Oxidative degradation products analysis of polymer materials by pyrolysis gas chromatography–mass spectrometry

Pyrolysis gas chromatography–mass spectroscopy (PGC–MS) has been proved to be a powerful method to analyze both the volatile additives and the macromolecular structure of polymer materials. In this paper, flash evaporation technique was used to analyze the volatile degradation products of polymer materials during natural and artificial aging. In high density polyethylene (HDPE) composites, mainly n-alkanes with carbon number from 14 to 29 were detected after natural aging, while no oxidative product was found. Different composites have different n-alkane distributions. In contrast, various oxidative products including ketones, alcohols, esters and unsaturated species could be found in aged polypropylene (PP) nanocomposites. Nanoparticles accelerated the chain scission of PP and increased the formation of oxidative products significantly. During thermal oxidation of nitrile rubber (NBR) seal rubbers, heat/oxidation-induced extra crosslinking predominated and no volatile degradation products was detected. The main change happened in the volatiles is the decrease of additives, especially paraffins, antioxidant RD and hindered phenol. This resulted in the hardening of the rubber and the weakening of the protection from oxidation. Furthermore, the additive distribution along the depth was investigated, showing different migration speeds of different additives. From the additive levels remained in the NBR rubber, it is possible to predict the degradation status. In summary, PGC–MS can supply abundant information of polymer degradation and is helpful for mechanism research.     

Identification of monoacylglycerol regio-isomers by gas chromatography–mass spectrometry

Monoacylglycerols (MAGs) are lipids found in trace amounts in plants and animal tissues. While they are widely used in various industrial applications, accurate determination of the regio-specific distribution is hindered by the lack of stable, commercially available standards. Indeed, unsaturated β-MAG (or Sn-2 MAG) readily undergoes isomerization into α-MAG (acyl chain is attached to the Sn-1 or the Sn-3 position). In the present study, we describe structural elucidation of α- and β-regio-isomers of monopalmitoyl-glycerol (MAG C16:0) as model compounds in their silylated forms using gas chromatography–mass spectrometry (GC–MS) with electronic impact (EI) ionization. MS fragmentation of α-MAG C16:0 is characterized by the loss of methylene(trimethylsilyl)oxonium (103 amu) and the consecutive loss of acyl chain yielding a fragment ion at m/z 205. The fragmentation pattern of β-MAG C16:0 shows a series of diagnostic fragments at m/z 218, 203, 191 and 103 that are not formed from the α-isomer and hereby enable reliable distinction of these regio-isomers. Possible fragmentation scenarios are postulated to explain the formation of these marker ions, which were also applied to characterize the regio-isomer composition of a complex mixture of MAG sample containing n-3 long-chain polyunsaturated fatty acids.     

Characterisation of permanent markers by pyrolysis gas chromatography–mass spectrometry

Pyrolysis gas chromatography–mass spectrometry (PyGC-MS) was used as a rapid method for the characterization of permanent marker ink. Twenty-four samples of various colours purchased from different manufacturers were characterised. Four main typologies of polymer-binding medium could be distinguished on the basis of the pyrolysis products, and differentiation between permanent markers of different manufacturers could be accomplished. For some permanent marker samples, PyGC-MS analysis allowed pigment identification as well.     

Identification of polyethanolamines by chromatography–mass spectrometry

Presumable structures of polyethanolamines, synthesized by the catalytic β-hydroxyethylation of ammonia with an excess of ethylene oxide are determined by gas chromatography–electron ionization mass spectrometry and tandem mass spectrometry qualitatively, following fragmentation ways and also taking into account retention data. The preferable paths of consecutive reactions of the synthesis of polyethanolamines in a homologous series of isomers are found.     

Determination of diketopiperazines of Burkholderia cepacia CF-66 by gas chromatography–mass spectrometry

Bacteria communicate with each other by a process termed “quorum sensing” (QS), and diffusible, low-molecular-weight chemicals, called signal molecules, are used as the communication languages. In cell-free Burkholderia cepacia CF-66 culture supernatants, five compounds suspected of being signal molecules were identified. The gene (cepI) related with AHLs synthesis were not detected by polymerase chain reaction (PCR) using specific primers. Gas chromatography–mass spectrometry (GC–MS) revealed that these compounds were not AHLs but the diketopiperazines (DKPs) cyclo(Pro–Phe), cyclo(Pro–Tyr), cyclo(Ala–Val), cyclo(Pro–Leu), and cyclo(Pro–Val), all of which were both d and l-type. Four kinds of DKPs had been isolated from other Gram-negative bacteria, but the other was a novel kind discovered in CF-66, and l-cyclo (Pro–Phe) was quantified by GC–MS. It was found that exogenous DKPs had a negative effect on the candidacidal activity of the culture supernatant extracts.     

Analytical determination of nicotine in tobacco leaves by gas chromatography–mass spectrometry

A preliminary investigation using gas chromatography–mass spectrometry (GC–MS) to analyze the nicotine contained in tobacco leaves was carried out. Nicotine is an alkaloid and tobacco leaves was extracted with methanol and determined by GC–MS. The detection limit for nicotine was at the ppm level for non selective monitoring and the nanogram level for selective detection. This is a simple chromatography–mass spectrometry method for the analysis of nicotine in tobacco leave. Compared to other currently utilized methods for the detection of nicotine in tobacco leaves, the GC–MS provided advantages of high sensitivity, nicotine specific detection and lower instrumentation cost.     

Analysis of chemical profiles of insect adhesion secretions by gas chromatography–mass spectrometry

This article reports on the chemical analysis of molecular profiles of tarsal secretions of the desert locust Schistocerca gregaria (Forsskål, 1775) by gas chromatography hyphenated with quadrupol mass spectrometry (GC–MS) as well as ¹H-nuclear magnetic resonance (¹H NMR) spectroscopy. Special focus of this study was to elaborate on sampling methods which enable selective microscale extraction of insect secretions in a spatially controlled manner, in particular tarsal adhesive secretions and secretions located on cuticle surfaces at the tibia. Various solvent sampling procedures and contact solid-phase microextraction (SPME) methods were compared in terms of comprehensiveness and extraction efficiencies as measured by signal intensities in GC–MS. Solvent sampling with water as extraction solvent gave access to the elucidation of chemical profiles of polar compound classes such as amino acids and carbohydrates, but is extremely tedious. Contact SPME on the other hand can be regarded as a simplified and more elegant alternative, in particular for the lipophilic compound fraction. Many proteinogenic amino acids and ornithine as well as carbohydrate monomers arabinose, xylose, glucose, and galactose were detected in tarsal secretions after acid hydrolysis of aqueous extracts. Qualitatively similar but quantitatively significantly different molecular profiles were found for the lipid fraction which contained mainly n-alkanes and internally branched monomethyl-, dimethyl-, and trimethyl-alkanes in the C23–C49 range as well as long chain fatty acids and aldehydes. Especially, hydrocarbons with >C40 carbon numbers have previously been rarely reported for insect secretions. The results suggest that the investigated insect secretions are complex emulsions which allow the attachment of tarsi on various otherwise incompatible materials of smooth and rough surfaces. The solid consistence of the established alkanes at ambient temperatures might contribute to a semi-solid consistence of the adhesive, amalgamating partly opposing functions such as slip resistance, tarsal release, desiccation resistance, and mechanical compliance. The methods developed can be extended to other similar applications of studying compositions of insect secretions of other species.     

Carbohydrate analysis of hemicelluloses by gas chromatography–mass spectrometry of acetylated methyl glycosides

A method based on gas chromatography-mass spectrometry analysis of acetylated methyl glycosides was developed in order to analyze monosaccharides obtained from various hemicelluloses. The derivatives of monosaccharide standards, arabinose, glucose, and xylose were studied in detail and (13)C-labeled analogues were used for identification and quantitative analysis. Excellent chromatographic separation of the monosaccharide derivatives was found and identification of the anomeric configuration was feasible through a prepared and identified pure methyl 2,3,4,6-tetra-O-acetyl-β-D-glucopyranoside. The electron ionization mass spectrum and fragmentation path was studied for each monosaccharide derivative. Fragment ion pairs of labeled and unlabeled monosaccharides were used for quantification; m/z 243/248 for glucose, 128/132 for xylose, and 217/218 for arabinose. Using the intensity ratios obtained from the extracted ion chromatograms, accurate quantification of monosaccharide constituents of selected hemicelluloses was demonstrated.     

Characterization of O-trimethylsilyl oximes of trisaccharides by gas chromatography–mass spectrometry

Gas chromatography (GC) data (linear retention indices and relative areas) and mass spectra (most representative m/z fragments) of 12 reducing trisaccharides as trimethylsilyl oximes (TMSO) and four non-reducing as trimethylsilyl (TMS) ethers have been described for the first time and related to their structural features. Some trends have been observed: earlier elution of non-reducing compounds and fructotrioses; aldotrioses bearing the reducing end with link in position 6 showing the highest retention. Abundance of several fragment ions and their ratios were useful for trisaccharide characterization; some of these features seem to be useful for the characterization of new trisaccharides.     

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.     

Study of archaeological artifact by chromatography–mass spectrometry

An archaeological artifact, representing a compound piece of the Bronze Age, the outer surface of which is encrusted with seeds, has been investigated. The chemical composition of the organic binder was determined by gas chromatography and mass spectrometry; X-ray fluorescence analysis was used to determine the nature of the inorganic base of the artifact.     

Rapid comprehensive characterization of crude oils by thermogravimetry coupled to fast modulated gas chromatography–single photon ionization time-of-flight mass spectrometry

Comprehensive multi-dimensional hyphenation of a thermogravimetry device (i.e. a thermobalance) to gas chromatography and single photon ionization–time-of-flight mass spectrometry (TG–GC×SPI–MS) has been used to investigate two crude oil samples of different geographical origin. The source of the applied vacuum ultraviolet radiation is an electron beam pumped rare gas excimer lamp (EBEL). The soft photoionization favors the formation of molecular ions. Introduction of a fast, rapidly modulated gas chromatographic separation step in comparison with solely TG–SPI–MS enables strongly enhanced detection especially with such highly complex organic matrices as crude oil. In contrast with former TG–SPI–MS measurements, separation and identification of overlying substances is possible because of different GC retention times. The specific contribution of isobaric compounds to one mass signal is determined for alkanes, naphthalenes, alkylated benzenes, and other compounds.

Neurosteroid analysis by gas chromatography–atmospheric pressure photoionization–tandem mass spectrometry

A new and simple APPI interface employing commercially available hardware is used to combine GC to MS. The feasibility of the method is demonstrated in the analysis of urine samples for neurosteroids as their trimethylsilyl (TMS) derivatives. The effect of different dopants (chlorobenzene, toluene, anisole) on the ionization of the TMS derivatives was investigated. With chlorobenzene, the TMS derivatives produced intense molecular ions with minimal fragmentation, and chlorobenzene was selected as best dopant. Protonated molecules in addition to intense molecular ions were produced with toluene and anisole. The performance of the method was verified in the analysis of human urine samples. Chromatographic performance was good with peak half-widths of 3.6–4.3 s, linearity (r² > 0.990) was acceptable, limits of detection (LODs) were in the range of 0.01–10 ng mL⁻¹, and repeatability was good with relative standard deviations (rsd%) below 22%. The results show that the method is well suited for the determination of neurosteroids in biological samples.     

Determination of elemental sulfur in coal by gas chromatography – mass spectrometry

A method for the determination of S⁰ in coal based on the extraction with cyclohexane with subsequent quantitative analysis of elemental sulfur in the extract by GC/MS is described. The quantity of elemental sulfur was determined in four coal samples with different distribution of sulfur forms. The effect of solvent and extraction time on the efficiency of sulfur removal was studied. The elemental sulfur extracted from coal occurred in the form of S₆, S₇ and S₈. Calibration solutions were prepared from freshly recrystalized elemental sulfur. It was found that the injection temperature has a crucial influence on the m/z 64 ion chromatogram.     

Determination of petitgrain oils landmark parameters by using gas chromatography–combustion–isotope ratio mass spectrometry and enantioselective multidimensional gas chromatography

Gas chromatography–combustion–isotope mass spectrometry was employed for the assessment of the Carbon isotope ratios of volatiles in Italian mandarin and lemon petitgrain oils. In addition, the composition of the whole oil and the enantiomeric distribution of selected chiral compounds were determined for all the samples by using gas chromatography and by multidimensional and conventional enantioselective gas chromatography. The composition of the oils was compared with previous studies. The enantiomeric distribution of lemon petitgrain oils is here reported for the first time. On the composition of mandarin petitgrain oil, the information available in literature, to date, is relative only to one sample from Egypt. Carbon isotope ratio of several terpene hydrocarbons and of their oxygenated derivatives contained in petitgrains was compared with the δ ¹³C_VPDB values of the same compounds present in the corresponding genuine Italian Citrus peel oil. The results prove that the isotopic values obtained for lemon and mandarin petitgrain oils are very close to those relative to the corresponding peel oils determined in previous studies.     

Monitoring chlorophenols in industrial effluents by solid-phase microextraction–gas chromatography–mass spectrometry

A method for the determination of 19 chlorophenols in industrial effluents samples using solid-phase microextraction (SPME) coupled to gas chromatography–mass spectrometry has been developed. Four kinds of different SPME fibres have been studied. Among them, the polyacrylate and carbowax®-divinylbenzene fibres were the most adequate. The extraction process was optimized by means of the experimental design, which allows the study of a large number of factors with a reasonable number of experiments. The optimized method allows the determination of the studied chlorophenols in complex matrices with a high organic content with detection limits down to 0.07?ng?mL^?1 and RSD ranging from 4.4% to 13.8%. The recovery studies with spiked real effluent samples at low levels of chlorophenols ranged from 59.8% to 142.1% for the lowest level (0.5?ng?mL^?1) and from 79.6% to 115.8% for the highest spiked level (2?ng?mL^?1). These results show the suitability of the proposed method to monitor chlorophenols in complex samples. 2,4,5-TCP was detected at concentrations close to its limits of detection in effluents coming from an oil refinery.     

Derivatization of pinacolyl alcohol with phenyldimethylchlorosilane for enhanced detection by gas chromatography–mass spectrometry

A derivatization procedure for the qualitative gas chromatography–mass spectrometry (GC-MS) analysis of pinacolyl alcohol (PA) that employs phenyldimethylchlorosilane (PhDMClS) and the promoter N-methylimidazole is described. While PA, underivatized, can be detected using conventional gas chromatographic methods, its polarity and low boiling point make its detection in complex matrices challenging. The silylation procedure described herein generates a PA-derivative exhibiting an increased on-column retention time, thus shifting its GC-MS signal away from commonly encountered, volatile, interfering analytes. Derivatized PA could be distinguished from other PhDMClS-derivatized isomeric alcohols by its unique retention time and mass spectrum. The derivatization was demonstrated to perform well in the GC-MS analysis and identification of PA in samples from Proficiency Tests administered by the Organisation for the Prohibition of Chemical Weapons (OPCW).

Multiresidue analysis of pollutants as their trimethylsilyl derivatives,by gas chromatography–mass spectrometry

This paper reports a multiresidue analysis procedure which permits the identification and quantification of sixty-three water-soluble pollutants. Subsequent to their solid-phase extraction (SPE) enrichment, analyses of species have been carried out from one solution, by a single injection, as their trimethylsilyl-oxime ether/ester derivatives, by gas chromatography–mass spectrometry, within 31 min. Based on our optimized extraction, derivatization and mass fragmentation studies separation have been performed in the total ion current mode, identification and quantification of compounds have been carried out on the basis of their selective fragment ions. Including various pharmaceuticals, benzoic acid, its substituted species, different aromatic carboxylic acids, cholic acids, unsaturated and saturated fatty acids, aliphatic dicarboxylic acids, as well as synthetic pollutants of various origins (2,4-di-tert-butylphenol, different phthalates). Standard compounds were added to 500 mL effluent wastewater samples, at three concentrations (1–5 μg/L, 5–10 μg/L and 10–20 μg/L). Recoveries, using the Waters Oasis cartridges performing extractions at pH 2, pH 4 and pH 7 proved to be the optimum at pH 4 (average recoveries (94.5%), except for cholesterol (10%), paracetamol (18%) and 2,5-dihydroxybenzoic acid (25%). Carbamazepine could be recovered at pH 7, only. Responses, obtained with derivatized standards proved to be linear in the range of 4–80 μg/L levels. Limit of quantitation values varied between 0.92 ng/L (4-hydroxyphenylacetic acid) and 600 ng/L (dehydrocholic acid) concentrations. One of the most important messages of this work is the confirmation of the origin of blank values. It was shown that contaminants, mainly 2,4-di-tert-butylphenol, different phthalates and fatty acids, are sourced both from the reagents and mainly from the SPE procedure, independent on the cartridge applied. Reproducibilities, characterized with the relative standard deviations (RSDs) of measurements, varied between 0.71% and 10%, with an average of 4.38% RSD. The practical utility of the method was shown by the identification and quantification of the pollutant contents of Hungarian influent and effluent wastewaters (for six consecutive months and that of the Danube River for 2 months).     

Analysis of 28 insecticides in curry leaves (Murraya koenigii L.) by gas chromatography and gas chromatography–mass spectrometry

A simple and efficient method was developed for analysis of 28 insecticides (organochlorines, organophosphates and synthetic pyrethroids) in curry leaves (Murraya koenigii L.). The extraction of the analytes was carried out with acidified acetonitrile and purification with magnesium sulphate, primary secondary amine along with graphitised carbon black to remove excess chlorophyll content in curry leaves. Acetonitrile extracts were changed into hexane + acetone (9 + 1) and hexane + toluene (9 + 1) in the final step. In another method ethyl acetate was used for extraction and purification was carried out as above. The analytes in the samples were determined by gas chromatography (GC) and confirmed by gas chromatography–mass spectrometry (GC–MS). Use of ethyl acetate increased the recovery of the analytes, but co-extractive interference led to higher GC maintenance. Acidified acetonitrile was found to be a better extraction solvent compared with ethyl acetate. The use of hexane:toluene (9:1) as exchange solvent increased the recovery of organochlorine insecticides compared with hexane:acetone (9:1). The limit of quantification (LOQ) of the method was 0.01 mg kg^?1 for organochlorine insecticides and 0.05 mg kg^?1 for organophosphates and synthetic pyrethroids. The recoveries of organochlorines were within 70.36–82.45%; organophosphates, 82.54–90.93% and synthetic pyrethroids, 88.45–90.71% at the LOQ level. The method developed was found suitable for analysis of real samples of curry leaves. The pesticides detected in curry leaves collected from the retail market were mainly organophosphates and synthetic pyrethroids.