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.     

Speciation of butyltin compounds in marine sediments with headspace solid phase microextraction and gas chromatography mass spectrometry

A method for the determination of organotin compounds (monobutyl = MBT, dibutyl = DBT, and tributyltin = TBT) in marine sediments by headspace Solid Phase Microextraction (SPME) has been developed. The analytical procedure involved 1) extraction of TBT, DBT and MBT from sediments with HCl and methanol mixture, 2) in situ derivatization with sodium tetraethylborate and 3) headspace SPME extraction using a fiber coated with poly(dimethylsiloxane). The derivatized organotin compounds were desorbed into the splitless injector and simultaneously analyzed by gas chromatography - mass spectrometry. The analytical method was optimized with respect to derivatization reaction and extraction conditions. The detection limits obtained for MBT, DBT and TBT ranged from 730 to 969 pg/g as Sn dry weight. Linear calibration curves were obtained for all analytes in the range of 30-1000 ng/L as Sn. Analysis of a standard reference sediment (CRM 462) demonstrates the suitability of this method for the determination of butyltin compounds in marine sediments. The application to the determination of TBT, DBT and MBT in a coastal marine sediment is shown.     

光皮木瓜果实中香气成分的GC-MS分析

以成熟光皮木瓜为试样,采用顶空固相微萃取与气质联用方法分析检测木瓜果实中的香气成分,共鉴定出43种香气成分,占总峰面积的92.89%。含量较高的依次为2-己烯醛、反式-2-甲基-环戊醇、(E,E)-2,4-己二烯醛、2-丁酮、(Z)-3-己烯醛、醋酸乙酯、(E)-3-己烯-1-醇、茶香螺烷等。其中C6化合物占总量的70%以上,因此可以确定C6化合物是构成光皮木瓜果实清香味的主要成分。     

顶空固相微萃取-气相色谱-质谱法测定小米黄酒风味成分

为全面了解小米黄酒风味成分的构成和气味特征,优化了85μm聚丙烯酸酯(PA)、100μm聚二甲基硅氧烷(PDMS)、75μm碳分子筛(CAR)/PDMS、50/30μm二乙烯基苯(DVB)/CAR/PDMS萃取头提取小米黄酒风味成分的条件,采用顶空固相微萃取(headspace solid phase microextraction,HS-SPME)-气相色谱-质谱法(GC-MS)对风味成分进行定性、定量分析,并计算气味活性值(odor active value,OAV),同时利用OAV分析风味成分的气味特征和气味强度。结果显示:不同萃取头的最优萃取条件为样品量8 mL、萃取时间40 min、萃取温度60℃、NaCl添加量1.5 g。小米黄酒风味成分由醇、酯、含苯化合物、烃、酸、醛、酮、烯、酚和杂环类化合物构成,醇为主要风味成分。通过OAV确定了苯乙醇、苯乙烯、2-甲基萘、1-甲基萘、苯甲醛、苯乙醛、2-甲氧基-苯酚为小米黄酒气味特征成分,苯基乙醇、苯乙醛对气味贡献最大。PA和PDMS萃取头分别对极性和非极性化合物具有较好的吸附效果,CAR/PDMS和DVB/CAR/PDMS萃取头对中等极性化合物具有较好的吸附效果。该研究全面了解了小米黄酒风味成分的构成,为其产品开发及品质控制提供理论了依据。     

Analysis of ethanol and methanol in human body fluids by headspace solid phase microextraction coupled with capillary gas chromatography.

A new method for extraction and analysis of ethanol and methanol in human whole blood, urine and saliva samples based on headspace solid phase microextraction (SPME) using silver sulfide (Ag(2)S) and polyvinyl chloride (PVC) coated on silver wire is described. Unlike commercial fibers, which are coated on fused silica, the proposed fiber has a metallic base to which the coating adheres very strongly. Due to metallic base, this fiber is very durable and is thermally stable up to 250 degrees C. After optimization of coating composition and microextraction conditions, the fiber was used for sampling of methanol and ethanol from human body fluids prior to capillary gas chromatographic analysis. The high recovery (>94%), low detection limits (5.6 mg/L for ethanol and 12.8 mg/L for methanol) and excellent linearity (>0.9900) of calibration graphs made the proposed method suitable for this purpose.     

Determination of bisphenol A in water by isotope dilution headspace solid-phase microextraction and gas chromatography/mass spectrometry without derivatization

The original solid-phase microextraction (SPME) fibers use an epoxy resin adhesive that releases bisphenol A (BPA) during thermal desorption of the fiber. This adversely affects the method detection limit and accuracy when these products are used for the determination of BPA. In this work, 5 new metal alloy SPME fibers that do not use epoxy resins were compared for the extraction of BPA in water. The performance of the optimum SPME fiber with 60 microm carbowax-polyethylene glycol coating for the headspace SPME of BPA in water was investigated systematically under different extraction conditions. Salt was found to increase the partitioning of BPA from water into the headspace until saturation was reached. Partitioning of BPA from water into the headspace also increased at higher extraction temperatures, as did longer extraction times. However, extraction of BPA from water onto the SPME fiber was not improved for solutions adjusted to pH 2 compared to the unadjusted neutral solutions. The new BPA method showed good linearity over the concentration range of 2.5 to 40 microg/L [correlation coefficient (r2) = 0.995] .The method detection limit for BPA was 0.5 microg/L, while the instrument detection limit was as low as 0.05 microg/L. Good repeatability was observed for BPA at levels of 5 and 20 microg/L with relative standard deviation values < 10%. The automated headspace SPME method developed in this work was used to investigate migration of BPA from polycarbonate bottles into water, and levels of BPA in water ranged from 1.7 to 4.1 microg/L.     

Analysis of total propionic acid in feed using headspace solid-phase microextraction and gas chromatography

A method is described to analyze total propionic acid content (free propionic acid + sodium, ammonium, calcium salts, etc.) in feed, using headspace solid-phase microextraction (HS-SPME) of a feed suspension in salted and acidified water. Optimization of the extraction variables was done by simplex method after choosing a polyacrilate fiber to enhance the response of this acid. Separation was made by capillary gas chromatography (GC), using a special free fatty acid phase (FFAP) column for acids and a flame ionization detector (FID). Some of the chromatograms were also done, injecting the SPME fiber in a GC-mass spectrometry (MS) system, working with some specific ions for propionic acid, to be selective enough to avoid confusing the propionic acid peak with interferences of those complex matrixes. The method was tested for linearity and repeatability. Detection and quantification limits were also calculated. The method was applied to commercial feed samples, very variable in composition, quantifying by standard addition method. No major interferences were observed.     

Identification of potent odourants in wine and brewed coffee using gas chromatography-olfactometry and comprehensive two-dimensional gas chromatography

Volatile constituents in wine and brewed coffee were analyzed using a combined system incorporating both GC-olfactometry (GC-O) and comprehensive two-dimensional GC-flame ionization detection (GC×GC-FID). A column set consisting of a 15m first dimension ((1)D; DB-FFAP (free fatty acid phase)), and a 1.0m (2)D column (DB-5 phase) was applied to achieve the GC×GC separation of the volatile extracts isolated by using solid phase extraction (SPE). While 1D GC resulted in many overlapping peaks, GC×GC allowed resolution of co-eluting compounds which coincided with the odour region located using GC-O. Character-impact odourants were tentatively identified through data correlation of GC×GC contour plots across results obtained using either time-of-flight mass spectrometry (TOFMS), or with flame photometric detection (FPD) for sulfur speciation. The odourants 2-methyl-2-butenal, 2-(methoxymethyl)-furan, dimethyl trisulfide, 2-ethyl-5-methyl-pyrazine, 2-octenal, 2-furancarboxaldehyde, 3-mercapto-3-methyl-1-butanol, 2-methoxy-3-(2-methylpropyl)-pyrazine, 2-furanmethanol and isovaleric acid were suspected to be particularly responsible for coffee aroma using this approach. The presented methodology was applied to identify the potent odourants in two different Australian wine varietals. 1-Octen-3-ol, butanoic acid and 2-methylbutanoic acid were detected in both Merlot and a Sauvignon Blanc+Semillon (SV) blend with high aroma potency. Several co-eluting peaks of ethyl 4-oxo-pentanoate, 3,7-dimethyl-1,5,7-octatrien-3-ol, (Z)-2-octen-1-ol, 5-hydroxy-2-methyl-1,3-dioxane were likely contributors to the Merlot wine aroma; while (Z)-3-hexen-1-ol, β-phenylethyl acetate, hexanoic acid and co-eluting peaks of 3-ethoxy-1-propanol and hexyl formate may contribute to SV wine aroma character. The volatile sulfur compound 2-mercapto-ethyl acetate was believed to contribute a fruity, brothy, meaty, sulfur odour to Australian Merlot and SV wines.     

Determination of organotin compounds in-water by headspace solid phase microextraction with gas chromatography-mass spectrometry

This investigation evaluates headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS) to determine trace levels of organotins in water. The organotins were derivatized in situ with sodium tetraethylborate and adsorbed on a poly(dimethysiloxane) (PDMS)-coated fused silica fiber. The SPME experimental procedures to extract organotins in water were at pH 5, with extraction and derivatization simultaneously at 45 degrees C for 30 min in a 2% sodium tetraethylborate solution and a sample solution volume in the ratio of 1:1, and desorption in the splitless injection port of the GC at 260 degrees C for 2 min. Detection limits are determined to be in the low ng/L range. According to the analysis, the linearity range is from 10 to 10,000 ng/L with R.S.D. values below 12% except triphenyltin (24%). The proposed method was tested by analyzing surface seawater from the harbors on the Taiwanese coast for organotins residues. Some organotins studied were detected in the analyzed samples. Results of this study demonstrate the adequacy of the headspace SPME-GC-MS method for analyzing organotins in sea water samples.     

顶空固相微萃取-全二维气相色谱/飞行时间质谱法分析闽南乌龙茶中的挥发性成分及其在分类中的应用

采用顶空固相微萃取(HS-SPME)结合全二维气相色谱/飞行时间质谱(GC×GC-TOF MS)分析了闽南乌龙茶中的挥发性成分。从48份不同等级和产季的乌龙茶(铁观音、黄金桂、本山、毛蟹和梅占)中获得了2000余种挥发性化合物,经筛选得到51种共有组分,并结合质谱数据库、保留指数与结构谱图等进行了初步鉴定。在此基础上采用主成分分析法(PCA)获得得分投影图,直观给出了不同样品的分类趋势。通过逐步判别获得9种对分类结果有显著影响的组分,并以此为变量通过Fisher判别法(FDA)建立了4个判别函数,对样品的分类准确率达到97.9%。本试验证实了以挥发性成分识别闽南乌龙茶的可行性。     

Simultaneous analysis of polychlorinated biphenyls and polychlorinated naphthalenes by isotope dilution comprehensive two-dimensional gas chromatography high-resolution time-of-flight mass spectrometry

Polychlorinated biphenyls (PCBs) and polychlorinated naphthalenes (PCNs) are listed as persistent organic pollutants (POPs) under the Stockholm Convention. Because they have similar physical and chemical properties, they are coeluted and are usually analyzed separately by different gas chromatography high-resolution mass spectrometry (GC-HRMS) methods. In this study, a novel method was developed for simultaneous analysis of six indicator PCBs, 12 dioxin-like PCBs, and 16 PCNs using isotope dilution comprehensive two-dimensional gas chromatography with high-resolution time-of-flight mass spectrometry (GC × GC-HRTOF-MS). The method parameters, including the type of GC column, oven temperature program, and modulation period, were systematically optimized. Complete separation of all target analytes and the matrix was achieved with a DB-XLB column in the first dimension and a BPX-70 column in the second dimension. The isotope dilution method was used for quantification of the PCBs and PCNs by GC × GC-HRTOF-MS. The method showed good linearity from 5 to 500 pg μL⁻¹ for all the target compounds. The instrumental limit of detection ranged from 0.03 to 0.3 pg μL⁻¹ for the 18 PCB congeners and from 0.09 to 0.6 pg μL⁻¹ for the 16 PCN congeners. Repeatability for triplicate injections was always lower than 20%. The method was successfully applied to the determination of 18 PCBs present at 0.9–2054 pg g⁻¹ and 16 PCNs present at 0.2–15.7 pg g⁻¹ in three species of fish. The GC × GC-HRTOF-MS results agreed with those obtained by GC-HRMS. The GC × GC-HRTOF-MS method proved to be a sensitive and accurate technique for simultaneous analysis of the selected PCBs and PCNs. With the excellent chromatographic separation offered by GC × GC and accurate mass measurements offered by HRTOF-MS, this method allowed identification of non-target contaminants in the fish samples, including organochlorine pesticides and polycyclic aromatic hydrocarbons.     

Determination of ethylphenol compounds in wine by headspace solid-phase microextraction in conjunction with gas chromatography and flame ionization detection

Headspace solid phase microextraction (HS-SPME) was investigated as a solvent-free alternative method for the extraction and determination of 4-ethylphenol (EP) and 4-ethylguaiacol (EG) in red wine by capillary gas chromatography with flame ionization detection (FID) and compared to liquid-liquid extraction.For HS-SPME, better results were obtained with saturated sodium chloride samples, at 55 °C, using a 85 μm polyacrylate fiber. An absorption time of 40 min was needed to reach the absorption equilibrium for EG. This 40-min duration corresponds to the beginning of EP equilibrium and was selected for the experiments. In these conditions, the calibration graphs were linear in the range 5-5000 μg l⁻¹ and the sensitivity was nearly the same for the two compounds. The detection limits were in the low μg l⁻¹ range. In model wine solutions, result obtained with the liquid-liquid extraction method exhibit a linear calibration between 25 and 10,000 μg l⁻¹ with a detection limit of 1 μg l⁻¹, but, the relative standard deviations of the EP and EG result in the low concentration range (<50 μg l⁻¹) are higher than those obtained by HS-SPME (15% compared to 2% for EP and 12% compared to 5% for EG). Taking into account the numerous volatile compounds in wine, HS-SPME is a rapid and valid alternative technique for use in the determination of ethylphenols at trace levels.     

Analysis of nitromethane from samples exposed in vitro to chloropicrin by stable isotope dilution headspace gas chromatography with mass spectrometry

Chloropicrin (trichloronitromethane) is a widely used soil fumigant and an old chemical warfare agent. The metabolism of chloropicrin is not well known in mammals but nitromethane has been shown to be one of its main metabolites. Here, a fast and simple headspace gas chromatography with mass spectrometry method was applied for the measurement of nitromethane from aqueous samples. The analytical method was validated using stable isotope labeled internal standard and a small sample volume of 260 μL. No conventional sample preparation steps were needed. The method was accurate (relative standard deviations ≤1.5%) and linear (R² = 0.9996) within the concentration range of 0.1?6.0 μg/mL. This method was used to measure nitromethane in in vitro incubations with human and pig liver cell fractions containing enzymes for xenobiotic metabolism, exposed to chloropicrin. The results indicate that the presence of glutathione is necessary for the formation of nitromethane from chloropicrin. Also, nitromethane was formed mostly in liver cytosol fractions, but not in microsomal fractions after the incubation with chloropicrin. Our results suggest that although nitromethane is not the unequivocal biomarker of chloropicrin exposure, this method could be applied for screening the elevated levels in humans after chloropicrin exposure.     

Analysis of anatoxin-a in biological samples using liquid chromatography with fluorescence detection after solid phase extraction and solid phase microextraction

Anatoxin-a is a naturally occurring, potent neurotoxin produced by some species of cyanobacteria in freshwaters. This toxin, which is a potential health hazard, especially to animals, has been determined in different biological matrices such as several cyanobacterial cultures and water samples and carps and mussels tissue using a sensitive High Performance Liquid Chromatography with Fluorescence detection method. Sonication was the technique selected for the extraction of intracellular anatoxin-a and solid phase extraction using weak cation exchange was used for the concentration and purification of the samples. 4-Fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F) was used to convert anatoxin into a highly fluorescent derivative. Recovery experiments were performed for each type of matrix used in this work, and adequate values were obtained (71-87%). Limits of detection for anatoxin-a were estimated to be in the ng/L and ng/g level for water and cyanobacterial samples, respectively. The results obtained were also compared with those obtained after using solid phase microextraction, as an alternative for the extraction and purification of the samples. Advantages and disadvantages regarding to the efficiency for impurities removal, simplicity and rapidity and the potential for concentration enhancement of using both methodologies have been also discussed.     

Analysis of organic compounds in environmental samples by headspace solid phase microextraction

The analysis of samples contaminated by organic compounds is an important aspect of environmental monitoring. Because of the complex nature of these samples, isolating target organic compounds from their matrices is a major challenge. A new isolation technique, solid phase microextraction, or SPME, has recently been developed in our laboratory. This technique combines the extraction and concentration processes into one step; a fused silica fiber coated with a polymer is used to extract analytes and transfer them into a GC injector for thermal desorption and analysis. It is simple, rapid, inexpensive, completely solvent-free, and easily automated. To minimize matrix interferences in environmental samples, SPME can be used to extract analytes from the headspace above the sample. The combination of headspace sampling with SPME separates volatile and semi-volatile analytes from non-volatile compounds, thus greatly reducing the interferences from non-target compounds. This paper reports the use of headspace SPME to isolate volatile organic compounds from various matrices such as water, sand, clay, and sludge. By use of the technique, benzene, toluene, ethyl-benzene, and xylene isomers (commonly known as BTEX), and volatile chlorinated compounds can be efficiently isolated from various matrices with good precision and low limits of detection. This study has found that the sensitivity of the method can be greatly improved by the addition of salt to water samples, water to soil samples, or by heating. Headspace SPME can also be used to sample semi-volatile compounds, such as PAHs, from complex matrices.     

Application of headspace solid phase microextraction and gas chromatography to the screening of volatile compounds from some Brazilian aromatic plants

Summary An HS-SPME method was developed and applied for the isolation of volatile organic compounds from plants native or acclimatized to Brazil. Method optimization was performed using typical analytes from the target samples; fibers coated with 100 μm PDMS and 75 μm Carboxen/PDMS were tested. Using PDMS 100 μm fibers and GC-MS for separation and identification, up to 99.9% of the peak area in the chromatograms from plants were identified. The method was also applied to quantify the major volatile components of one of the samples (Aloysia gratissima) with results comparable to those from the conventional steam distillation method.     

Quantification of chloroanisoles in cork using headspace solid-phase microextraction and gas chromatography with electron capture detection

Chloroanisoles can migrate from the cork stopper in wine bottles to the wine and give it a musty taint so it is important to find a method by which they can be determined. The aim of this paper is to develop a method for quantifying 2,4-dichloroanisole, 2,6-dichloroanisole, 2,4,6-trichloroanisole, 2,3,4,6-tetrachloroanisole and 2,3,4,5,6-pentachloroanisole in cork using headspace solid-phase microextraction and gas chromatography with electron capture detection. After we had prepared the cork standards that were so essential to the work we optimised the parameters that most influence headspace solid-phase microextraction: fibre coating, vial volume, cork, kind and volume of solvent to help the extraction, extraction temperature and time, ionic strength and stirring. The method quantifies the total amount of chloroanisoles in cork stoppers (natural, agglomerated, agglomerated with disks and sparkling wine stoppers), at suitable concentrations so that the capacity of these compounds to give wine a musty taint can be evaluated. The quantification limits are: 2,6-dichloroanisole (8.6 ng/g), 2,4,6-trichloroanisole (0.8 ng/g), 2,4-dichloroanisole (3.5 ng/g), 2,3,4,6-tetrachloroanisole (0.6 ng/g), 2,3,4,5,6-pentachloroanisole (0.8 ng/g). The other quality parameters are: recoveries (90.3-105.8%), repeatability (4-13% (RSD expressed)) and intermediate precision (5-14% (RSD expressed)).     

Determination of aliphatic amines in water by gas chromatography using headspace solvent microextraction

The possibility of applying headspace microextraction into a single drop for the determination of amines in aqueous solutions is demonstrated. A 1 μl drop of benzyl alcohol containing 2-butanone as an internal standard was suspended from the tip of a micro syringe needle over the headspace of stirred sample solutions for extraction. The drop was then injected directly into a GC. The total chromatographic determination was less than 10 min. Optimization of experimental conditions (sampling time, sampling temperature, stirring rate, ionic strength of the solution, concentration of reagents, time of extraction and organic drop volume) with respect to the extraction efficiency were investigated and the linear range and the precision were also examined. Calibration curves yielded good linearity and concentrations down to 2.5 ng ml⁻¹ were detectable with R.S.D. values ranging from 6.0 to 12.0%. Finally, the method was successfully applied to the extraction and determination of amines in tap and river water samples. This system represents an inexpensive, fast, simple and precise sample cleanup and preconcentration method for the determination of volatile organic compounds at trace levels.     

SPME-GC联用测定环境水样中的酚类化合物

建立了固相微萃取与气相色谱联用技术测定环境水样中酚类化合物的方法. 探讨了pH、离子强度、萃取头类型、萃取时间以及解析时间等条件对酚类化合物萃取量的影响, 优化了GC仪器条件. 在优化的条件下, 酚类化合物的响应值与浓度有良好的线性关系, 线性范围为0.20～200 μg/L, 检出限在0.019～0.10 μg/L之间, 相对标准偏差(RSD, n=5)为4.4%～11%, 水样平均加标回收率为92.2%～101.9%, 所建立的方法可测定环境水样中的酚类化合物.