Simultaneous determination of unmodified sevoflurane and of its metabolite hexafluoroisopropanol in urine by headspace sorptive extraction-thermal desorption-capillary gas chromatography-mass spectrometry

Unmodified sevoflurane and its metabolite, hexafluoroisopropanol (HFIP), have both been proposed as biomarkers of exposure in post-shift urine for operating room personnel exposed to inhalation anaesthetic sevoflurane. We used headspace sorptive extraction (HSSE) and thermal desorption-capillary GC-MS to assess sensitively both compounds in the urine matrix (after a HFIP deconjugation step). In GC-MS splitless mode, calibration plots (approximately 15-650 microg/L) were linear (r2 > 0.9910) and the limits of detection (1 microg/L for both biomarkers) showed increased sensitivity for HFIP with respect to the previously described headspace GC-MS method. The method was suitable for biological monitoring of both biomarkers of exposure to sevoflurane.     

Impact of phase ratio, polydimethylsiloxane volume and size, and sampling temperature and time on headspace sorptive extraction recovery of some volatile compounds in the essential oil field

This study evaluates concentration capability of headspace sorptive extraction (HSSE) and the influence of sampling conditions on HSSE recovery of an analyte. A standard mixture in water of six high-to-medium volatility analytes (isobutyl methyl ketone, 3-hexanol, isoamyl acetate, 1,8-cineole, linalool and carvone) was used to sample the headspace by HSSE with stir bars coated with different polydimethylsiloxane (PDMS) volumes (20, 40, 55 and 110 microL, respectively), headspace vial volumes (8, 21.2, 40, 250 and 1000 mL), sampling temperatures (25, 50 and 75 degrees C) and sampling times (30, 60 and 120 min, and 4, 8 and 16 h). The concentration factors (CFs) of HSSE versus static headspace (S-HS) were also determined. Analytes sampled by the PDMS stir bars were recovered by thermal desorption (TDS) and analysed by capillary GC-MS. This study demonstrates how analyte recovery depends on its physico-chemical characteristics and affinity for PDMS (octanol-water partition coefficients), sampling temperatures (50 degrees C) and times (60 min), the volumes of headspace (40 mL) and of PDMS (in particular, for high volatility analytes). HSSE is also shown to be very effective for trace analysis. The HSSE CFs calculated versus S-HS with a 1000 mL headspace volumes at 25 degrees C during 4 h sampling ranged between 10(3) and 10(4) times for all analytes investigated while the limits of quantitation determined under the same conditions were in the nmol/L range.     

Quantitative analysis of perfumes in talcum powder by using headspace sorptive extraction

Quantitative analysis of perfume dosage in talcum powder has been a challenge due to interference of the matrix and has so far not been widely reported. In this study, headspace sorptive extraction (HSSE) was validated as a solventless sample preparation method for the extraction and enrichment of perfume raw materials from talcum powder. Sample enrichment is performed on a thick film of poly(dimethylsiloxane) (PDMS) coated onto a magnetic stir bar incorporated in a glass jacket. Sampling is done by placing the PDMS stir bar in the headspace vial by using a holder. The stir bar is then thermally desorbed online with capillary gas chromatography-mass spectrometry. The HSSE method is based on the same principles as headspace solid-phase microextraction (HS-SPME). Nevertheless, a relatively larger amount of extracting phase is coated on the stir bar as compared to SPME. Sample amount and extraction time were optimized in this study. The method has shown good repeatability (with relative standard deviation no higher than 12.5%) and excellent linearity with correlation coefficients above 0.99 for all analytes. The method was also successfully applied in the quantitative analysis of talcum powder spiked with perfume at different dosages.     

Automated headspace solid-phase dynamic extraction to analyse the volatile fraction of food matrices

High concentration capacity headspace techniques (headspace solid-phase microextraction (HS-SPME) and headspace sorptive extraction (HSSE)) are a bridge between static and dynamic headspace, since they give high concentration factors as does dynamic headspace (D-HS), and are as easy to apply and as reproducible as static headspace (S-HS). In 2000, Chromtech (Idstein, Germany) introduced an inside-needle technique for vapour and liquid sampling, solid-phase dynamic extraction (SPDE), also known as "the magic needle". In SPDE, analytes are concentrated on a 50 microm film of polydimethylsiloxane (PDMS) and activated carbon (10%) coated onto the inside wall of the stainless steel needle (5 cm) of a 2.5 ml gas tight syringe. When SPDE is used for headspace sampling (HS-SPDE), a fixed volume of the headspace of the sample under investigation is sucked up an appropriate number of times with the gas tight syringe and an analyte amount suitable for a reliable GC or GC-MS analysis accumulates in the polymer coating the needle wall. This article describes the preliminary results of both a study on the optimisation of sampling parameters conditioning HS-SPDE recovery, through the analysis of a standard mixture of highly volatile compounds (beta-pinene, isoamyl acetate and linalool) and of the HS-SPDE-GC-MS analyses of aromatic plants and food matrices. This study shows that HS-SPDE is a successful technique for HS-sampling with high concentration capability, good repeatability and intermediate precision, also when it is compared to HS-SPME.     

A survey on high-concentration-capability headspace sampling techniques in the analysis of flavors and fragrances

This survey critically discusses high-concentration-capacity (HCC) headspace (HS) techniques applied to sample the volatile fraction of matrices of interest in the flavors and fragrance fields. In particular, the advantages, limits, and fields of application of HS solid-phase microextraction (SPME), high-capacity HS sorptive extraction (HSSE) and HS solid-phase dynamic extraction (SPDE) are evaluated. These techniques are discussed in view of the peculiar characteristic of HCC-HS techniques, from the standpoint that these techniques are a bridge between static (S-HS) and dynamic HS (D-HS) because they are as simple, fast, easy to automate, and reliable as S-HS, yet afford analyte concentration factors comparable to those of D-HS. Moreover, the different degree of their development is a consequence of the different times in which they were introduced into the market, because the potential of HS-SPME is now well known, having been introduced approximately 12 years ago, but that of HSSE has still to be fully explored, and HS-SPDE still has to be investigated because it is very recent.     

Headspace sampling of the volatile fraction of vegetable matrices

The evolution of vapour phase sampling of the volatile fraction of vegetable matrices, or of products directly related to them, over the period 1996-2007 is reviewed. High concentration capacity headspace (HCC-HS) and dynamic headspace (D-HS) techniques, that is headspace sampling approaches where the analytes in the vapour phase are concentrated into a sorbent, an adsorbent or a solvent, are considered. Advantages, disadvantages and applications to the vegetable field of several successful techniques based on these approaches are critically presented, including in-tube sorptive extraction (INCAT, HS-SPDE), headspace sorptive extraction (HSSE), solid-phase aroma concentrate extraction (SPACE), large surface area HCC-HS sampling (MESI, MME, HS-STE), headspace liquid-phase microextraction (HS-LPME) and dynamic headspace samplings (D-HS). The developments necessary to overcome some of the limits of the above approaches and techniques are also discussed in view of their application to new fields.     

Dynamic headspace analysis of solid waste materials

A dynamic headspace stripping technique for the extraction of volatile organic compounds has been applied to a variety of solid and semisolid waste materials. A simple glass apparatus accommodates a wide range of sample sizes and allows for the volatiles to be stripped at elevated temperatures. Concentration on Tenax, followed by thermal desorption and analysis by fused silica capillary gas chromatography provides detailed information on the volatile content of waste samples of widely differing matrix composition.     

顶空吸附萃取-气相色谱法分析小麦中部分风味物质

采用顶空吸附萃取法(headspace sorptive extraction, HSSE)建立了小麦中部分风味物质的分析方法。以硅橡胶为原料,采用溶胶-热空气硫化法,在模具中定型制得硅橡胶萃取棒。萃取棒的硅橡胶层体积约为87 μL,热稳定性好,耐热温度达到390 ℃。萃取棒吸附的风味物质经自制热解吸装置热脱附,被吹扫进入气相色谱仪进行分析。考察了萃取温度及时间、相比、热解吸条件对该方法萃取效率的影响。在优化条件下分析小麦粉标准样品,结果表明:方法的线性关系良好(r>0.9979),检出限为0.09～1.00 μg/kg,标准物质的平均添加回收率为95%～121%,相对标准偏差在2.2%～7.8%之间。对小麦粉实际样品进行分析,采用外标法得到了7种风味物质的绝对含量。该方法简便快捷,检出限低,适用于小麦中风味物质的快速定量分析。     

Influence of polydimethylsiloxane outer coating and packing material on analyte recovery in dual-phase headspace sorptive extraction

Dual phase twisters (DP twisters), consisting of a polydimethylsiloxane (PDMS) outer coating and a second complementary (ad)sorbent as inner packing, have recently been shown to extend the applicability of headspace sorptive extraction (HSSE). In comparison to HSSE using PDMS only, the recovery of analytes from the headspace of a solid or liquid matrix is increased by combining the concentration capabilities of two sampling materials operating on different mechanisms (sorption and adsorption). This study compares the performance of DP twisters consisting of different PDMS outer coatings and different packing materials, including Tenax GC, a bisphenol-PDMS copolymer, Carbopack coated with 5% of Carbowax and beta-cyclodextrin, for the analysis of the headspace of roasted Arabica coffee, dried sage leaves and an aqueous test mixture containing compounds with different water solubility, acidity, polarity and volatility as test samples. In general, DP twisters showed a higher concentration capability than the corresponding conventional PDMS twisters for the analytes considered. The highest recoveries were obtained with DP twisters consisting of 0.2mm thick PDMS coating combined with Tenax GC, a bisphenol-PDMS copolymer and Carbopack coated with 5% of Carbowax as inner adsorption phase.     

Non-destructive method to determine halophenols and haloanisoles in cork stoppers by headspace sorptive extraction

The new solvent-free technique called headspace sorptive extraction (HSSE) was used to determine 2,4,6-trichlorophenol, 2,3,4,6-tetrachlorophenol, 2,4,6-trichloroanisole, 2,3,4,6-tetrachloroanisole, 2,4,6-tribromoanisole, pentachloroanisole in cork stoppers, without grinding them, as these may be responsible for the cork taint off-flavour in wine. The best HSSE sorption kinetics for the target analytes were obtained after submitting the spiked corks to 100 degrees C for 1h, followed by a 30 min stabilization time at room temperature. The stir bar was desorbed in a thermal desorption system coupled to a gas chromatograph-mass spectrometer. The method proposed showed good linearity over the concentration range tested, 1-70 ngg(-1), and correlation coefficients ranged from 0.90 to 0.99 for all the analytes. The reproducibility and repeatability of the method were estimated between 4.91 and 12.67%. The effect of the different cork matrixes on the extraction recovery of the target compounds was studied, with the natural corks showing the higher recovery percentage in relation to agglomerate ones.     

Development of a sensitive non-targeted method for characterizing the wine volatile profile using headspace solid-phase microextraction comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry

Future understanding of differences in the composition and sensory attributes of wines require improved analytical methods which allow the monitoring of a large number of volatiles including those present at low concentrations. This study presents the optimization and application of a headspace solid-phase microextraction (HS-SPME) method for analysis of wine volatiles by comprehensive two-dimensional gas chromatography (GC×GC) time-of-flight mass spectrometry (TOFMS). This study demonstrates an important advancement in wine volatile analysis as the method allows for the simultaneous analysis of a significantly larger number of compounds found in the wine headspace compared to other current single dimensional GC-MS methodologies. The methodology allowed for the simultaneous analysis of over 350 different tentatively identified volatile and semi-volatile compounds found in the wine headspace. These included potent aroma compound classes such as monoterpenes, norisoprenoids, sesquiterpenes, and alkyl-methoxypyrazines which have been documented to contribute to wine aroma. It is intended that wine aroma research and wine sensory research will utilize this non-targeted method to assess compositional differences in the wine volatile profile.     

Comparison of four extraction methods for analysis of volatile hop‐derived aroma compounds in beer

The volatile organic compound profile in beer is derived from hops, malt, yeast, and interactions between the ingredients, making it very diverse and complex. Due to the range and diversity of the volatile organic compounds present, the choice of the extraction method is extremely important for optimal sensitivity and selectivity. This study compared four extraction methods for hop‐derived compounds in beer late hopped with Nelson Sauvin. Extraction capacity and variation were compared for headspace solid‐phase micro extraction, stir bar sorptive extraction, headspace sorptive extraction, and solvent‐assisted flavor evaporation. Generally, stir bar sorptive extraction was better suited for acids, headspace sorptive extraction for esters and aldehydes, while headspace solid‐phase microextraction was less sensitive overall, extracting 40% fewer compounds. Solvent‐assisted flavor evaporation with dichloromethane was not suitable for the extraction of hop‐derived volatile organic compounds in beer, as the profile was strongly skewed towards alcohols and acids. Overall, headspace sorptive extraction is found to be best suited, closely followed by stir bar sorptive extraction.     

Preparation of sol-gel polyethylene glycol-polydimethylsiloxane-poly(vinyl alcohol)-coated sorptive bar for the determination of organic sulfur compounds in water

A novel headspace sorptive extraction (HSSE) using a glass bar coated with carbowax (polyethylene glycol)-polydimethylsiloxane-poly(vinyl alcohol) (CW/PDMS/PVA) prepared by sol-gel technology method was proposed for the determination of volatile organic sulfur compounds (VOSs) in water. After the extraction, the sorptive bar was desorbed with 60 microL of ethanol and 30 microL of the extract was analysed by large volume injection (LVI) into a gas chromatography-flame photometric detector (GC-FPD). The parameters affecting the headspace sorptive extraction of VOSs such as extraction and desorption time, extraction temperature, stirring speed, desorption solvent, headspace phase ratio, salt and pH were carefully investigated and the optimized experimental conditions were established. The limits of detection (LODs) for the studied VOSs ranged from 0.04 to 4.8 microg/L with the relative standard deviations (RSDs) ranging from 4.5 to 10.2% (n=6). The reproducibility for the preparation of CW/PDMS/PVA-coated sorptive bar ranged from 3.2 to 9.2% in one batch, and from 2.8 to 18.5% in batch-to-batch, and more than 50 extractions can be achieved without apparent loss. The proposed method was compared with polydimethylsiloxane-HSSE and carboxen/PDMS-headspace-solid phase microextraction (CAR/PDMS-HS-SPME) under their optimum conditions, CW/PDMS/PVA-HSSE shows the highest adsorption capacity (larger surface area and more active sites), the highest sensitivity (about 10 times) and the best polarity matching for VOSs.     

Determination of polydimethylsiloxane-air partition coefficients using headspace sorptive extraction

Polydimethylsiloxane-air partition coefficients (K(PDMS-A)) were determined using direct headspace analysis and headspace sorptive extraction (HSSE) with polydimethylsiloxane-coated (PDMS) stir bars. The partition coefficients were investigated for three compounds, p-dichlorobenzene (PDCB), naphthalene and camphor, all of which sublimate at room temperature and find use as moth repellents. In order to determine the K(PDMS-A) values of these compounds, the air concentration and the concentration present on PDMS, both at equilibrium, were measured. The results indicate that PDMS-air partition coefficients are proportional to octanol-air partition coefficients. Thus, the latter could be used to estimate the extraction efficiency of PDMS for these compounds in air. Alternatively, octanol-air partition coefficients for organic compounds could be estimated from the PDMS-air partition coefficient values. As expected, the PDMS-air (or octanol-air) partition coefficient increased with decreasing temperature. Importantly, the partition coefficients determined at saturated vapor pressures were lower than the values determined at lower analyte concentrations, with the differences being greater for compounds with larger partition coefficients. Consequently, caution should be exercised when applying K(PDMS-A) values determined at high analyte concentrations to measurements at lower concentrations, especially when the partition coefficients are large.     

Suitability of polydimethylsiloxane rods for the headspace sorptive extraction of polybrominated diphenyl ethers from water samples

The suitability of an inexpensive polydimethysiloxane (PDMS) sorbent, produced on an industrial scale, for the extraction of polybrominated diphenyl ethers (PBDEs), from tetra- to hexabrominated congeners, from water samples was assessed. Experiments were carried out using samples spiked with a pentabromo diphenyl ether (pentaBDE) mixture, PDMS rods with a diameter of 2 mm and gas chromatography with micro-electron-capture detection (GC-micro-ECD). Influence of several variables on the efficiency of the enrichment step and the further desorption of the analytes was investigated in detail. The best performance was achieved in the headspace sorptive extraction (HSSE) mode, at 95 degrees C, using 80 mL water samples containing a 30% of sodium chloride. Extractions were performed overnight using disposable PDMS rods with a length of 10 mm (31 microL volume). Analytes were further recovered from the PDMS sorbent using just 1 mL of diethyl ether. This solvent was evaporated and extracts reconstituted with 25 microL of isooctane. Under final working conditions absolute extraction efficiencies from 69 to 93% and enrichment factors higher than 2200 folds were achieved for all species. The proposed method provided acceptable precisions (relative standard deviations values under 12%), correlation coefficients higher than 0.998 and the yield of the HSSE process remained constant for different water samples.     

顶空气相色谱-质谱联用技术的应用进展

顶空分析作为一种无有机溶剂萃取的样品处理技术,通常与气相色谱-质谱（GC-MS）技术结合用来分析复杂基质中的挥发性有机物。顶空气相色谱-质谱（HS-GC-MS）技术具有快速、高效、环保、灵敏度高等特点,在常规分析中发挥着重要作用。该文简要概述了静态顶空、动态顶空、顶空固相微萃取分析以及GC-MS联用技术,并介绍了整个顶空分析系统的影响因素和优化过程。根据基质类型的分类,综述了HS-GC-MS在食品和饮料、环境、生物等样品中的应用实例。HS-GC-MS的研究非常活跃,不断出现新应用,在分析挥发性有机物方面具有广阔前景。     

Analysis of the headspace of foodstuffs near room temperature

Formation of volatiles in onion varieties, aging of coffee, and the quality of birch syrup were studied by using near room temperature headspace GC-MS analysis. Accurate volumes (1–500 mL) of the gaseous samples were introduced into the capillary column either by a syringe or by sucking with a pump. The standard deviation of the contents was typically 1-7% depending on the foodstuff and the compound. The ratio of 2,3-butanedione to 2-methylfuran decreased during the storage of coffee and was a typical measure of aging. Analysis of even the very polar 2,5-dimethyl-4-hydroxy-3(2H)-furanone in the headspace of birch syrup was possible. The distribution patterns of the sulfur-containing volatiles generated by crushed onions were close to each other in different varieties. The rate of the total formation of the compounds varied from cultivar to cultivar.     

Aristolochene synthase: mechanistic analysis of active site residues by site-directed mutagenesis

Incubation of farnesyl diphosphate (1) with Penicillium roqueforti aristolochene synthase yielded (+)-aristolochene (4), accompanied by minor quantities of the proposed intermediate (S)-(-)germacrene A (2) and the side-product (-)-valencene (5) in a 94:4:2 ratio. By contrast, the closely related aristolochene synthase from Aspergillus terreus cyclized farnesyl diphosphate only to (+)-aristolochene (4). Site-directed mutagenesis of amino acid residues in two highly conserved Mg(2+)-binding domains led in most cases to reductions in both k(cat) and k(cat)/K(m) as well as increases in the proportion of (S)-(-)germacrene A (2), with the E252Q mutant of the P. roqueforti aristolochene synthase producing only (-)-2. The P. roqueforti D115N, N244L, and S248A/E252D mutants were inactive, as was the A. terreus mutant E227Q. The P. roqueforti mutant Y92F displayed a 100-fold reduction in k(cat) that was offset by a 50-fold decrease in K(m), resulting in a relatively minor 2-fold decrease in catalytic efficiency, k(cat)/K(m). The finding that Y92F produced (+)-aristolochene (4) as 81% of the product, accompanied by 7% 5 and 12% 2, rules out Tyr-92 as the active site Lewis acid that is responsible for protonation of the germacrene A intermediate in the formation of aristolochene (4).     

Analysis of volatile organic compounds in polymers by dynamic headspace and gas chromatography/mass spectrometry

An experimental method for the analysis of volatile organic compounds in polymers is described. The technique involves dynamic headspace sampling, collection, and concentration of the volatiles in a cold trap, followed by capillary column gas chromatography/mass spectometry. Flow switching is carried out by the Deans switching technique. Four technical polymers used as pharmaceutical packaging materials have been analyzed in order to demonstrate the method.     

Coupling of Dynamic Headspace Sampling and Solid Phase Microextraction

A simple lab-made apparatus allowing the use of a SPME fiber as sorptive device for isolation of analytes from varied samples using dynamic headspace sampling (DHS) is presented here. The principal parameters for the operation of this device - the extraction time and the flow of purging gas - were studied using aqueous test solutions of volatile and semi-volatile analytes. Compared to conventional HS-SPME, DHS-SPME provided a substantial reduction in the extraction time with linearity, accuracy and precision comparable to the conventional approach. For a complex matrix such as mango pulp, the extraction efficiency of volatiles using the DHS-SPME combination was up to six times higher than that of conventional HS-SPME.