Headspace GC-MS Research Articles

Automated headspace solid-phase microextraction versus headspace for the analysis of furan in foods by gas chromatography–mass spectrometry

A simple, fast and fully automated method based on headspace solid-phase microextraction coupled on-line with gas chromatography–ion trap mass spectrometry (HS-SPME–GC–ITMS) is proposed for furan determination in foods. The performance of the proposed method was compared to the automated headspace-GC–MS method, proposed by the US Food and Drugs Administration (US FDA), in terms of repeatability, limits of the detection and quantification. Both methods gave similar results for furan determination in selected food samples, although slightly worse precision (RSD%, 9–12%) and higher limits of detection (from 5 to 20 times higher) were obtained by the headspace method. In addition, higher sample throughput in routine furan analysis was obtained using the proposed HS-SPME–GC–ITMS method with isotope dilution than using the US FDA method, which recommends standard addition for quantification. The proposed method provides good precision (RSD% <10%) and low limits of detection, ranging from 0.02 to 0.12 ng g −1 depending on the sample. The developed HS-SPME–GC–MS method was used to analyse furan in several Spanish food commodities and concentrations ranging from 0.1 ng g −1 to 1.1 μg g −1 were found.

Top note compounds of Chinese traditional bacteria-fermented soybean

Top note compounds of Chinese traditional bacteria-fermented soybean were analysed by using headspace sampler, GC and GC-MS. Thirty-three note compounds were identified in Chinese traditional bacteria-fermented soybean. Among them, 28 compounds are responsible for the Chinese traditional bacteria-fermented soybean top note. 3-Methylbutanal (6.690%), amyl nitrite (12.976%), 2-methylpropanoic acid (4.014%), 2,3-butanediol (2.171%), 3-methylbutanoic acid (14.273%), 2-methylbutanoic acid (11.866%), benzeneacetaldehyde (1.422%), nonadecane (3.195%), eicosane (5.331%), heneicosane (23.418%) and docosane (5.011%) were all found in concentrations higher than 1.0% (calculated as % peak area of GC analysis using a DB-5 column).

Development and validation of an automated static headspace gas chromatography–mass spectrometry (SHS-GC–MS) method for monitoring the formation of ethyl methane sulfonate from ethanol and methane sulfonic acid

An automated sample preparation and analysis procedure was developed to monitor the formation of ethyl methane sulfonate from reaction mixtures containing ethanol and methane sulfonic acid. The system is based on a liquid handling robot combined with a static headspace module. The formed ethyl methane sulfonate is analysed after derivatisation with pentafluorothiophenol using static headspace-gas chromatography–mass spectrometry (SHS-GC–MS). Using the automated reaction–derivatisation–headspace GC–MS system, the formation of ethyl methane sulfonate can be monitored in different reaction mixtures under different reaction conditions, including temperature, water content and pH. Excellent linearity, repeatability and robustness were obtained, allowing the system to be used in kinetic studies.

Antagonistic Activities of Volatiles from Four Strains of Bacillus spp. and Paenibacillus spp. Against Soil-Borne Plant Pathogens

The four effective antagonistic Bacillus strains, isolated from the rhizosphere soil of cucumber in a greenhouse, produced antifungal volatiles. These volatiles strongly inhibited the growth of the most tested pathogenic fungi with wide host plants, induced the mycelial morphological abnormalities, and decreased the sclerotoid production of Sclerotinia sclerotiorum in sealed plates. Spores of Botrytis cinerea exposed to these volatiles for 24-48 h in cavity slides cracked and the sporaceous inclusion became brown and effused to the suspension. An interesting phenomenon observed was that all the bacterial volatiles exhibited intense inhibitory activities against the pigment formation of tested pathogenic fungi, including Ascochyta citrullina, Alternaria solani, Alternaria brassicae, and so on. Interactions mediated by microbial volatiles could be widespread in soils, and volatiles may play an important role in reducing disease levels. A phylogenetic analysis based on 16S rDNA sequence placed the four bacteria in three species Paenibacillus polymyxa (BMP-11), Bacillus subtilis (BL02), and Bacillus pumilus (BSH-4 and ZB13). Through headspace sampling and GC-MS analysis, a rich profile was found from B. subtilis and overlapping volatile patterns could be found among the different species. Studies are under the way to find the possible action mechanisms and to seek the effective application of bacterial volatiles in greenhouse.

Volatile profile of Stilton cheeses: Differences between zones within a cheese and dairies

Penicillium roqueforti grows and sporulates during the ripening period of blue cheeses and it is responsible for the typical blue cheese flavour formation. However, the sporulation (blue veins) is taking place in a fraction of the total mass and the cheese matrix is highly heterogeneous. The aroma profiles regarding the three different sections of Stilton cheese, blue veins outer crust and white core, were studied using solvent extraction GC–MS, a headspace GC–MS technique (SPME GC–MS) and direct headspace analysis (APCI–MS). Cheeses from different dairies were analysed, allowing the question of how similar are different batches of cheese from different dairies. APCI–MS was good for rapid discrimination of the different cheese profiles. However, the analysis was affected by the presence of ammonia in the headspace. SPME GC–MS produced a large amount of information for screening differences between the sections of the cheese and dairies. Overall, the blue and the outer crust had similar profiles. These two sections contained the higher amount of ketones, while the white contained higher amounts of alcohols and aldehydes.

Headspace gas chromatography–mass spectrometry determination of alkylpyrazines in cocoa liquor samples

This paper proposes a fast, accurate, and quantitative method for alkylpyrazines determination in cocoa liquors samples using gas chromatography with ion trap mass spectrometry detection (GC/IT-MS) and on-line headspace (HS) sample introduction. The optimization of the experimental conditions of the headspace gas chromatography–mass spectrometry (HS–GC–MS) system was carried out using the univariate method, aiming to find a compromise between time of the analysis, sensitivity and pyrazine resolution in a Carbowax (AV-WAX) fused silica capillary column. The procedure was validated through accuracy and precision studies. The results showed a highly satisfactory accuracy rate for the method with a relative standard deviation (RSD) during 1 day and between days of <5.0% ( n = 5). On the other hand, the recovery percentages (94–99%) were quantitative in all cases, with a RSD of <4.0% ( n = 5). Finally, the use the on-line headspace extraction step simultaneously with the analytes separation and detection of the previous sample injection increased the analysis frequency to 3 samples/h. A total of 120 cocoa liquor samples were analyzed.

Identification of Potential Migrants in Epoxy Phenolic Can Coatings

A test protocol has been developed that contains a suite of complementary analytical methods to identify and estimate the concentrations of potential chemical migrants in polymeric coatings applied to metal substrates. The capabilities of these techniques (FT-IR, overall migration, headspace GC-MS, GC-MS, and LC-TOF-MS) have been tested for a variety of polymeric coatings, and the results for one particular coating, an epoxy phenolic, are described as an example. The example provided shows both the power and the limitations of current analytical techniques in the evaluation of the total migrate from food contact materials.

Characterization of Fennel Flavors by Solid Phase Trapping-Solvent Extraction and Gas Chromatography-Mass Spectrometry

Headspace solid phase trapping solvent extraction (HS-SPTE) and GC-MS was applied for the characterization of volatile flavors from fennel, anise seed, star-anise, dill seed, fennel bean, and Ricard aperitif liquor. Tenax was used for HS-SPTE adsorption material. Recoveries, precision, linear dynamic ranges, and the limit of detection in the analytical method were validated. There were some similarities and distinct differences between fennel-like samples. The Korean and the Chinese fennels contained trans-anethole, (+)-limonene, anisealdehyde, methyl chavicol as major components. The volatile aroma components from star anise were characterised by rich trans-anethole, (+)-limonene, methyl chavicol, and anisaldehyde. Additionally, principal component analysis (PCA) has been used for characterizing or classifying eight different fennel-like samples according to origin or other features. A quite different pattern of dill seed was found due to the presence of apiol (dill).

Analysis of volatile constituents isolated by hydrodistillation and headspace solid‐phase microextraction from Adenostyles briquetii Gamisans

The volatile fraction of the whole plant and separated organs of Adenostyles briquetii Gamisans (syn. Cacalia briquetii; family Asteraceae), an endemic species from Corsica, has been studied by headspace solid-phase microextraction (HS-SPME), GC and GC-MS(EI and CI). A total of 141 components were identified, representing 93% of the entire amount. The volatile fraction was characterised by sesquiterpene hydrocarbons (52.8%) and oxygenated sesquiterpenes (25.9%). The major components were germacrene D (18.5%), zingiberene (12.9%) and beta-oplopenone (10.8%). The influence of HS-SPME parameters on the extraction of family components is reported for the first time.

Determination of Aroma Compounds from Alcoholic Beverages in Spiked Blood Samples by Means of Dynamic Headspace GC–MS

Some aroma compounds found in alcoholic beverages are characteristic of a certain beverage (i.e. 2,4-decadienoic acid ethyl ester is characteristic of pear spirit and 5-butyltetrahydro-4-methylfuran-2-on “whiskey lactone” is characteristic of aged spirits like whiskey). These substances were detectable in beverages but not in blood samples. The aim of this investigation was to find a sensitive sampling technique for aroma compounds in whole blood samples. This technique may be used in forensic toxicology for examination of drinking claims. The method comprises dynamic headspace sampling using a purge and trap concentrator, followed by quantitative gas chromatography–mass spectrometry (dynamic HS–GC–MS). The influence of sample preparation, trap adsorbents and sample temperature as well as desorption time and purge time on the quality of the analytical results were investigated. The following optimal parameters were determined: stirred and diluted whole blood sample without salt addition, use of Carbotrap C as trap material, sample temperature at 80 °C, desorption time 20 min and purge time 30 min. These optimal parameters were used for the determination of detection limits (LOD). The LOD of aroma compounds by means of dynamic headspace sampling were compared with the results of conventional sampling: the static headspace technique. Limits of detection for the aroma compounds with conventional static headspace GC are in the range 400–10,000 μg L−1. Dynamic headspace–GC was found to be a more sensitive sampling technique for most of the aroma compounds investigated (e.g. C4–C8 ethyl esters, benzoic acid ethyl ester, linalool oxide and 4-ethylguaiacol) with detection limits between 1 and 50 μg L−1, but there were also limits to the sampling of substances with lower volatility like decanoic acid ethyl ester, 2,4-decadienoic acid ethyl ester, eugenol and whiskey lactone with detection limits of about 1,000 μg L−1.

Electrochemical stability of organic electrolytes in supercapacitors: Spectroscopy and gas analysis of decomposition products

The fundamental aging mechanisms in double-layer capacitors based on alkylammonium electrolytes in acetonitrile were clarified for the first time. After abusive testing at cell voltages above 4 V, ultracapacitors cast out a crystalline mass of residual electrolyte, organic acids, acetamide, aromatics, and polymer compounds. The mixture could be reproduced by electrolysis. The decomposition products of active carbon electrodes and electrolyte solution after a heat treatment at 70 °C were identified by infrared and ultraviolet spectroscopy, liquid and headspace GC–MS, thermogravimetric analysis, and X-ray diffraction. The alkylammonium cation is destroyed by the elimination of ethene. The fluoroborate anion works as source of fluoride and hydrogenfluoride, and boric acid derivates. Acetonitrile forms acetamide, acetic and fluoroacetic acid, and derivates thereof. Due to the catalytic activity of the electrode, heterocyclic compounds are generated in the liquid phase. The etched aluminium support under the active carbon layer is locally destroyed by fluorination. Exploring novel electrolytes, ionic liquids were characterized by impedance spectroscopy.

Protein and Lipid Oxidation during Frozen Storage of Rainbow Trout (Oncorhynchus mykiss)

This study aimed at investigating protein and lipid oxidation during frozen storage of rainbow trout. Rainbow trout fillets were stored for 13 months at -20, -30, or -80 degrees C, and samples were analyzed at regular intervals for lipid and protein oxidation markers. Lipid oxidation was followed by measuring lipid hydroperoxides (PV), as well as secondary oxidation products (volatiles) using dynamic headspace GC-MS. Free fatty acids (FFA) were measured as an estimation of lipolysis. Protein oxidation was followed using the spectrophotometric determination of protein carbonyls and immunoblotting. Significant oxidation was observed in samples stored at -20 degrees C, and at this temperature lipid and protein oxidation seemed to develop simultaneously. FFA, PV, and carbonyls increased significantly for the fish stored at -20 degrees C, whereas the fish stored at -30 and -80 degrees C did not show any increase in oxidation during the entire storage period when these methods were used. In contrast, the more sensitive GC-MS method used for measurement of the volatiles showed that the fish stored at -30 degrees C oxidized more quickly than those stored at -80 degrees C. Detection of protein oxidation using immunoblotting revealed that high molecular weight proteins were oxidized already at t = 0 and that no new protein oxidized during storage irrespective of the storage time and temperature. The results emphasize the need for the development of more sensitive and reliable methods to study protein oxidation in order to gain more explicit knowledge about the significance of protein oxidation for food quality and, especially, to correlate protein oxidation with physical and functional properties of foods.

Identification and Quantification of a Marker Compound for ‘Pepper' Aroma and Flavor in Shiraz Grape Berries by Combination of Chemometrics and Gas Chromatography−Mass Spectrometry

'Black pepper' aroma and flavor is important to some Australian Shiraz red wine styles but the aroma compounds involved have yet to be identified, and no objective analytical method to assess 'pepper' grape aromas is available to date. Samples of potentially 'spicy'/'peppery' grapes were obtained from vineyards in South Australia and Victoria over two vintages. The important sensory attributes of the grapes, including the aroma descriptor 'pepper', were rated by a sensory panel. The sensory study revealed a strong correlation between the intensity of 'pepper' aroma and the intensity of 'pepper' flavor perceived on the palate. The grape homogenates were analyzed by static headspace GC-MS using a cool inlet system. Vectors obtained by analysis of over 13 000 individual mass spectra per grape sample were then subjected to multivariate analyses. Both principal component analysis and partial least-squares regression were used to develop multivariate models based on mass spectra and aroma descriptors to explain the intensity of the rating of the 'pepper' character. Corresponding differences in mass spectra and aroma were observed among vineyards and from the same vineyards in different years. Additional optimization of the methodology enabled selection of a single region of the GC-MS chromatogram that allowed prediction of 'pepper' aroma intensity with a correlation coefficient >0.98 and led to the identification of alpha-ylangene, a tricyclic sesquiterpene. To assess the potential of alpha-ylangene as a marker for this sensory characteristic, a method for alpha-ylangene analysis of grapes and wine using HS-SPME-GC-MS was developed. Although not a significant aroma compound by itself, alpha-ylangene was a satisfactory marker for the 'pepper' aroma in grapes and wine, and its concentration showed similar discrimination between 'peppery' vineyards and vintages as that obtained using the multivariate models. Despite its presence in grapes, we could not detect alpha-ylangene in wine.

NATURAL COMPOUNDS OF PALESTINE FLORA. COMPARISON ANALYSIS BY STATIC HEADSPACE AND STEAM DISTILLATION GC-MS OF SEMIVOLATILE SECONDARY METABOLITES FROM LEAVES OF CULTIVATED PALESTINIAN MAJORANA SYRIACA

A comparative analysis by using static headspace (HS) and steam distillation (SD) GC-MS of the volatile and the semi-volatile secondary metabolites from leaves of cultivated Majorana syriaca. The essential oils endogenous to cultivated thyme were isolated and identified by HS-GC-MS technology and compared to those from SD-GC-MS. The HS-GC-MS results showed that the Palestinian cultivated thyme is rich in monoterpene hydrocarbons and phenolic monoterpenes such as alpha-phellandrene, alpha-pinene, beta-myrcene, m-cymene, p-cymene, gamma-terpinene, thymol and carvacrol. In all the samples gamma-terpinene, p-cymene, thymol and carvacrol were the most abundant compounds. HS and SD-GC-MS have proved that most of the cultivated thyme samples examined has thymol isomer as the major phenolic constituent.

Headspace–mass spectrometry determination of benzene, toluene and the mixture of ethylbenzene and xylene isomers in soil samples using chemometrics

A simple and fast method has been developed for the determination of benzene, toluene and the mixture of ethylbenzene and xylene isomers (BTEX) in soils. Samples were introduced in 10 mL standard glass vials of a headspace (HS) autosampler together with 150 μL of 2,6,10,14-tetramethylpentadecane, heated at 90 °C for 10 min and introduced in the mass spectrometer by using a transfer line heated at 250 °C as interface. The volatile fraction of samples was directly introduced into the source of the mass spectrometer which was scanned from m/ z 75 to 110. A partial least squares (PLS) multivariate calibration approach based on a classical 3 3 calibration model was build with mixtures of benzene, toluene and o-xylene in 2,6,10,14-tetramethylpentadecane for BTEX determination. Results obtained for BTEX analysis by HS–MS in different types of soil samples were comparables to those obtained by the reference HS–GC–MS procedure. So, the developed procedure allowed a fast identification and prediction of BTEX present in the samples without a prior chromatographic separation.

Gas chromatography‐mass spectrometry following pressurized hot water extraction and solid‐phase microextraction for quantification of eucalyptol, camphor, and borneol in Chrysanthemum flowers

Chrysanthemum flower is a common traditional Chinese medicine (TCM). In this work, pressurized hot water extraction (PHWE) followed by headspace solid-phase microextraction (HS-SPME) and GC-MS was developed for the determination of three main active volatile compounds of eucalyptol, camphor, and borneol in Chrysanthemum flowers from four different growing areas in China by internal standard method. The parameters of PHWE and HS-SPME were optimized. The method was also validated. The results showed that PHWE-SPME-GC-MS is a simple, rapid, efficient, and solvent-free technique for the quantitative determination of eucalyptol, camphor, and borneol in TCMs and is potentially useful for the TCM quality assessment.

Analysis of furan in foods. Is headspace sampling a fit-for-purpose technique?

Headspace GC-MS has been opitimized for the determination of furan in foods. The conditions of sample preparation, headspace sampling and GC separation were optimized to enhance sensitivity during GC-MS analysis. Green coffee was used to prepare a matrix matched calibration curve for furan. However, it was unexpectedly found that a green coffee sample was not blank. GC-MS analysis performed after equilibration for 30 min at 40°C showed the presence of 4.2 ng/g furan in green coffee. In order to understand whether furan was naturally present or formed during headspace sampling, green coffee was investigated in time-dependent manner at headspace equilibration temperatures of 40 and 70°C. It was observed that furan response continued to increase in a way similar to first order formation kinetics. The same behavior was found for freshly squeezed tomato and orange juices leading to the suspicion of furan formation during headspace equilibration. It is concluded that a matrix matched calibration for each particular food matrix is necessary to compensate for furan formation during headspace sampling, and thus, to quantify furan more accurately.

Bread making using kefir grains as baker’s yeast

The leavening activity of kefir grains in lean dough and their efficiency in producing bread of good quality, in terms of loaf volume, flavour, texture and shelf life, were evaluated. Although the leavening rate of commercial baker’s yeast was higher (30 ml/h), kefir performed well (24 ml/h), and produced bread of good quality, resembling traditional sourdough bread. Rising was satisfactory (specific loaf volume 3.0–3.3 ml/g) and breads produced with kefir retained more moisture, had a firmer texture, lower acidity (pH 4.9–5.5) and retained their freshness for longer compared to baker’s yeast bread. Consumers showed a preference for kefir-leavened bread, although a preliminary headspace GC–MS analysis of volatiles did not reveal significant differences between the two types of bread.

Effect of [Mn(acac) 3] and its combination with 2,2′-bipyridine on the autoxidation and oligomerisation of ethyl linoleate

In this study we investigated the autoxidation and oligomerisation of ethyl linoleate (EL) catalysed by [Mn(III)(acac) 3] (acac=2,4-pentanedionate) and its combination with 2,2-bipyridine (bpy), in comparison with the EL catalysed by Co(II) 2-ethylhexanoate (Co-EH). EL is a model compound for the alkyd resin in alkyd paints, Co-EH is a common drying catalyst for alkyd paints, and [Mn(acac) 3] and the [Mn(acac) 3]/bpy combination are potential new drying catalysts. The autoxidation of EL was studied through time-resolved Raman spectroscopy, oxygen uptake measurements, and peroxide amount determination. To follow the oligomerisation of EL in time, size exclusion chromatography was used. Head-space GC-MS measurements were performed to determine the amounts of hexanal and pentanal that were formed as volatile byproducts during the autoxidation of EL. The autoxidation rates of EL in the presence of Co-EH and [Mn(acac) 3]/bpy were found to be similar, while the rate in the presence of [Mn(acac) 3] was slower. The extent of EL oligomerisation was much higher for [Mn(acac) 3] compared to the other catalysts. Different mechanisms are proposed for the mode of action for each of the catalysts: Co-EH is primarily a hydroperoxide decomposition catalyst, as is [Mn(acac) 3], only less active. The [Mn(acac) 3]/bpy combination probably forms the very reactive complexes [Mn(III)(acac) 2(bpy)] + and [Mn(II)(acac) 2(bpy)], which are responsible for a very high autoxidation rate, but also for significant degradation of the formed EL oligomers via β-scission reactions due to the promotion of alkoxy radical formation.

Determination of alpha-bisabolol in human blood by micro-HPLC–ion trap MS and head space-GC–MS methods

Alpha-bisabolol is a compound present in some essential oils, widely distributed in several plants, including camomile. Two different methods for analysing an essential oil, such as alpha-bisabolol in human blood are reported: the first uses micro-liquid chromatography–electrospray ionisation-mass spectrometry (μHPLC–ESI-MS), whereas the second is based on “head space” injection coupled to gas chromatography–mass spectrometry (HS-GC–MS). For LC–ESI-MS, human blood samples, spiked with alpha-bisabolol, were extracted with hexane and evaporated to dryness under air stream. The residue was then reconstituted with methanol and injected into a C18 column, connected to an ion trap mass spectrometer equipped with an ESI source. Spectra were recorded in the positive ion, selected ion monitoring mode. The detection limit of alpha-bisabolol in blood was 0.125 μmol/l. The preparation of samples for the analysis in HS-GC–MS was limited to blood dilution with water (0.5 ml blood + 1 ml water). Head space vials were heated at 125 °C for 1 h before automatic injection. The HS-GC–MS detection limit (0.13 μmol/l) was similar to that achieved with the μHPLC–ESI-MS method. Successful tests were performed to verify if alpha-bisabolol could be directly measured by the HS-GC–MS method in different biological samples (blood, urine, faeces, homogenate tissues) from rats treated with the camomile essential oil.