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.     

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.     

Analysis of an egyptian mummy resin by mass spectrometry

Fast atom bombardment combined with mass spectrometry (FAB/MS), high resolution FAB/MS, FAB tandem mass spectrometry (MS/MS), and gas chromatography/mass spectrometry (GC/MS) were used to determine the composition of the resinous material recovered from the wrappings of an Egyptian mummy believed to be from the Roman period (100–350 A.D.). FAB/MS and MS/MS studies identified several oxidation products of abietic acid as the principal resin components, indicating that one or more species of coniferous trees were used by the Egyptians as a source of the resin. GC/MS studies also identified several n-alkanes with carbon numbers from C₁₉ to C₃₃ in the sample. The relative amounts of these n-alkanes, along with characteristic trace metals, indicate that bitumen, an asphalt native to the region, was added to the resin. The presence of this ancient source of carbon in this sample explains the inconsistent date assigned to the mummy by carbon-14 analysis.     

MALDI-TOF mass spectrometry on cellulosic surfaces of fresh and photo-aged di- and triterpenoid varnish resins

Matrix-Assisted Laser Desorption/Ionization Time-of-Flight mass spectrometry (MALDI-TOF-MS) on cellulosic surfaces is shown to be a suitable method for examining highly oxidized terpenoids, which are otherwise too difficult to determine by other techniques. By crystallization of a 2,5-dihydroxybenzoic acid (DHB) matrix and the sample solution on cellulose-coated thin layer chromatography(TLC) plates, spectra with good signal/noise ratios are obtained and no significant interferences due to matrix ions or cluster ions were produced, at least not in the range of m/z values of interest (>300 Da). The validity of the method was tested on natural di- and triterpenoid resins used as paint varnishes by Old Masters. The samples were analyzed before and after artificial light ageing. Di- and triterpenoid compounds, being very sensitive towards photo-oxidation, were found as oxidized molecules even in the raw resins and in the unexposed varnish layers. Artificial ageing simulating window-filtered daylight resulted in a stronger oxidation of the original terpenoids and the incorporation of up to six oxygen atoms per molecule could be demonstrated. Terpenoid dimers and their oxidation products were also detected.     

Study of the microbiodegradation of terpenoid resin-based varnishes from easel painting using pyrolysis–gas chromatography–mass spectrometry and gas chromatography–mass spectrometry

The alterations produced by microbiological attack on terpenoid resin-based varnishes from panel and canvas paintings have been evaluated using pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS) and gas chromatography–mass spectrometry (GC–MS). The proposed methods include the on-line derivatisation of drying oils and diterpenoid resins using hexamethyldisilazane during pyrolysis and the application of methyl chloroformate as a derivatisation reagent for triterpenoid resins in GC–MS. Two types of specimens, consisting of model oil medium prepared from linseed oil and model spirit varnishes prepared from colophony and mastic resins dissolved in turpentine, have been used as reference materials. For a series of specimens upon which different genera of bacteria and fungi were inoculated and encouraged to grow, analyses indicated that no mechanisms that commonly occur during the attack of enzymes on drying oils and terpenoid biodegraders were observed to occur in the oil medium and varnishes studied. Thus, the degradation pathways observed in the performed trials usually occur as consequence of natural ageing. Specific trials consisting of the application of biocides to uninoculated colophony varnish resulted in the identification of processes that produce undesirable degradation of the varnish due to interactions between the biocide and the varnish components. Finally, the studied biocides—Biotin, New-Des and Nipagine—generally exhibited good inhibiting effects on the microorganisms studied, although some interesting differences were found between them regarding the application method and type of biocide.     

Identification of non-cross-linked compounds in methanolic extracts of cured and aged linseed oil-based paint films using gas chromatography-mass spectrometry

Methanolic extracts of paint samples of different composition and age were qualitatively investigated by GC–MS using an on-column injector after off-line methylation or trimethylsilyl derivatisation, and on-line thermally assisted (trans)methylation with tetramethylammonium hydroxide using Curie-point pyrolysis–GC–MS. The combination of these three analytical strategies led to the identification of typical oxidation products of unsaturated fatty acids by interpretation of their mass spectrum. Some of the identified compounds have not been reported before. Both the off-line and on-line GC–MS strategy show series of short-chain fatty (di)acids and C₁₆ and (oxidised) C₁₈ fatty acids. The major advantage of the on-line pyrolysis–GC–MS approach is that chemical work-up is minimal and very quick. With this technique both the carboxylic acid functionalities, and hydroxyl groups are methylated. Young paint films are shown to contain relatively more oxidised C₁₈ fatty acids and less diacids compared to older paints, which is indicative for the on-going oxidation processes within the paint. After trimethylsilylation, monoacylglycerols are detected indicative for hydrolytic processes, which reflect the relative distribution of the most prominent silylated fatty acids present. Relatively more C₁₆ and C₁₈ monoacylglycerols are found in young paints, whereas older paints contain higher amounts of monoacylglycerols of diacids.     

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.     

Lipid Peroxidation in Algae Oil: Antagonist Effects of Natural Antioxidants

Tandem mass spectrometry is proposed to check lipid oxidation, a free radical-mediated phenomenon which effects oxidative deterioration in polyunsaturated fatty acids. Antioxidants are used by the food industry to delay the oxidation process. This process can be controlled by antioxidants, which may occur as natural constituents of foods or may be intentionally added to products. Synthetic antioxidants such as BHT, BHA, and propyl gallate have been extensively used as antioxidants in the industry. The worldwide tendency to avoid or minimize the use of synthetic food additives has prompted the replacement of synthetic antioxidants with natural analogues. The entire process can be supported by the detection and characterization of the reacting species by suitable application of electrospray tandem mass spectrometry under collision-induced dissociation (ESI-CID-MS/MS). Natural antioxidants were tested in this study to check the oxidative stability of algae oil when adding the natural additive. Results were observed in algae oil in situ using electrospray mass spectrometry in tandem with collision-induced dissociation tandem mass spectrometry (ESI-CID-MS/MS) and the POBN spin trapper. The results indicate that alpha-tocopherol is a better antioxidant.     

压力对塔里木原油四组分热解性能的影响

压力对深层油藏原油热化学过程的影响尚存在较大争议,为研究其在油藏原油热解成气过程中的作用机理,我们在450℃、5~40 MPa压力下对塔里木原油四组分(饱和分、芳香分、胶质和沥青质)进行了封闭体系的热解实验,通过气相色谱(GC)和气相色谱/质谱(GC/MS)分别对原油四组分热解反应的气体产物及饱和分热解过程的液态产物进行了分析。结果表明,在450℃、24 h及不同压力下,沥青质热解产气率高于胶质、芳香分和饱和分;四组分的气相热解产物中,C1的产率明显高于C2~C5组分。增大压力抑制沥青质、胶质及芳香分的热解产气过程而促进饱和分的热解产气过程。随压力的增大,饱和分热解的液态产物的主峰组分碳数先减小,再增大。压力低于20 MPa时,饱和分热解过程中以裂解反应为主;高于30 MPa时,增大压力有利于缩合反应。研究结果可为认识深层油藏原油的稳定程度及天然气的成因提供一定的理论参考。     

Characterisation of organic residues in pottery vessels of the Roman age from Antinoe (Egypt)

In the framework of a study on the Egyptian ceramic vessels belonging to the archaeological collection of the Istituto Papirologico Vitelli (Florence), the characterisation of organic residues from three findings of the 5th–7th centuries A.D. has been performed. The materials were identified by two analytical procedures based on Fourier transformed infrared spectroscopy (FTIR) and on gas chromatography coupled with mass spectrometry (GC–MS), respectively. The first procedure is suitable for detecting the functional groups of organic substances and thus for distinguishing them; the second permits the simultaneous analysis of several natural substances such as vegetable resins and oils, bitumen, tar and pitch, and waxes.The presence of monocarboxylic acids, α,ω-dicarboxylic acids, long-chain dihydroxylated acids, and terpenic species, highlights that although the organic residues showed a high heterogeneity in composition, they mainly consisted of materials of vegetable origin. In particular, the presence of oxidation products of characteristic unsaturated fatty acids suggests the occurrence of oil produced from plant seeds of the Cruciferae family, some of which are reported to have been used in ancient Egypt to produce oil. Moreover, the presence of characteristic diterpenic biomarkers in two of the three pieces of pottery enables us to assess the use of both pine resin and pine pitch.     

Effect of Natural Antioxidants from Marigolds (Tagetes erecta L.) on the Oxidative Stability of Soybean Oil

In recent years, synthetic antioxidants that are widely used in foods have been shown to cause detrimental health effects, and there has been growing interest in antioxidants realised from natural plant extracts. In this study, we investigate the potential effects of natural antioxidant components extracted from the forage plant marigold on the oxidative stability of soybean oil. First, HPLC-Q-TOF-MS/MS was used with 1,1-diphenyl-2-picrylhydrazyl (DPPH) to screen and identify potential antioxidant components in marigold. Four main antioxidant components were identified, including quercetagetin-7-O-glucoside (1), quercetagetin (2), quercetin (3) and patuletin (4). Among them, quercetagetin (QG) exhibited the highest content and the strongest DPPH radical scavenging activity and effectively inhibited the production of oxidation products in soybean oil during accelerated oxidation, as indicated by reductions in the peroxide value (PV) and acid value (AV). Then, the fatty acids and volatile compounds of soybean oil were determined with gas chromatography–mass spectrometry (GC-MS) and headspace solid-phase microextraction–gas chromatography–mass spectrometry (HS-SPME-GC-MS). A total of 108 volatile components, including 16 alcohols, 23 aldehydes, 25 ketones, 4 acids, 15 esters, 18 hydrocarbons, and 7 other compounds, were identified. QG significantly reduced the content and number of aldehydes and ketones, whereas the formation of acids and hydrocarbons was completely prevented. In addition, the fatty acid analysis demonstrated that QG significantly inhibited oxidation of unsaturated fatty acids. Consequently, QG was identified as a potential, new natural antioxidant that is believed to be safe, effective and economical, and it may have potential for use in plant extracts feed additives.     

Analysis of triglycerides in food items by desorption electrospray ionization mass spectrometry

The triglyceride composition and oxidation behavior of edible oil and margarine samples were analyzed by desorption electrospray ionization mass spectrometry (DESI‐MS). For the characterization of the lipids, the chain length and the degree of unsaturation of the fatty acids were determined. The measurements were carried out in positive ion mode; the triglycerides were detected as alkali metal or ammonium adducts. The DESI solvent was water/methanol 1:1 (v/v); measurements were carried out both with and without the addition, as an ionizing agent, of ammonium acetate that enhances the signal intensity of the ammonium adduct ions. The spectra were interpreted for both cases and intensities were compared. Triglyceride monomers and dimers were observed in the spectra. Tandem mass spectrometric (MS/MS) measurements were carried out to determine the structure of the triglycerides. It was demonstrated that the terminal fatty acids in the sn1‐ or sn3‐position are more likely to be cleaved than the internal fatty acid (sn2‐position). Characteristic triglyceride patterns were obtained using a simple and rapid sample preparation protocol comprising the simple deposition of samples onto a glass carrier surface. The triglyceride data was analyzed by principal component analysis (PCA). The different edible oils were clearly separated and the hydrogenated derivatives were identified by their triglyceride spectra. The oxidation of the oil samples was observed and the oxidation products were detected and identified. This method provides a fast and simple technique for the detection and analysis of triglycerides in oil‐ or fat‐containing samples ranging from food items to tissue samples. The potential application areas include nutritional studies, the food industry and cosmetics. Copyright © 2010 John Wiley & Sons, Ltd.     

松脂的催化歧化反应产物的气相色谱-质谱分析

采用气相色谱-质谱技术对松脂的催化歧化新工艺的反应产物进行分析,共分离出45个峰,鉴定出其中的38个化合物,并发现松脂歧化产物中歧化松节油的主要成分为对伞花烃,含量为16.26%;歧化松香的主要成分为脱氢枞酸和氢化树脂酸,其含量分别为41.58%和21.43%。在此基础上对松脂歧化反应过程进行了初步探讨,认为松脂原料中的酸性物质发生分子间氢转移反应,萜烯烃的存在促进了脱氢反应的进行;在树脂酸提供的酸性环境下松脂原料中中性油的主要成分双环单萜烯发生开环异构形成单环单萜烯,单环单萜烯再进行催化脱氢转化为对伞花烃。分析结果表明,直接以松脂为原料进行催化歧化反应可同时获得特级歧化松香和高含量的对伞花烃。     

Characterisation of varnishes used in violins by pyrolysis-gas chromatography/mass spectrometry

The correct characterisation and a detailed knowledge of the materials originally used in violin varnishes, like natural resins, is crucial for the conservation in museums and for a suitable restoration technique. The study presented here reports on the potential of pyrolysis (Py) coupled with gas chromatography (GC) and mass spectrometry (MS) for the identification of chemical markers of each resin; this technique is very sensitive and selective, it needs a small quantity of sample and does not require chemical treatments. To improve the chromatographic behaviour of polar compounds the derivatising agent tetramethylammonium hydroxide (TMAH) in combination with pyrolysis has been used, in the so-called TMAH thermochemolysis or thermally assisted hydrolysis and methylation (THM), or more simply pyrolysis-methylation. The natural resins studied were colophony, sandarac, manila copal, elemi, amber and benzoin, mainly composed of terpenic compounds, with the exception of the latter, composed of aromatic compounds. Many compounds were identified; in particular, methyl esters of resinous acids that, individually or in a group, can be used as chemical markers. However, through this technique it was not possible to distinguish between the sandarac and manila copal resins because their chromatographic behaviour is very similar. Finally, the procedure applied has been employed in the characterisation of original varnish samples.     

Analysis of diterpenoic compounds in natural resins applied as binders in museum objects by capillary electrophoresis

The exudates of conifers consist mainly of diterpenoic acids of the abietane and pimarane type (abietic, neoabietic, dehydroabietic, palustric, pimaric, isopimaric, levopimaric and sandaracopimaric acid) and larixol acetate. These natural resins were used as adhesives, coatings, varnishes or plasticizers in artistic and historic works since ancient times. For the purpose of conservation and restoration and for art historic examination of such museum objects the identification of the binding media used is undoubtedly of paramount importance. In the present paper, the characterization of these resins based on the pattern of their diterpenoid constituents is carried out by capillary electrophoresis. For separation a background electrolyte which has been initially introduced for the analysis of chlorinated and natural resin acids in waste water was modified and the experimental conditions were adjusted in terms of resolution and analysis time. Separation was carried out in borate buffer at pH 9.25 (ionic strength 20 mmol L(-1)) with methyl-beta-cyclodextrin and sulfobutylether-beta-cyclodextrin as additives to increase selectivity and enhance the solubility of the analytes. With this electrophoretic system the resin acids of interest and larixol acetate--all as anionic cyclodextrin complexes--were separated within 5 min and detected at 200, 250 and 270 nm with a diode array detector. The electrophoretic patterns served for the characterisation of the relevant diterpenoic resins, balsams and copals. Sample pre-treatment was limited to sonication in methanol at 55 degrees C for 30 min. This enables the identification of the resins in mixtures with other binders like plant gums, animal glues or drying oils, even when these media are present in excess. Colophony was identified as resinous constituent of a modelling mass for gilded frames originating from the 19th century.     

Application of microemulsions for the removal of synthetic resins from paintings on canvas

Abstract

Traditional cleaning methods with organic solvents often are not suitable for removal of aged resin so researchers have to find new formulations. In this work, a case study is reported in which new microemulsions were applied on the surface of a painting covered by some aged resin layers used during a previous restoration. Based on the quality of the intervention and the analysis of a sample of the varnish carried out with both MALDI-TOF and ATR-IR spectrometers, it was conjectured that this undesired material could be an acrylic polymer. So it was chosen to use xylene, ethyl acetate and propylene carbonate (XYL and EAPC) microemulsions (O/W oil in water). The first is able to solubilise only acrylic polymers, the second may solve both acrylic and vinyl resins. The first has had the greatest effect allowing complete varnish removal and original artwork restoration.     

超高效液相色谱-串联质谱法同时测定鱼制品中残留的7种性激素

以电喷雾离子源(ESI)为电离源,在正离子采集模式下建立了鱼制品中7种性激素（甲基炔诺酮、甲基睾酮、丙酸睾酮、醋酸甲羟孕酮、醋酸甲地孕酮、醋酸氯地孕酮、诺龙）的超高效液相色谱-质谱/质谱(UPLC-MS/MS)检测方法。样品被酶解后用甲醇提取,提取液经氯化锌(ZnCl2)去脂、LC-C18和LC-NH2固相萃取柱净化、Waters ACQUITYTM UPLC BEH-C18色谱柱(100 mm×2.1 mm, 1.7 μm)分离,在多反应监测模式下进行UPLC-MS/MS分析。7种性激素的方法检出限(S/N=3)为0.08～0.17 μg/kg,定量限(S/N=10)为0.24～0.58 μg/kg。考察了内标法和基质匹配外标法对7种性激素进行定量的回收率与精密度: 添加水平为1, 4 μg/kg时,以内标法定量,7种性激素的平均回收率为76%～118%,相对标准偏差（RSD）为5.0%～11.3%;以基质匹配外标法定量,7种性激素的平均回收率为66%～94%,RSD为4.5%～10.7%。该结果表明两种方法均能够满足鱼制品中7种性激素的多残留检测要求。应用建立的方法对市售脱脂大黄鱼及烤鱼片进行检测,未发现7种目标违禁性激素。     

Curie-point pyrolysis gas chromatography/mass spectrometry in the identification of paint media

Curie-point pyrolysis gas chromatography/mass spectrometry has been applied to different model paint samples containing proteinaceous (egg yolk) and oily (linseed oil) media. Results of pyrolysis at 610°C are highly reproducible, and among the different pyrolysis products some compounds diagnostic for the different binders have been identified. The application of the method to real samples, i.e. from the oil painting ‘Ritratto’ by Giuseppe Nogari (1669–1763) and from the tempera paint on the ligneous roof of S. Giobbe church (16th century) in Venice, proves its effectiveness in the identification of binding media.     

Hyphenation of Curie-point-pyrolysis high-resolution gas chromatography with several spectroscopic methods for the analysis of cured epoxy resins

The coupling of Curie-point pyrolysis (Py) with gas chromatography (GC) and mass spectrometry (MS) or Fourier transform infrared spectroscopy (FTIR) has been widely reported. The approach reported in this paper combines chromatographic separation with eluent monitoring by use of three different spectroscopic detectors (MS, FTIR and Atomic Emission Detector [AED]). The features of these detectors, with different selectivities, are shown for the analysis of cured epoxy resins. Besides characterisation of major resin constituents by identification of the pyrolysis products, the usefulness of the AED is also revealed by the detection of minor compounds (such as coupling agents) in cured epoxy resins.     

Quantitative GC–MS Analysis of Artificially Aged Paints with Variable Pigment and Linseed Oil Ratios

In this study, quantitative gas chromatography–mass spectrometry (GC–MS) analysis was used to evaluate the influence of pigment concentration on the drying of oil paints. Seven sets of artificially aged self-made paints with different pigments (yellow ochre, red ochre, natural cinnabar, zinc white, Prussian blue, chrome oxide green, hematite + kaolinite) and linseed oil mixtures were analysed. In the pigment + linseed oil mixtures, linseed oil concentration varied in the range of 10 to 95 g/100 g. The results demonstrate that the commonly used palmitic acid to stearic acid ratio (P/S) to distinguish between drying oils varied in a vast range (from especially low 0.6 to a common 1.6) even though the paints contained the same linseed oil. Therefore, the P/S ratio is an unreliable parameter, and other criteria should be included for confirmation. The pigment concentration had a substantial effect on the values used to characterise the degree of drying (azelaic acid to palmitic acid ratio (A/P) and the relative content of dicarboxylic acids (∑D)). The absolute quantification showed that almost all oil paint mock-ups were influenced by pigment concentration. Therefore, pigment concentration needs to be considered as another factor when characterising oil-based paint samples based on the lipid profile.