment. Using a combination of microscopic, mass spectrometric and spectroscopic techniques, a micro-analytical methodology was developed for the characterisation of these surface coatings. More specifically, light microscopy (LM), electron ionisation direct temperature resolved mass spectrometry (EI-DTMS), pyrolysis gas chromatography mass spectrometry (Py-GC/MS), imaging Fourier transform infrared spectroscopy (imaging-FTIR) and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX) were used to investigate the coatings present on the surface of five Greek post-Byzantine icons. The results showed that the aged layers of varnish and glaze contain various mixtures of materials, including diterpenoid (DTP) and triterpenoid (TTP) resins, linseed oil, lead-containing dryers, egg, and beeswax. This study also elucidated issues regarding the initial application and the later interventions on those coatings, their interaction with each other, as well as some effects observed on the underlying paint layers.     

Identifying acetylated lignin units in non-wood fibers using pyrolysis-gas chromatography/mass spectrometry

A series of non-wood plant fibers, namely kenaf, jute, sisal and abaca, have been analyzed upon pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) of the whole material. The pyrolysis products mainly arise from the carbohydrate and lignin moieties of the fibers. The lignin-derived phenols belonged to the p-hydroxyphenylpropanoid (H), guaiacylpropanoid (G) and syringylpropanoid (S) structures, and showed a high S/G ratio of between 2.0 and 5.4, the highest corresponding to kenaf. Among the lignin-derived phenols released, small amounts of sinapyl and coniferyl acetates (in both cis- and trans-forms) were identified for the first time upon Py-GC/MS of lignocellulosic materials. Acetylation of the sinapyl and coniferyl alcohols was at the gamma-position of the side chain. The release of these alcohols derived from intact acetylated lignin units upon pyrolysis seems to indicate that the native lignin in the fibers selected for this study is at least partially acetylated. Sinapyl (and coniferyl) acetates have recently been suggested to be authentic lignin precursors involved in the polymerization of lignin along with the normal sinapyl and coniferyl alcohols. Py-GC/MS will offer a convenient and rapid tool for analyzing naturally acetylated lignins, as well as to screen plant materials for the presence of acetylated units in lignin.     

Study on pyrolysis behaviors of L-tyrosine-based phthalonitrile resin

The pyrolysis behaviors of l-tyrosine-based phthalonitrile(TPN) resin were investigated by thermogravimetric-Fourier transform infrared spectrometry-mass spectrometry (TG-FTIR-MS) and Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). The small molecules produced during pyrolysis process of TPN resin were tracked in real time by TG-FTIR-MS. The larger molecules (m/z > 40) from fast pyrolysis at 900 °C of the TPN resin using Py-GC/MS were identified. From TG-FTIR-MS and Py-GC/MS results, the production pathways of pyrolysis products such as CO₂, CO, NH₃, benzonitrile and phenol were analyzed. The possible pyrolysis mechanism of TPN resin under non-oxidizing gaseous environment was proposed. The results of this study provide the useful information for designing the molecular structure of l-tyrosine-based polymers which possessing high thermal stability.     

Discrimination of genetically modified poplar clones by analytical pyrolysis–gas chromatography and principal component analysis

Analytical pyrolysis combined with gas chromatography and mass spectrometry (Py-GC–MS) is a relatively rapid (1–3 h) method for the investigation of polymers. Various wood tissues from transgenic poplar clones and from control samples have been subjected to a screening test by Py-GC–MS. Pyrolysis products from lignin- and carbohydrate-derived pyrolysis products were subjected to multivariate principal component analysis (PCA). The first three PC accounting for 39–72% of the total variance in the original data set could be attributed to vinyl products from lignin and levoglucosan from cellulose. Samples with gene construct rbcs-rol C were only discriminated by plotting PC1 versus PC3 using the whole data set. However, the wood from trees containing gene construct 35 S-rol C were discriminated in all examined models indicating significant impacts during biosynthesis of the wood. One sample within the data set was further clustered because it turned out that this tree died off after two vegetation periods.     

Flame retardant epoxy resins based on diglycidyl ether of (2,5-dihydroxyphenyl)diphenyl phosphine oxide

Phosphine oxide-containing epoxy resins were prepared from diglycidyl ether of (2,5-dihydroxyphenyl)diphenyl phosphine oxide and diglycidyl ether of bisphenol A by crosslinking with 4,4′-diaminodiphenylmethane. Several (2,5-dihydroxyphenyl)diphenyl phosphine oxide/diglycidyl ether of bisphenol A molar ratios were used to obtain materials with different phosphorus content. The properties of the thermosetting materials were evaluated by differential scanning calorimetry, dynamic mechanical analysis, thermogravimetric analysis, and limiting oxygen index and related to the phosphorus content. Thermal and thermooxidative degradation was studied by GC/MS, ³¹P MAS NMR spectroscopy, and scanning electron microscopy. Limiting oxygen index values indicate good flame retardant properties that are related to the formation of a protective phosphorus-rich layer that slowed down the degradation and prevented it from being total. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2142–2151, 2007     

热裂解气相色谱质谱法分析聚合物中红磷

采用单击热裂解(PY)模式和逸出气体分析(EGA)程序升温两种热裂解模式对红磷样品进行定性分析,利用气相色谱分离技术对红磷进行分离,根据红磷的特征质谱31,62,93,124及特征丰度比,质谱法分析不同材料中的红磷含量。单击热裂解模式下,材质和添加剂有可能对红磷造成干扰,改进后的EGA热裂解模式能排除红磷检测中材质和添加剂的干扰,并采用改进后的EGA裂解程序测定自制阳性样品中红磷的含量。结果表明:通过优化裂解温度和气相色谱条件可以有效改善红磷的分析结果,红磷质量浓度在100~500 mg/kg范围内具有良好线性,加标回收率在90.7%~97.7%,相对标准偏差(RSD)为1.6%~2.3%,定量限为81.27 mg/kg。     

Pyrolysis-GC/MS and TG/MS study of mediated laccase biodelignification of Eucalyptus globulus kraft pulp

Biobleaching studies using laccase mediator system (LMS) were carried out, under optimized conditions, on two unbleached Eucalyptus globulus kraft pulps, one produced by conventional way, with kappa number of 16.1, and another with kappa number of 14.5, obtained by modified kraft procedure with a high liquor/wood ratio and with black liquor replacement in the middle of the cooking. The pulp properties before and after LMS and alkaline extraction were evaluated in terms of kappa number, hexeneuronic acid content, viscosity, brightness and acid insoluble lignin content.The original milled wood sample and the kraft pulps were characterized by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and thermogravimetry/mass spectrometry (TG/MS). Eucalypt wood lignin produces guaiacol and syringol derivatives during pyrolysis. These lignin products can be detected with high sensitivity using the selected ion chromatograms even in the bleached pulp of low lignin content (about 0.5%). Py-GC/MS revealed that the lignin moieties were similarly altered during biobleaching as during pulping, which is exemplified by the preferential removal of aldehyde groups from the alkyl side groups. Semi-quantitative analysis of the pyrograms indicates that the lignin content of the biobleached pulps is reduced by about half in comparison with the unbleached pulps. The TG/MS results show that the hemicellulose content of wood was strongly modified during pulping resulting in higher thermal stability.     

Mass spectrometric techniques for characterizing low-molecular-weight resins used as paint varnishes

The molecular structure of three low-molecular-weight resins used as paint varnishes has been characterized by use of an approach based on three different mass spectrometric techniques. We investigated the ketone resin MS2A, the aldehyde resin Laropal A81, and the hydrocarbon resin Regalrez 1094, now commonly used in restoration. To date, the molecular structures of these resins have not been completely elucidated. To improve current knowledge of the chemical composition of these materials, information obtained by gas chromatography–mass spectrometry (GC/MS), pyrolysis–gas chromatography–mass spectrometry (Py/GC/MS), and electrospray ionization mass spectrometry (ESI–Q–ToF) was combined. Analysis, in solution, of the whole polymeric fraction of the resins by flow-injection ESI–Q–ToF, and of the non-polymeric fraction by GC–MS, enabled us to identify previously unreported features of the polymer structures. In addition, the Py–GC/MS profiles that we obtained will help to enhance the databases currently available in the literature. The proposed approach can be extended to other low-molecular-weight resins used as varnishes in conservation.     

Comparison of metal and metal oxide media for phosphopeptide enrichment prior to mass spectrometric analyses

Several affinity resins consisting of ionic metals or metal oxides were investigated for their phosphopeptide enrichment capabilities with subsequent mass spectrometric analyses. Commercially-available enrichment metal oxide affinity chromatography (MOAC) resins using manufacturer’s and/or published protocols were compared and evaluated for the most efficient and selective method that could be implemented as a standard enrichment procedure. From these comparative analyses, using a tryptic digest of casein proteins, it was determined that in our hands, two of the resins out-performed the others based on a variety of criteria, including the number of phosphorylation sites identified during MS analyses, the lower numbers of nonspecifically bound peptides observed, and the limits of detection. Applicability of these enrichment resins to a complex biological mixture was investigated. For this work, a mixture of avian histones was digested, subjected to titanium dioxide phosphopeptide enrichment, and analyzed by mass spectrometry. Eight phosphorylated tryptic peptides were observed following enrichment and subsequent LC/MS/MS analyses. Of note, seven of the eight phosphopeptides were not observed without titanium dioxide enrichment. From these analyses, four sites of phosphorylation were unequivocally determined, two of which have not been reported previously. Four additional phosphopeptides were observed; however, the site of phosphorylation could not be distinguished but was localized to one of two possible amino acids. These methods should aid in the investigation of proteins post-translationally modified with phosphate, especially those present at low concentrations as was demonstrated by successful enrichment at the femtomole level.