Comparison of comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry and gas chromatography-mass spectrometry for the qualitative characterisation of roasted barley by solid-phase microextraction

Volatile compounds of roasted barley used in the production of barley coffee, the most common coffee substitute, were analysed by using solid-phase microextraction (SPME) followed by GC-MS and comprehensive GC x GC-TOF-MS, respectively. The optimised SPME extraction conditions in terms of selection of the fibre coating, extraction time and extraction temperature allowed to obtain the highest GC response, thus enhancing the identification capabilities of the developed method. As for the SPME-GC x GC-TOF-MS analysis, 64 compounds with similarity, reverse and probability values above 800, 900 and 6000, respectively, were identified, by using a polar x apolar column set combination; in contrast, GC-MS was able to identify a lower number of compounds, i.e. 40 volatiles.     

Application of solid-phase micro-extraction and comprehensive two-dimensional gas chromatography (GC×GC) for flavour analysis

Summary Headspace solid-phase micro-extraction (HS SPME), comprehensive two-dimensional GC (GC×GC), and flame ionization detection (FID) have been examined for their suitability and compatibility for rapid sampling, separation, and detection of garlic flavour volatiles. This approach (HS-SPME-GC×GC-FID) is distinctly superior to use of one-dimensional GC, i. e., HS-SPME-GC-FID. Direct comparison of the experimental results showed that a 10–50-fold increase in sensitivity is obtained, separating power is substantially enhanced, and the peak capacity is up to ten times higher. As a consequence, much more detailed flavour analysis can be performed; this results in better information about the aroma-active compounds.     

Headspace solid-phase microextraction combined with comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry for the determination of volatile compounds from marine salt

In this work, a methodology to characterise the volatile and semi-volatile compounds from marine salt by headspace solid-phase microextraction (HS-SPME) and comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC × GC/TOFMS) was developed. Samples from two saltpans of Aveiro, in Portugal, with diverse locations, obtained over three years (2004, 2005, and 2007) were analysed. A 50/30 μm divinylbenzene/carboxen/polydimethylsiloxane SPME fibre was used. The volatiles present in the headspace of the solid salt samples (crystals) were equilibrated overnight at 60 °C and extracted for 60 min prior to injection in the GC × GC/TOFMS. 157 compounds, distributed over the chemical groups of hydrocarbons, aldehydes, esters, furans, haloalkanes, ketones, ethers, alcohols, terpenoids, C₁₃ norisoprenoids, and lactones were detected across the samples. Furans, haloalkanes and ethers were identified for the first time in marine salt. The large number of co-elutions on the first column that were resolved by the GC × GC system revealed the complexity of marine salt volatile composition. The existence of a structured 2D chromatographic behaviour according to volatility, in the first dimension (¹D), and primarily polarity, in the second dimension (²D), was demonstrated, allowing more reliable identifications. The resolution and sensitivity of GC × GC/TOFMS enabled the separation and identification of a higher number of volatile compounds compared to GC–qMS, allowing a deeper characterisation of this natural product.     

Comprehensive multidimensional GC for the characterization of roasted coffee beans

The present investigation is based on the separation of one of the most complex food matrices: the roasted coffee bean volatile fraction. Analysis of the two main species of coffee (Arabica/Robusta) was achieved through an effective and simple sampling procedure, headspace solid-phase microextraction (SPME), and the unprecedented resolving power of comprehensive gas chromatography (GC x GC). The combination of these two techniques proved to be a powerful tool for the extraction and separation of coffee volatiles. In fact, thousands of compounds that play various roles in the constitution of coffee aroma profile were resolved in the 2-D contour plot, each occupying a specific position pinpointed by two retention time coordinates. The potential use of this method for the assessment of coffee quality and the detection of commercial fraud is discussed. The potential of GC x GC for identification and classification of unknowns was also demonstrated, as the formation of characteristic patterns for structurally related compounds was observed in the bidimensional chromatogram. Moreover, reproducibility results were supported by the use of an autosampler for SPME applications that allowed any inaccuracy arising from manual handling to be avoided.     

Enantiomeric monoterpene emissions from natural and damaged Scots pine in a boreal coniferous forest measured using solid-phase microextraction and gas chromatography/mass spectrometry

In order to develop a valuable method for accurate screening of biogenic emissions from undisturbed living plants or for plant-insect interactions, solid-phase microextraction (SPME) has been combined with dynamic branch enclosure cuvettes and enantioselective GC/MS. The study was conducted at Hyyti?l? forest station, Finland within a boreal coniferous forest dominated by Scots pine (Pinus sylvestris). The SPME method was optimized for monoterpenes by testing three fibre coatings: polydimethylsiloxane (PDMS), polydimethylsiloxane/divinylbenzene (PDMS/DVB) and carbowax/divinylbenzene (CW/DVB) and determining the optimum exposure time. The PDMS/DVB fibre was found to be most suitable and was used to characterize emissions of P. sylvestris enclosed in dynamic branch enclosure cuvettes by exposure for 1 min followed by desorption and separation on a beta-cyclodextrin column installed in the GC/MS oven. Dynamic cuvette measurements have been compared to static headspace SPME samples of the emission of detached needles from the same tree species and a portable dynamic air sampler (PDAS)-SPME for sampling the ambient air around the same trees. The method developed has allowed an accurate characterization of the gaseous emission of P. sylvestris and the identification of 17 isoprenoids comprising chiral and achiral monoterpenes. Two chemotypes of Scots pine can be differentiated through their emission of (+)-delta-3-carene. While SPME-dynamic cuvette, portable dynamic sampler and absorbent results agreed well, significant differences in enantiomeric ratios were observed in natural emissions and those of damaged leaves. Therefore, in enantioselective studies of plant-insect and/or plant-plant interactions, the two enantiomers of a given monoterpene should be treated as two separate substances.     

固相微萃取-气相色谱/质谱分析栀子花的头香成分

 分别用固相微萃取和动态顶空法分离栀子鲜花的头香成分,用GC/MS技术分析鉴定,并用GC/MS总离子流色谱峰的峰面积进行归一化定量。在固相微萃取方法中,共鉴定了54种化学成分,占总峰面积的99.98%。主要成分(质量分数)依次为金合欢烯（64.86%）、罗勒烯（29.33%）、芳樟醇（2.74%）、惕各酸顺式叶醇酯（1.34%）和苯甲酸甲酯（0.25%）等。经与动态顶空法的分析结果比较发现,固相微萃取法不仅操作简便,而且具有较高的采样灵敏度,获得的化学成分的信息量多于动态顶空法。     

Possible interest of various sample transfer techniques for fast gas chromatography-mass spectrometric analysis of true onion volatiles

We improved GC-MS analysis of onion volatiles by comparing organic solvent partition with solid-phase microextraction (SPME) following cryo-trapping isolation and by comparing the same extraction methods on direct onion juice. Cryotrapping produces very small quantities of volatiles and therefore is not a suitable extraction method for GC-MS analysis. We confirm that SPME accelerates the degradation of labile thiosulfinates but the lacrymatory factor remains intact. The identification of Allium thiosulfinates is only obtained on juice extracted by diethyl ether using a fast GC-MS analysis on a 10 m X 0.3 mm column of 4 microm coating, with routine splitless injection. The lacrymatory factor is best analysed directly on fresh onion juice by SPME with the same chromatographic conditions. To characterise and to quantify all the true onion volatiles, we propose to analyse the same sample by successive SPME-GC-MS and solvent extraction-GC-MS.     

Chemical causes of the typical burnt smell after accidental fires

The components responsible for the typical burnt smell that occurs after accidental fires (e.g. in buildings) were identified. For this purpose, samples of odorous materials were taken from different real fire sites. Their volatile fractions were analysed by means of thermal desorption, headspace analysis and solid-phase microextraction (SPME) combined with gas chromatography–mass spectrometry (GC/MS). Measurements performed with SPME gave the highest number of analytes as well as the highest signal intensities. A divinylbenzene/carboxen/polydimethylsiloxane SPME fibre was found to be the most suitable for this task. To distinguish the odour-active compounds from the ca. 1,400 identified volatiles concentrated by SPME, an olfactory detection port was attached to the GC/MS and the column effluent was assessed by panellists. The results revealed that eleven odorous compounds were present in most of the investigated samples: acetophenone, benzyl alcohol, 4-ethyl-2-methoxyphenol, 2-hydroxybenzaldehyde, 2-hydroxy-5-methylbenzldehyde, 2-methoxyphenol, 2-methoxy-4-methylphenol, 2-methylphenol, 3-methylphenol, 4-methylphenol and naphthalene. Their odour activities were confirmed in additional olfactory experiments, and the relative ratios of these eleven compounds were determined. Based on these ratios, standard solutions that presented an intense odour with typical characteristics of the burnt smell were produced.     

High-throughput analysis of bergamot essential oil by fast solid-phase microextraction-capillary gas chromatography-flame ionization detection

The advantages of using a narrow-bore column in headspace solid-phase microextraction-gas chromatographic (HS-SPME-GC) analysis are investigated. An automated rapid HS-SPME-GC method for the determination of volatile compounds in a complex sample (bergamot essential oil) was developed. A low-capacity (7 microm) SPME fibre was employed, enabling a short equilibration time (15 min). The absorbed volatile compounds were then separated in 12.5 min on a 10 m x 0.1 mm I.D. capillary. The fast GC method was characterized by relatively moderate GC parameters (head pressure: 173 kPa; temperature program rate: 12 degrees C/min). The employment of the low-capacity fibre also suited the reduced sample capacity of the capillary employed, hence column overloading was avoided. Analytical repeatibility was determined in terms of retention times (maximum RSD: 0.32%) and peak areas (maximum RSD: 9.80%). The results obtained were compared to those derived from a conventional HS-SPME-GC (a 30 microm SPME fibre and 0.25 mm I.D. capillary were used) application on the same sample. In this respect, a great reduction of analytical time was obtained both with regard to the conventional SPME equilibration and GC run times, which both required 50 min. Peak resolution was altogether comparable in both applications. Although a slight loss in terms of sensitivity was observed in the rapid approach (generally within the 25-50% range), this did not impair the detection of all peaks of interest. Finally, the selectivities of the 30 and 7 microm fibres were evaluated and, as expected, these were in good agreement.     

Formation of artefacts during air analysis of volatile amines by solid-phase micro extraction.

Solid-phase micro extraction (SPME) is a promising technique for fast and low cost trace analysis. However, some limitations of the technique were encountered when using a PDMS (polydimethylsiloxane)/Carboxen fibre for sampling a mixture of volatile aliphatic amines in air. On the GC chromatogram, two supplementary peaks were noticed in addition to the analyte peaks, thus limiting qualitative and quantitative analysis in this particular case. This paper presents the investigations to identify the artefacts and determine the origin of their formation. First, GC-MS identification, by both electron impact and chemical ionisation modes, demonstrated that the two artefacts were unsaturated amines assumed to be formed by a dehydrogenation reaction of the target amines. This reaction was found to occur during thermal desorption of analytes in the GC injection port and to be catalysed by temperature and by metals consisting of the inox (stainless-steel) needle of the SPME device. It was also demonstrated that artefact formation was not significant when using PDMS or PDMS/divinylbenzene fibres. This difference with PDMS/Carboxen fibre can be explained by the high desorption temperature required for this fibre. Moreover, the microporosity of Carboxen induces a longer desorption time which increases the contact between analytes and inox and thereby enhances artefact formation.     

Comparison of Different Analytical Methods for Volatile and Odour-Active Substances in Polyolefins

Emissions of volatiles of polymeric materials are an important parameter for materials characterisation, and gain more and more importance either by their odour activity or by other undesired behaviour. Currently, numerous methods are applied for the determination of volatiles, but all of them use gas chromatography (GC) with different detectors. The information gained by flame ionisation detection (FID) is the total emitted volatiles expressed as a sum value, but no further deeper information is provided. Additionally, due to different sample amounts, preparation, way of sampling and GC parameters, results cannot be compared to each other. Also, determination of single sum values by integrating the total area of volatiles is of little help for material development due to the lack of detailed information about chemical composition, and other methods have to be applied. Other compounds of interest such as odour-active ones turn up in only very small amounts and cannot be detected by these methods as an extensive analytical sample preparation is necessary. We compare results obtained by different sample preparation techniques used in industrial standards (VDA 277 and VDA278) to scientific alternatives such as Solid Phase Microextraction (SPME) coupled to GC with mass spectrometry (MS) and Simultaneous Distillation/Extraction SDE coupled to GC-MS to demonstrate capabilities and applicability of each method.     

Analysis of virgin olive oil volatile compounds by headspace solid-phase microextraction coupled to gas chromatography with mass spectrometric and flame ionization detection

The efficiency of headspace solid-phase microextraction (SPME) was evaluated for the qualitative and semi-quantitative analysis of virgin olive oil volatile compounds. The behaviour of four fibre coatings was compared for sensitivity, repeatability and linearity of response. A divinylbenzene-Carboxen-polydimethylsiloxane fibre coating was found to be the most suitable for the analysis of virgin olive oil volatiles. Sampling and chromatographic conditions were examined and the SPME method, coupled to GC with MS and flame ionization detection, was applied to virgin olive oil samples. More than 100 compounds were isolated and characterised. The presence of some of these compounds in virgin olive oil has not previously been reported. The main volatile compounds present in the oil samples were determined quantitatively.     

Volatile Profile of Portuguese Monofloral Honeys: Significance in Botanical Origin Determination

The volatile profiles of 51 samples from 12 monofloral-labelled Portuguese honey types were assessed. Honeys of bell heather, carob tree, chestnut, eucalyptus, incense, lavender, orange, rape, raspberry, rosemary, sunflower and strawberry tree were collected from several regions from mainland Portugal and from the Azores Islands. When available, the corresponding flower volatiles were comparatively evaluated. Honey volatiles were isolated using two different extraction methods, solid-phase microextraction (SPME) and hydrodistillation (HD), with HD proving to be more effective in the number of volatiles extracted. Agglomerative cluster analysis of honey HD volatiles evidenced two main clusters, one of which had nine sub-clusters. Components grouped by biosynthetic pathway defined alkanes and fatty acids as dominant, namely n-nonadecane, n-heneicosane, n-tricosane and n-pentacosane and palmitic, linoleic and oleic acids. Oxygen-containing monoterpenes, such as cis- and trans-linalool oxide (furanoid), hotrienol and the apocarotenoid α-isophorone, were also present in lower amounts. Aromatic amino acid derivatives were also identified, namely benzene acetaldehyde and 3,4,5-trimethylphenol. Fully grown classification tree analysis allowed the identification of the most relevant volatiles for discriminating the different honey types. Twelve volatile compounds were enough to fully discriminate eleven honey types (92%) according to the botanical origin.     

Improved determination of flavour compounds in butter by solid-phase (micro)extraction and comprehensive two-dimensional gas chromatography

The practicability and potential of comprehensive two-dimensional gas chromatography (GC x GC) coupled to both conventional flame ionisation (FID) and time-of-flight mass spectrometric (TOF-MS) detection, were compared with those of conventional one-dimensional (1D) GC, with the determination of flavour compounds in butter as an application. For polar flavour compounds, which were collected from the aqueous fraction of butter by means of solid-phase extraction (SPE), it was found that GC x GC dramatically improves the overall separation. Consequently, quantification and preliminary identification based on the use of ordered structures, can be performed more reliably. The improvement effected by replacing 1D-GC by GC x GC is considerable also in the case of TOF-MS detection, as illustrated by the high match factors generally obtained during identification. GC x GC was also used successfully for the characterisation of volatile flavour compounds in the headspace of butter collected by solid-phase microextraction (SPME) and to study the effect of heat treatment on the composition of butter samples in more detail.     

Laboratory and field experiments used to identify<Emphasis Type="Italic"> Canis lupus</Emphasis> var. <Emphasis Type="Italic">familiaris</Emphasis> active odor signature chemicals from drugs,explosives, and humans

This paper describes the use of headspace solid-phase microextraction (SPME) combined with gas chromatography to identify the signature odors that law enforcement-certified detector dogs alert to when searching for drugs, explosives, and humans. Background information is provided on the many types of detector dog available and specific samples highlighted in this paper are the drugs cocaine and 3,4-methylenedioxy-N-methylamphetamine (MDMA or Ecstasy), the explosives TNT and C4, and human remains. Studies include the analysis and identification of the headspace "fingerprint" of a variety of samples, followed by completion of double-blind dog trials of the individual components in an attempt to isolate and understand the target compounds that dogs alert to. SPME–GC/MS has been demonstrated to have a unique capability for the extraction of volatiles from the headspace of forensic specimens including drugs and explosives and shows great potential to aid in the investigation and understanding of the complicated process of canine odor detection. Major variables evaluated for the headspace SPME included fiber chemistry and a variety of sampling times ranging from several hours to several seconds and the resultant effect on ratios of isolated volatile components. For the drug odor studies, the CW/DVB and PDMS SPME fibers proved to be the optimal fiber types. For explosives, the results demonstrated that the best fibers in field and laboratory applications were PDMS and CW/DVB, respectively. Gas chromatography with electron capture detector (GC/ECD) and mass spectrometry (GC/MS) was better for analysis of nitromethane and TNT odors, and C-4 odors, respectively. Field studies with detector dogs have demonstrated possible candidates for new pseudo scents as well as the potential use of controlled permeation devices as non-hazardous training aids providing consistent permeation of target odors.     

Development and validation of a solid-phase microextraction method for the analysis of volatile organic compounds in groundwater samples

Summary Solid-phase microextraction is a relatively recent extraction technique for sample preparation. It has been used successfully to analyse environmental pollutants in a variety of matrices such as soils, water and air. In this work, a simple and rapid method for the analysis of volatile organic and polar compounds from polluted groundwater samples by SPME coupled with gas chromatography (GC) is described. Different types of fibres were studied and the extraction process was optimised. The fibre that proved to be the best to analyse this kind of samples was CAR-PDMS. The method was validated by analysis of synthetic samples and comparison with headspace—GC. The optimised method was successfully applied to the analysis of ground-water samples.     

Use of SPME extraction to determine organophosphorus pesticides adsorption phenomena in water and soil matrices

Solid-phase micro extraction (SPME) coupled with GC enables rapid and simple analysis of organophosphorus pesticides in a range of complex matrices. Investigations were made into the extraction efficiencies from water of six organophosphorus insecticides (methamidophos, omethoate, dimethoate, parathion methyl, malathion, and parathion ethyl) showing a wide range of polarities. Three SPME fibres coated with different stationary phases, polydimethylsiloxane, polyacrylate, and carbowax-divinylbenzene (CW-DVB), were investigated. Water was spiked with the pesticides at concentrations from 1 to 0.01 µg mL-1, and the solutions used for optimization of the procedure. The CW-DVB fibre, with a 65 µm coating, gave the best performance. The optimized experimental conditions were sample volume 10 mL at 20°C, equilibration time 16 min, pH 5, and presence of 10% w/v NaCl. SPME analyses were performed on solutions obtained by equilibrating aqueous pesticide solutions with six certified soils with various physico-chemical characteristics. SPME data were also assessed by comparison with analyses performed by using conventional solid-phase extraction. Results indicate the suitability of SPME for analysis of pesticides in environmental water samples.     

Analysis of volatiles in dehydrated carrot samples by solid-phase microextraction followed by GC-MS

A solid-phase microextraction (SPME)-based method for the GC-MS analysis of volatiles in dehydrated carrot root samples has been developed and the effect of the most important factors (fibre coating, extraction temperature, equilibrium time and extraction time) on the fractionation of different volatiles has been studied. GC-MS chromatograms showed terpenoids relevant to carrot aroma such as alpha-pinene, sabinene, beta-myrcene, limonene, gamma-terpinene, terpinolene, trans-caryophyllene and beta-bisabolene, and several furan derivatives whose origin is discussed in this paper. As an example of application, this methodology has been used for the characterization of volatile composition of industrially dehydrated carrots. SPME followed by GC-MS is shown as an affordable, fast and solvent-free technique which can be performed with low sample amounts and be easily implemented at an industry for quality control purposes.     

Comprehensive two-dimensional gas chromatography, retention indices and time-of-flight mass spectra of flavonoids and chalcones

The applicability of comprehensive two-dimensional gas chromatography (GC×GC) for flavonoids analysis was investigated by separation and identification of flavonoids in standards, and a complex matrix natural sample. The modulation temperature was optimized to achieve the best separation and signal enhancement. The separation pattern of trimethylsilyl (TMS) derivatives of flavonoids was compared on two complementary column sets. Whilst the BPX5/BPX50 (NP/P) column set offers better overall separation, BPX50/BPX5 (P/NP) provides better peak shape and sensitivity. Comparison of the identification power of GC×GC-TOFMS against both the NIST05 MS library and a laboratory (created in-house) TOFMS library was carried out on a flavonoid mixture. The basic retention index information on high-performance capillary columns with a non-polar stationary phase was established and database of mass spectra of trimethylsilyl derivatives of flavonoids was compiled. TOFMS coupled to GC×GC enabled satisfactory identification of flavonoids in complex matrix samples at their LOD over a range of 0.5-10 μg/mL. Detection of all compounds was based on full-scan mass spectra and for each compound a characteristic ion was chosen for further quantification. This study shows that GC×GC-TOFMS yields high specificity for flavonoids derived from real natural samples, dark chocolate, propolis, and chrysanthemum.     

Screening of natural organic volatiles from Prunus mahaleb L. honey: coumarin and vomifoliol as nonspecific biomarkers

Headspace solid-phase microextraction (HS-SPME; PDMS/DVB fibre) and ultrasonic solvent extraction (USE; solvent A: pentane and diethyl ether (1:2 v/v), solvent B: dichloromethane) followed by gas chromatography and mass spectrometry (GC, GC-MS) were used for the analysis of Prunus mahaleb L. honey samples. Screening was focused toward chemical composition of natural organic volatiles to determine if it is useful as a method of determining honey-sourcing. A total of 34 compounds were identified in the headspace and 49 in the extracts that included terpenes, norisoprenoids and benzene derivatives, followed by minor percentages of aliphatic compounds and furan derivatives. High vomifoliol percentages (10.7%-24.2%) in both extracts (dominant in solvent B) and coumarin (0.3%-2.4%) from the extracts (more abundant in solvent A) and headspace (0.9%-1.8%) were considered characteristic for P. mahaleb honey and highlighted as potential nonspecific biomarkers of the honey's botanical origin. In addition, comparison with P. mahaleb flowers, leaves, bark and wood volatiles from our previous research revealed common compounds among norisoprenoids and benzene derivatives.