Static Headspace Sampling Research Articles

Profiles of volatile compounds and sensory analysis of three blends of coffee: influence of different proportions of Arabica and Robusta and influence of roasting coffee with sugar

AbstractOne hundred and forty‐six volatile compounds were identified and quantified using a static headspace sampler in three blends of coffee: Arabica/Robusta 80:20 (A80:R20) natural roasted coffee, Arabica/Robusta 20:80 (A20:R80) natural roasted coffee and Arabica/Robusta 20:80 with 50% of Robusta coffee roasted with sugar (A20:R80 50% Torrefacto). The different proportion of Arabica and Robusta coffee in the blend A80:R20 versus A20:R80 influenced the amounts of 20 chemical families of volatile compounds. Aldehydes, ketones, alcohols, pyrroles, pyrazines, furans, thiazoles, thiophenes, esters, oxazoles, lactones, sulphur compounds, pyridines, alkanes, alkenes, phenolic compounds, benzenic compounds, acids, pyranones and terpenes were present in higher quantities in the sample containing 80% of Arabica coffee, whereas sulphur compounds were more abundant in the coffee with 80% of Robusta. Sensory differences were also found between the two blends of coffee in the burnt, caramel, nutty, earthy and roasty notes. Torrefacto coffee, widely consumed in Spain, is obtained by roasting coffee with sugar. Higher quantities of ketones, alcohols, pyrazines, furans, pyridines, alkanes, phenolic compounds, pyranones and terpenes were found in the blend A20:R80 50% Torrefacto coffee versus A20:R80 natural roasted coffee. These differences in the volatile fraction were perceived by our panellists in the intensities of the nutty, roasty, earthy, burnt and caramel notes.© 2002 Society of Chemical Industry

Characterization of the aroma of a meatlike process flavoring from soybean-based enzyme-hydrolyzed vegetable protein.

Defatted soybean meal was converted into enzyme-hydrolyzed vegetable protein (E-HVP) using the proteolytic enzyme Flavorzyme. Total free amino acids increased by 40-fold after enzyme hydrolysis, with leucine being the most abundant, followed by phenylalanine, lysine, glutamine/glutamic acid, and alanine. Volatile components from a meatlike process flavoring made from E-HVP were isolated by direct solvent extraction (DSE)-high vacuum transfer (HVT), dynamic headspace sampling and static headspace sampling and analyzed by gas chromatography (GC)-mass spectrometry and GC-olfactometry. Aroma extract dilution analysis was used to establish a flavor dilution chromatogram of the DSE-HVT extract. Results of these complementary techniques indicated the importance of odorants of high (hydrogen sulfide and methanethiol), intermediate (2-methyl-3-furanthiol, 3-mercapto-2-pentanone, 2-furanmethanethiol, and 3-(methylthiol)propanal) and low volatility (maltol and Furaneol) in the overall aroma of the meatlike process flavoring.

Static headspace gas chromatographic analysis of the residual solvents in gel extrusion module tablet formulations

A rapid static headspace-gas chromatographic (SHS-GC) method was developed and validated for the quantitation of residual solvents in pharmaceutical gel extrusion module (GEM) tablet formulations. A static headspace sampling technique was utilized to overcome the difficulties imposed by direct injection methods. A Rtx-1701 megabore capillary column was selected to achieve optimal resolution among organic volatile chemicals used commonly in the manufacturing of GEM tablets, residual solvents in the active ingredient and excipients, and other formulation matrix artifacts. A 50-mM pH 3.0 sodium phosphate buffer was used as a sample diluent to minimize matrix effects. The instrumental parameters of the SHS-GC method were optimized for sensitivity and precision. Quantitation was performed by external standard analysis. The SHS-GC method was validated according to regulatory requirements and produced acceptable results with respect to specificity, linearity, range, detection and quantitation limits, precision, and accuracy.

Fly-attracting volatiles produced by Rhodococcus fascians and Mycobacterium aurum isolated from myiatic lesions of sheep

Bacterial strains isolated from the healthy breech mucosa and myiatic wounds of ewes were tested for their volatile production as fly attractants towards Wohlfahrtia magnifica (Diptera: Sarcophagidae). Cultures were studied as fly baits in field experiments, and strains performing with the best chemotropic effect were selected for further analysis. Static and dynamic headspace samples from shaken cultures were examined by gas chromatography–mass spectrometry (GC–MS). Strains identified as Rhodococcus fascians and Mycobacterium aurum produced various volatile sulfur compounds and benzene, and proved to be the best fly attractants.

Biomonitoring of exposure to nitrous oxide, sevoflurane, isoflurane and halothane by automated GC/MS headspace urinalysis.

The goal of the present study was to develop an automated method to assess by biological monitoring, the volatile-anaesthetic exposure (nitrous oxide, sevoflurane, isoflurane and halothane) in operating theatre personnel. Post-shift urine samples were analysed by gas chromatography-mass spectrometry coupled with static headspace sampling (GC-MS/ HSS); intra-assay %-RSD (n= 10) was less than 5% for nitrous oxide and less than 7% for each halogenated vapour. The biomonitoring method was validated with air monitoring data, obtained by personal samplers and a similar GC-MS method. The sensitivity achieved by single ion monitoring (SIM) was sufficient to reveal low biological and environmental exposure averages down to 1 microg/l(urine) and 0.5 ppm for nitrous oxide and 0.1 microg/l(urine) and 50 ppb for halogenated compounds, respectively. In 1998 we collected and analysed 714 post-shift urine samples for the biological monitoring of volatile anaesthetics in the urine of the operating-theatre personnel of Sant'Orsola-Malpighi Hospital (Bologna, Italy). Our data showed that nitrous oxide (N20), the anaesthetic most largely used in general anaesthesia, is still the decisive factor in operating-theatre pollution. Moreover, on the basis of our results, working in close contact with anaesthetics seems to be the main determinant of risk: surgical nurses and anaesthesiologists are the most-exposed professional categories (mean post-shift urinary N2O approximately 65 microg/l(urine)) while general theatre staff, surgeons, and auxiliary personnel have significantly lower exposure. The biological monitoring of post-shift unmodified urinary volatile anaesthetics was confirmed to be a useful tool for evaluating individual exposure to these chemicals. The urinary concentrations of N2O and of halogenated vapours might reflect, to a certain extent, the external exposure to these compounds, and respiratory air-monitoring data support the validity of biological monitoring. Furthermore, the good relationship between air and urinary concentration of anaesthetics in people working in closer contact with these chemicals may be a good indirect means of revealing the bad air conditions of operating rooms, and may contribute to the highlighting and correction of service defects in anaesthesiology equipment and of human errors.

Optimizing headspace temperature and time sampling for identification of volatile compounds in ground roasted Arabica coffee.

Equilibration time and temperature were the factors studied to choose the best conditions for analyzing volatiles in roasted ground Arabica coffee by a static headspace sampling extraction method. Three temperatures of equilibration were studied: 60, 80, and 90 degrees C. A larger quantity of volatile compounds was extracted at 90 degrees C than at 80 or 60 degrees C, although the same qualitative profile was found for each. The extraction of the volatile compounds was studied at seven different equilibration times: 30, 45, 60, 80, 100, 120, and 150 min. The best time of equilibration for headspace analysis of roasted ground Arabica coffee should be selected depending on the chemical class or compound studied. One hundred and twenty-two volatile compounds were identified, including 26 furans, 20 ketones, 20 pyrazines, 9 alcohols, 9 aldehydes, 8 esters, 6 pyrroles, 6 thiophenes, 4 sulfur compounds, 3 benzenic compounds, 2 phenolic compounds, 2 pyridines, 2 thiazoles, 1 oxazole, 1 lactone, 1 alkane, 1 alkene, and 1 acid.

A water extraction, static headspace sampling, gas chromatographic method to determine MTBE in heating oil and diesel fuel.

A method was developed to determine the fuel/water partition coefficient (KMTBE) of methyl tert-butyl ether (MTBE) and then used to determine low parts per million concentrations of MTBE in samples of heating oil and diesel fuel. A special capillary column designed for the separation of MTBE and to prevent coelution and a gas chromatograph equipped with a photoionization detector (PID) were used. MTBE was partitioned from fuel samples into water during an equilibration step. The water samples were then analyzed for MTBE using static headspace sampling followed by GC/PID. A mathematical relationship was derived that allowed a KMTBE value to be calculated by utilizing the fuel/water volume ratios and the corresponding PID signal. KMTBE values were found to range linearly from 3.8 to 10.9 over a temperature range of 5-40 degrees C. This analysis method gave a MDL of 0.7 ppm MTBE in the fuel and a relative average accuracy of +/-15% by comparison with an independent laboratory using purge and trap GC/ MS analysis. MTBE was found in home heating oil in residential tanks and in diesel fuel at service stations throughout the state of Connecticut. The levels of MTBE were found to vary significantly with time. Heating oil and diesel fuel from terminals were also found to contain MTBE. This research suggests thatthe reported widespread contamination of groundwater with MTBE may also be due to heating oil and diesel fuel releases to the environment. used extensively for the past 20 years as a gasoline additive (up to 15 wt %) to reduce automobile carbon monoxide and hydrocarbon emissions. The fact that MTBE is highly soluble in water (approximately 5 wt %) (3) and chemically inert when compared to other fuel constituents causes it to be often detected at high concentrations in groundwater in the vicinity of gasoline spills. The EPA has reported that low levels of MTBE in drinking water (above 40 microg/L) may cause unpleasant taste and odors and has designated MTBE as a possible human carcinogen (4). Past studies have concentrated on the reporting of MTBE levels in groundwater near gasoline spills. Happel et al. reported an MTBE occurrence rate of approximately 78% at locations where hydrocarbons have impacted groundwater (5). Johnson et al. estimate that 9,000 leaking underground fuel tanks have caused MTBE contamination at community water supplies in the 31 states surveyed (excluding California and Texas) (6). Robbins et al. reported finding a significant number of MTBE detections in groundwater samples taken at sites in Connecticut known to be contaminated by heating oil spills (7). Later, this same research group reported finding MTBE contamination to range from 9.7 to 906 mg/L in heating oil and from 74 to 120 mg/L in diesel fuel in samples collected from storage tanks in Connecticut (8). The method used to analyze these samples was based on fuel-water partitioning and GC analysis. This present study provides the detailed basis for that analytical method. MTBE fuel-water partition coefficients as a function of temperature, which are critical to the method, are also presented. This study also reports on variations in MTBE levels as a function of time observed at several residences and a service station. Analytical results are reported for samples taken from terminals as part of an effort to assess the sources of MTBE in heating oil and diesel fuel.

Apparatus for the quantitative analysis of the aroma of french bread and its loss during storage.

Based on the principles of static and dynamic headspace sampling, an apparatus was developed for the determination of the release of potent odorants from two types of baguette (industrial process or "intensifée" and traditional or "artisanal") differing in their odor profiles. We applied this apparatus to get an insight into the aroma changes of freshly baked French bread, which develops a stale off-flavor within four hours after baking. Model mixtures containing the odorants in the concentrations found by the headspace analysis were evaluated using the apparatus as an olfactometer. By comparing the odor profiles of the models with those of the baguettes, the quantitative data were confirmed. The results indicate that losses of methylpropanal, 2- and 3-methylbutanal and, on the other hand, an increase of hexanal and (E)-2-nonenal led to a stale off-flavor. Furthermore it was suggested that this apparatus is also suitable for precise flavor release studies of other foods.

Flavour and off-flavour compounds of Swiss Gruyère cheese. Evaluation of potent odorants

Abstract The flavour of a typical sample of Gruyere cheese and that of a Gruyere exhibiting a potato-like off-flavour was examined by instrumental and sensory analyses. Based on the results of dynamic headspace gas chromatography-mass spectrometry (DHGC/MS), aroma extract dilution analysis (AEDA) and gas chromatography-olfactometry of static headspace samples (GCO-H), 2-/3-methylbutanal, methional, dimethyltrisulphide, phenylacetaldehyde, 2-ethyl-3,5-dimethylpyrazine, 2,3-diethyl-5-methylpyrazine, methanethiol, as well as butyric, 2-/3-methylbutyric and phenylacetic acid form the typical flavour of Gruyere cheese. The potato-like character of the sample showing an aroma defect, however, could not be attributed definitively to one of these compounds. Considering the results of DHGC/MS and AEDA, 2-ethyl-3,5-dimethylpyrazine and 2,3-diethyl-5-methylpyrazine could be the possible causes of the off-flavour.

Considerations on Static and Dynamic Sorptive and Adsorptive Sampling to Monitor Volatiles Emitted by Living Plants

Static and dynamic headspace sampling have been applied for the enrichment of volatiles emitted by living plants. For solid phase microextraction (SPME) the sorptive fibers polydimethylsiloxane (PDMS) and polyacrylate (PA) have been compared and, in accordance with the like-like principle, polar compounds exhibit more affinity for the PA fiber while apolar solutes favor the PDMS fiber. For dynamic sampling, tubes packed with PDMS particles show greater inertness than Tenax; some Tenax decomposition products, e.g. benzaldehyde and acetophenone, interfere with the analyses. With PDMS particles operated in the breakthrough mode, the obtained profiles are similar to those obtained by SPME on the PA fiber. Recoveries relative to a packed PDMS bed are 85% for Tenax, 2.4% for SPME-PDMS, and 6.2% for SPME-PA.

Array of conducting polymer sensors for the characterisation of wines

The response of an array of polymeric sensors to different Spanish wine varieties has been evaluated. Two different systems for the injection of the volatile compounds, based on static and dynamic headspace sampling, were used. A comparative study of the operation of the array when using one or the other methodology has been carried out. The cross sensitivity of the polymeric films to moisture and ethanol has been explicitly considered. The discrimination and classification capabilities of the sensor array have been examined by statistical analysis of the obtained data using pattern recognition techniques.

Potent odorants of boiled potatoes

The potent odorants of boiled potatoes were screened by aroma extract dilution analysis, aroma extract concentration analysis, and gas chromatography-olfactometry of static headspace samples. Altogether 45 odorants were found of which 42 were identified. trans-4,5-Epoxy-(E)-2-decenal, methional, 2-acetyl-1-pyrroline, dimethyltrisulfide, 2,3-diethyl-5-methylpyrazine, vanillin, sotolon, decanal, (E,E)-2,4-nonadienal, (E,E)-2,4-decadienal, (E)-β-damascenone, furaneol, methanethiol, 3-isopropyl-2-methoxypyrazine, dimethylsulfide appeared in at least one of the three screening experiments with a higher flavour dilution factor.

Sensory and Instrumental Assessments of the Ripening Process of Anchovy (Engraulis encrasicholus)

Sensory and instrumental assessments of anchovy ripening were carried out on samples from the same process at three different ripening stages, in an attempt to establish a relationship between sensory and analytical profiles. Screening of the potent volatiles by aroma extract dilution analysis (AEDA) in the three anchovy samples showed no significant differences between 4 and 8 months of ripening, while the sensory profiles differed in relation to the development of typical ripened aroma notes after 8 months. Results were consistent with a high contribution of highly volatile aldehydes to the desired matured aroma of the final product, as supported by a previous investigation. Ripening at 18°C is recommended for the best control of the process. Static headspace sampling methods can provide a means of objectively assessing the process using compounds, for example, acetaldehyde or 3-methyl butanal as indicator volatiles.

Rapid static headspace sampler for automated odour analysis

This paper describes the design and performance of an automated rapid static headspace sampler and a new axisymmetric temperature- controlled sensor chamber. The system is controlled via a virtual instrument embedded within a microcomputer and is capable of taking several hundred measurements per day. The headspace sampler has a repeatability of better than 1% with a dead-volume of only 3.1 ml and lag time of about 470 ms. The new sensor chamber operated at a constant temperature to better than ± 0.1° and gave a marked improvement in both sensor stability and response time, This new design of analytical instrument should provide for the superior analysis of odorant materials.

Identification and Quantification of Potent Odorants in Regular-Fat and Low-Fat Mild Cheddar Cheese

The potent odorants of regular-fat and low-fat Cheddar cheese were systematically characterized by aroma extract dilution analysis and gas chromatography/olfactometry of static headspace samples. Quantification of nine odorants using stable isotopes as the internal standards and calculation of odor activity values revealed methional, 2(5)-ethyl-5(2)-methyl-4-hydroxy-3(2H)-furanone (homofuraneol), diacetyl, acetic acid, and butyric acid as odorants with high aroma impact. Among the highly volatile compounds, the role of methanethiol and dimethyl sulfide for the nasal perception of the cheese flavor was established. The low-fat Cheddar cheese had a meaty-brothy odor defect that is believed to be caused by significantly higher amounts of 4-hydroxy-2,5-dimethyl-3(2H)-furanone (Furaneol), homofuraneol, and methional in this cheese. Keywords: Cheddar cheese; regular fat; low fat; AEDA; static headspace; odor activity value

Identification of Character Impact Odorants of Different White Wine Varieties

Application of gas chromatography/olfactometry (GC/O) to the analysis of extracts of Scheurebe and Gewürztraminer wines yielded 36 and 40 odor-active compounds, respectively. Ethyl 2-methylbutyrate, ethyl isobutyrate, 2-phenylethanol, 3-methylbutanol, 3-hydroxy-4,5-dimethyl-2(5H)-furanone, 3-ethylphenol, and an unknown compound named wine lactone showed high flavor dilution factors in both varieties. Wine lactone was identified as 3a,4,5,7a-tetrahydro-3,6-dimethylbenzofuran-2(3H)-one and was detected for the first time among the volatiles of wine or a food. The compound exhibited an intense coconut, woody, and sweet odor. 4-Mercapto-4-methylpentan-2-one belongs to the most potent odorants only in the variety Scheurebe, whereas cis-rose oxide was a key substance for the overall flavor of Gewürztraminer wine. GC/O of static headspace samples of both wine varieties revealed butane-2,3-dione, dimethyl sulfide, and dimethyl trisulfide as further potent odorants. Keywords: Gas chromatography/olfactometry; 3a,4,5,7a-tetrahydro-3,6-dimethylbenzofuran-2(3H)-one; cis-rose oxide; 4-mercapto-4-methylpentan-2-one; white wine; flavor; aroma; Gewürztraminer; Scheurebe

Decomposition of transformer oils: a new approach for the determination of dissolved gases

The possibility of using a static headspace sampling technique for introducing gases into a chromatograph and performing dissolved-gas analysis automatically was demonstrated in a previous work. The main drawback of the method was the relatively long time that the analytes take to equilibrate between the oil and the headspace. In this paper, the application of mechanical agitation to a viscous matrix to enhance diffusion of the species during the equilibration period was investigated together with the use of an improved nickel catalyst system and a new porous-layer open tubular chromatographic column. The analytical performance of the technique is established and compared with that of method A of the ASTM D 3612 standard procedure. The comparison shows that the technique can be used to assess dissolved gases with the same precision in a much shorter time with a higher sensitivity of detection. An excellent correlation was observed between the analytical results of the two techniques applied to 35 transformer oil samples. The high sensitivity of detection achieved means that transformer fault diagnosis can now be extended to equipment newly commissioned or apparatus other than open breathing equipment, where the total gas content in oil is very low.

Blood Alcohol Determination with Automated Solid Phase Microextraction (SPME): A Comparison with Static Headspace Sampling

ABSTRACTEthanol in the blood or urine of suspected intoxicated drivers is commonly measured using static headspace GC. In this study, a new sampling technique, solid phase microextraction (SPME), was compared with conventional static headspace. Aqueous ethanol standards were sampled using a SPME fibre installed in a GC autosampler, modified for automated SPME. Linearity was demonstrated over the range 0–500 mg/100 mL with excellent precision. Next, blood and urine samples from California drivers were split and analyzed with static headspace and with SPME. The ethanol levels determined with the two techniques were similar: the correlation coefficient (r2) between the two sets of values was 0.9946.Advantages of SPME over conventional static headspace included relatively compact and less expensive hardware and no trace of sample carryover.

Aqueous alkylation of anions for static headspace sampling with analysis by capillary gas chromatography‐mass spectrometry

AbstractThe formation of ethyl derivative from anions and the conjugate bases of weak acids through the reaction with ethyl p‐toluenesulfonate in strongly basic aqueous systems was used as a precursor to analysis by static headspace sampling with capillary gas chromatography‐mass spectrometry. A host of materials are amenable to the technique including: cyanide, butyrate, caproate, fluoroacetate, iodide, and phenol. These analytes were used to study the performance of the system in relation to the behavior of commercially obtained ethyl derivatives. 18‐Crown‐6 (1,4,7,10,13,16‐hexaoxacyclooctadecane) effectively catalyzes the reaction which appears to require the presence of high concentrations (5 M) of a basic salt, such as potassium carbonate. A 1:1 (molar) mixture of dibasic and tribasic potassium phosphate effectively substitutes for potassium carbonate and provides improved performance for fluoroacetate while reducing interferences such as diethyl carbonate. Quantitative yields were obtained in the concentration range 0.05‐2 mM, except for cyanide which produced propionitrile with an efficiency of 55–80%. Fructose, at the 10% w/v level, exerted little influence upon the reaction. Calibration curves (selected ion monitoring) were linear between 0.001 and 1 mM. This approach extends the applicability of static headspace sampling and offers a potentially simple alternative to ion chromatography for complicated matrices. It should prove useful for confirming results obtained by other methods or for screening poorly characterized samples. © 1995 John Wiley & Sons, Inc.

Determination of Partition Coefficients and Quantitation of Headspace Volatile Compounds

A survey of partition coefficient values reported in the literature showed numerous discrepancies. These could be attributed to technical problems encountered during headspace measurements. Consequently, a novel method based on a combination of static headspace sampling and dynamic headspace traps was developed. The new method also includes determination of partition coefficients independently of the concentration of the reference. Once the partition coefficient is known, a simple calibration of the gas phase constituents can be performed. This headspace quantification method does not require addition of a standard. Estimation of variance showed the method to be accurate (0.5-15%, depending on component and matrix). A model mixture of flavors was investigated by the new method. Varying the concentration of one compound had no effect on the rest of the aroma profile. Small differences in the aroma profile due to changes in the matrix were investigated as exemplified by alterations in flavor retention observed when water, lipids, or emulsions were used as the solvent.