Sampling Of Volatiles Research Articles

Investigation of solid-phase microextraction efficiency using pencil lead fiber for in vitro and in vivo sampling of defensive volatiles from insect's scent gland

A new in vitro and in vivo solid-phase microextraction (SPME) sampling method using pencil lead fiber coupled with gas chromatography was developed for a fast, easy and reliable monitoring and recognition of volatile defensive chemical of scent gland of Graphosoma Lineatum (L.) ( Heteroptera Pentatomidae). The efficiency of three methods: (1) in vitro surgical sampling and direct injection in GC analysis known as a classical method, (2) in vitro surgical sampling, SPME/GC analysis and (3) in vivo SPME/GC method were investigated. The efficiency and reliability of homemade pencil lead fiber was evaluated and compared by commercial polydimethylsiloxane (PDMS) fiber. Some effective and experimental parameters, such as extraction time, chromatographic conditions were examined and optimized. The obtained results reveal that the in vivo SPME/GC is much better than in vitro pentane extraction of volatile compounds followed by either headspace SPME or direct injection and GC analysis. From the results obtained, for the studied chemicals, the extraction capacity of pencil lead fiber is about 1000-fold more than commercial PDMS fiber.

Plume chemistry provides insights into mechanisms of sulfur and halogen degassing in basaltic volcanoes

This paper deals with sulfur, chlorine and fluorine abundances in the eruptive volcanic plume of the huge October 2002–January 2003 eruption of Mount Etna, aiming at relating the relevant compositional variations observed throughout with changes in eruption dynamics and degassing mechanisms. The recurrent sampling of plume acidic volatiles by filter-pack methodology revealed that, during the study period, S/Cl and Cl/F ratios ranged from 0.1–6.8 and 0.9–5.6, respectively. Plume S/Cl ratios increased by a factor of ∼10 as volcanic activity drifted from paroxysmal lava fountaining (mid- and late November) to passive degassing and minor effusion (early January), and then decreased to the low values (S/Cl=0.1) typical of the final stages of the eruption. Parallel variations in chlorine to fluorine ratios were also observed. A theoretical model is proposed for quantitative interpretation of these changes in plume composition. The model calculates the composition of a volatile phase exsolving from an ascending Etna magma, based on knowledge of solubilities and abundances in the undegassed melt of sulfur and halogens [T.M. Gerlach, EOS 72 (1991), 249, 254–255]. According to this model, degassing of Etnean basaltic melt at high pressures and depths (>100 MPa, 3 km) is likely to release a CO2+H2O-rich vapor phase with S/Cl molar ratios ∼1. Extensive sulfur and chlorine degassing from the melt would take place at shallower depth (P<20 MPa, 0.6 km), with S/Cl ratios in the vapor phase increasing as pressure drops to 0.1 MPa. Comparisons between model compositions and volcanic plume data demonstrate that the chemical trends observed during the eruption may be explained by increased degassing due to depressurization of a basaltic magma batch ascending toward the surface.

Plume chemistry provides insights into mechanisms of sulfur and halogen degassing in basaltic volcanoes

This paper deals with sulfur, chlorine and fluorine abundances in the eruptive volcanic plume of the huge October 2002–January 2003 eruption of Mount Etna, aiming at relating the relevant compositional variations observed throughout with changes in eruption dynamics and degassing mechanisms. The recurrent sampling of plume acidic volatiles by filter-pack methodology revealed that, during the study period, S/Cl and Cl/F ratios ranged from 0.1–6.8 and 0.9–5.6, respectively. Plume S/Cl ratios increased by a factor of ∼10 as volcanic activity drifted from paroxysmal lava fountaining (mid- and late November) to passive degassing and minor effusion (early January), and then decreased to the low values (S/Cl=0.1) typical of the final stages of the eruption. Parallel variations in chlorine to fluorine ratios were also observed. A theoretical model is proposed for quantitative interpretation of these changes in plume composition. The model calculates the composition of a volatile phase exsolving from an ascending Etna magma, based on knowledge of solubilities and abundances in the undegassed melt of sulfur and halogens [T.M. Gerlach, EOS 72 (1991), 249, 254–255]. According to this model, degassing of Etnean basaltic melt at high pressures and depths (>100 MPa, 3 km) is likely to release a CO2+H2O-rich vapor phase with S/Cl molar ratios ∼1. Extensive sulfur and chlorine degassing from the melt would take place at shallower depth (P<20 MPa, 0.6 km), with S/Cl ratios in the vapor phase increasing as pressure drops to 0.1 MPa. Comparisons between model compositions and volcanic plume data demonstrate that the chemical trends observed during the eruption may be explained by increased degassing due to depressurization of a basaltic magma batch ascending toward the surface.

Ultrafast sampling and analysis of plant volatiles by a hand-held miniaturised GC with pre-concentration unit: Kinetic and quantitative aspects of plant volatile production

A method has been developed for continuous monitoring of the emission of volatiles from biological sources with high time resolution. High time resolution (up to 3 min) is achieved by an automatically operated, miniaturised gas chromatographic system equipped with a pre-concentration unit (zNoseTM). After calibration, the zNoseTM provides reliable quantitative data for individual compounds and allows their emission kinetics to be followed over longer periods of time without supervision. While the results of the zNoseTM provide information about actual composition of aromas during sampling, the analysis of simultaneously trapped volatiles supplies information about the total amount of emitted compounds and permits further spectroscopic analyses (Isotope-Ratio-MS, GC-MS, etc.). Both methods, analysis by the zNoseTM and sampling on charcoal traps, lead to comparable results. The new analytical system has been successfully used to study the kinetics of volatile emission from elicitor-treated Lima bean leaves (Phaseolus lunatus), aphid-damaged paprika plants (Capsicum annuum), and to follow the volatile emission from blossoms of the cactus Rebutia fabrisii over several days. The instrument is portable and can be used in the field.

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

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.

Quantitative Determination of Vapor-Phase Compound A in Sevoflurane Anesthesia Using Gas Chromatography–Mass Spectrometry

During low-flow or closed-circuit anesthesia with the fluorinated inhalation anesthetic sevoflurane, compound A, an olefinic degradation product with known nephrotoxicity in rats, is generated on contact with alkaline CO(2) adsorbents. To evaluate compound A formation and thus potential sevoflurane toxicity, a reliable and reproducible assay for quantitative vapor-phase compound A determination was developed. Compound A concentrations were measured by fully automated capillary gas chromatography-mass spectrometry with cryofocusing. Calibrators of compound A in the vapor phase were prepared from liquid volumetric dilutions of stock solutions of compound A and sevoflurane in ethyl acetate. 1,1,1-Trifluoro-2-iodoethane was chosen as an internal standard. The resulting quantitative method was fully validated. A linear response over a clinically useful concentration interval (0.3-75 microL/L) was obtained. Specificity, sensitivity, and accuracy conformed with current analytical requirements. The CVs were 4.1-10%, the limit of detection was 0.1 microL/L, and the limit of quantification was 0.3 microL/L. Analytical recoveries were 100.6% +/- 10.1%, 102.5% +/- 7.3%, and 99.0% +/- 4.1% at 0.5, 10, and 75 microL/L, respectively. The method described was used to determine compound A concentrations during simulated closed-circuit conditions. Some of the resulting data are included, illustrating the practical applicability of the proposed analytical approach. A simple, fully automated, and reliable quantitative analytical method for determination of compound A in air was developed. A solution was established for sampling, calibration, and chromatographic separation of volatiles in an area complicated by limited availability of sample volume and low concentrations of the analyte.

Equilibrium Sorptive Enrichment on Poly(dimethylsiloxane) Particles for Trace Analysis of Volatile Compounds in Gaseous Samples

A novel approach for sample enrichment, namely, equilibrium sorptive enrichment (ESE), is presented. A packed bed of sorption (or partitioning) material is used to enrich volatiles from gaseous samples. Normally, air sampling is stopped before breakthrough occurs, but this approach is not very successful for weakly retained compounds (volatiles) as early breakthrough occurs. In ESE, sampling is continued until all compounds of interest are in equilibrium with the sorptive material. This allows accurate sampling of volatiles and enrichment at the maximum attainable sensitivity. However, due to the equilibrium nature of ESE, it is limited to samples with a constant concentration over the sampling time. This requirement is easily met for those compounds with short equilibration times (volatiles). Because of the nature of the sorption mechanism, which is basically dissolution, all compounds partition independently into the sorbent (stationary phase) and displacement effects do not occur. This is a great advantage over adsorption materials. Additionally, theory allows the calculation of enrichment factors from literature retention indexes. Moreover, ESE also benefits from the features of sorption materials such as a very high inertness and interference-free blanks. The performance of ESE is illustrated with the analysis of several analytes including the epoxides ethylene oxide and epichlorohydrin in real-life air sampling.

Isolation and quantification of volatiles in fish by dynamic headspace sampling and mass spectrometry.

A dynamic headspace sampling method for isolation of volatiles in fish has been developed. The sample preparation involved freezing of fish tissue in liquid nitrogen, pulverizing the tissue, and sampling of volatiles from an aqueous slurry of the fish powder. Similar volatile patterns were determined by use of this sample preparation method and for samples chewed for 10 s. Effects of sampling time, temperature, and purge flow on level of volatiles were tested. Purging at 340 mL/min for 30 min at 45 degrees C was found to be optimal. Detection limits for a number of aldehydes were 0.2-2.7 microg/kg. Levels of volatiles are given for fresh salmon, cod, saithe, mackerel, and redfish.

Books: Sampling and analysis of volatiles

Books: Sampling and analysis of volatiles

The development of an improved method for the determination of coal tar pitch volatiles (CTPV) in air

Test samples were collected at a range of sites using the MDHS 68 sampler, a 7-hole sampler, and a cyclone respirable-dust sampler. Glass fibre, Zefluor, Fluoropore and silver (0.8 and 5μm) filters were compared for weighing error, handling characteristics, and amount collected. The effects of a carbon back-up, of extraction solvent, and of analytical method were studied. The current HSE method for the sampling and analysis of coal tar pitch volatiles, MDHS 68 has been reviewed. It is recommended that the MDHS 68 sampler be replaced by a 7-hole head containing a silver or PTFE filter ($̃1 μm pore size), with a graphitised carbon back-up if efficient collection of 2 to 4-ring PAHs is required. Cyclohexane is recommended as the extraction solvent. Methods of analysis which quantify the fume as a whole (MDHS 68, u.v., ELSD) were shown to give a response which varied according to the type of CTPV generating process. Therefore analysis of specific PAHs of occupational interest, by GC-MS or HPLC is recommended.

The Development of an Improved Method for the Determination of Coal Tar Pitch Volatiles(CTPV) in Air

Test samples were collected at a range of sites using the MDHS 68 sampler, a 7-hole sampler, and a cyclone respirable-dust sampler. Glass fibre, Zefluor, Fluoropore and silver (0.8 and 5pm) filters were compared for weighing error, handling characteristics, and amount collected. The effects of a carbon back-up, of extraction solvent, and of analytical method were studied. The current 1-ISE method for the sampling and analysis of coal tar pitch volatiles, MDHS 68 has been reviewed. It is recommended that the MDHS 68 sampler be replaced by a 7-hole head containing a silver or PTFE filter (∼1 μ pore size), with a graphitised carbon back-up if efficient collection of 2 to 4-ring PAHs is required. Cyclohexane is recommended as the extraction solvent. Methods of analysis which quantify the fume as a whole (MDHS 68, u. ELSD) were shown to give a response which varied according to the type of CTPV generating process. Therefore analysis of specific PAHs of occupational interest, by CC-MS or HPLC is recommended. Crown copyright © 1998 Published by Elsevier Science Ltd.

Rapid Analysis of Volatile Flavor Compounds in Apple Fruit Using SPME and GC/Time-of-Flight Mass Spectrometry

Solid-phase microextraction (SPME), time-compressed chromatography (TCC), and time-of-flight mass spectrometry (TOFMS) were examined for their suitability and compatibility for rapid sampling, separation, and detection of apple flavor volatiles. Flavor-contributing volatile compounds were found to have relatively high partition coefficients on a 100 μm thick coating of polydimethylsiloxane (PDMS) on a SPME fiber. The time required to saturate the PDMS coating was highly volatile-dependent, varying from less than 2 min to greater than 30 min. However, the response of this system was linear in the ppb to ppm range when the adsorption duration was standardized. The speed of the TOF mass spectrometer permitted identification and quantification of compounds having chromatographic peak widths of only a fraction of a second. The unskewed nature of fragmentation patterns obtained allowed individual component spectral characterization of unknown compounds even when not fully chromatographically separated. Thus, the time required for chromatography could be reduced by an order of magnitude without loss in analytical performance. Typical analysis times for complex mixtures were 2−5 min as compared with 20−60 min required for standard purge-and-trap analyses. Keywords: SPME (solid-phase microextraction); time-compressed chromatography; time-of-flight mass spectrometry; headspace sampling; partition coefficient; purge-and-trap; volatiles; flavor; apples

A method for collection, long-term storage, and bioassay of labile volatile chemosignals

A procedure for headspace sampling and long-term storage of organic volatiles coupled with gas chromatographic-mass spectrometric (GC-MS) analysis was used to study the volatile chemosignals in a biological secretion prior to bioassay. The approach involved collecting the volatiles in evacuated canisters from an apparatus in which 1 ml of secretion was dispersed for headspace sampling. These canisters, stainless steel, 850 ml, and 100% internally electropolished, have been demonstrated to store volatile compounds, in chemically stable form, for several weeks. The GC-MS analyses provided the quantitation and identification of compounds from C3 through C14 at concentrations as low as 0.10 parts per billion volume. The approach was used to study chemosignals of musth temporal gland secretions (TGS) from a male Asian elephant (Elephas maximus). Fresh TGS material loses its biological activity within 1 hr. TGS material stored at -20°C usually looses its activity within 30 days. The usefulness of this method for long-term storage of the volatile chemosignals was demonstrated by the retention of biologically active TGS headspace compounds, as determined through bioassays, stored in these canisters for one year.

Evaluation of adsorbents for sampling and quantitative analysis of microbial volatiles using thermal desorption-gas chromatography

Eight adsorbents were evaluated for sampling and quantitative analysis of microbially produced volatiles using thermal desorption-gas chromatography. The adsorbents studied were Tenax TA, Tenax GR, Chromosorb 102, Carbotrap C, Carbopack B, Anasorb 727, Anasorb 747 and Porasil C/n-octane (Durapak). The study was performed using a test atmosphere consisting of ten compounds differing in polarity and volatility: 2-propanol, dimethyl disulfide, toluene, furfural, 1-octen-3-ol, 3-octanone, 3-octanol, 2-isopropyl-3-methoxypyrazine, 2-methylisoborneol and geosmin. The adsorbents were tested under conditions found in “sick buildings”—low μg/m3 levels and varying humidity. Tenax TA proved to have the best properties considering the amount obtained, breakthrough and standard deviation during sampling/analysis.

Air Sampling of Volatiles from Agaricus bisporus in a Mushroom Facility and from Mushroom Compost

Air sampling using Tenax, a selective solid absorbent, was performed from spawning to pinning over the duration of four mushroom crops of Agaricus bisporus (Lange) Imbach (Fungi; Agricaceae). The contents of the air sampling tubes were thermally desorbed directly to a gas chromatograph-mass selective detector. In two crops 3-octanone and 1-octen3-ol were detected 12 to 13 days after spawning. These two compounds were also detected after compost was added at casing (CAC) and the ketone was present in large quantities. Air sampling of a 10-g sample of spawned compost vs. unspawned compost confirmed that these two compounds were of fungal origin. Bags of spawned compost were used to determine the effects of a CAC layer, a soybean supplement, and Spawn Mate on the volatiles released by the spawned compost. The CAC layer and the soybean supplement selectively absorbed 1-octen-3-ol and, to a lesser extent, 3-octanone. The addition of Spawn Mate to the compost at spawning did not alter the quantity or ratio of 3-octanone to 1-octen-3-ol released by the spawned compost.

Sampling of organic volatiles in the atmosphere at moderate and low pollution levels

Several techniques are available for measuring organic volatiles in the atmosphere. For measurements at low and moderate pollution levels (between several μg m −3 and a fraction of a μg m −3), the existing methods can be adopted to a broad range of different compounds. Whole-air sampling in stainless-steel containers with metal bellows valves combined with subsequent gas chromatographic separation after preconcentration in the laboratory is probably the best procedure for low and medium molecular weight trace gases of moderate or low polarity and reasonable chemical stability (e.g., hydrocarbons and halocarbons). For organic compounds of lower volatility, adsorptive sampling on non-polar porous organic polymers (e.g., Tenax) and thermal desorption combined with cryotrapping and gas chromatographic separation of the sampled compounds is widely used. However, there are often substantial problems due to artefact formation or loss reactions. Owing to the generally larger sample volumes, these problems are even more pronounced for sorptive sampling techniques combined with sample recovery by solvent extraction. Unfortunately, the general understanding of the various processes of sample degradation due to chemical reactions of reactive components of the atmosphere with each other or with the sorbent is not yet sufficient to allow reasonable estimates of the extent of such interferences without elaborate test procedures.

High-precision sampling of trace gas-borne volatiles by the dynamic solvent effect with a comparative review of alternative techniques

The precise determination of traces of organic volatiles is particularly challenging in semiochemistry and clinical chemistry, where specimen sizes are intrinsically limited and amounts of trace components correspondingly very small. This demands a sampling technique that is fully compatible with the ability of capillary columns and gas chromatographic detectors to separate and quantify nanogram and sub-nanogram amounts from complex mixtures. The quantitative precision of dynamic solvent-effect sampling of low parts per billion (10 9) aqueous carbonyl compounds, high ppb and low parts per million aqueous phenols, low ppb and high parts per trillion (10 12) airborne hydrocarbons and the volatiles from wine, human urine and a slow-release pesticide was tested with specimen sizes that yielded amounts of volatiles down to the sub-nanogram level. Provided that sources of variability, such as temperature changes, adsorption on containers, incomplete peak resolution and changes in the specimens themselves, were adequately controlled, dynamic solvent-effect sampling consistently provided coefficients of variation in peak areas, peak percentage areas and peak-area ratios of less than 10% at nanogram and sub-nanogram levels. The literature was surveyed for data on the performance of other sampling systems. None of them have been demonstrated to match the precision of the dynamic solvent effect with such small amounts from such a wide range of materials.

Rhythms of fragrance emission in flowers

A method for the sampling of volatiles emitted by individual flowers is described. Sampling over periods of 3 h allowed the examination of diurnal changes in quantity and quality of fragrance. In the species studied, Odontoglossum constrictum Lindl., Citrus medica L., Hoya carnosa R. Br., and Stephanotis floribunda Brongs., the fragrance was characterized by a few major components accompanied by a larger number of minor components. Flowers of all species produced volatiles in a rhythmical, diurnal fashion. Whereas in detached flowers of O. constrictum and C. medica rhythmicity could be observed for up to four cycles, flowers of H. carnosa showed this phenomenon only when attached to the plant. Maxima of emission were observed during the day in C. medica and O. constrictum whereas in H. carnosa it occurred during the night. In S. floribunda a conspicuous asynchronism of the emission of different volatiles was observed, resulting in the rhythmical change of fragrance quality.

A comparison between different high volume sampling systems for collecting ambient airborne particles for mutagenicity testing and for analysis of organic compounds

Samples of urban air were collected simultaneously using different sampling systems, including electrostatic precipitation (ESP) and high volume filtration (HVF) on various filters for particle sampling and adsorption on activated carbon and organic polymers for sampling of volatiles. Acetone extracts of the samples were analyzed for polycyclic aromatic hydrocarbons (PAH) and tested for mutagenicity with the Ames Salmonella/microsome assay. The results show that the concentrations of PAH found in the various particle-samples were in good agreement, whereas the mutagenic activity of these samples showed large variations. The highest mutagenic activity was found in the samples collected by ESP and on the teflon-coated glassfibre filters, whereas samples collected by high volume filtration with size-fractionation showed the lowest mutagenic activity. We do not know whether the higher activity in samples from the teflon-coated filters compared to those from ordinary glassfibre filters represent filter artifacts or if it represents a more pronounced degradation of mutagenic compounds on the non-coated glassfibre filters. Extracts from filter blanks seemed to interfere with the expression of the mutagenic activity of the positive controls, benzo[ a] pyrene and nitropyrene. When sampling volatile compounds, two organic polymers, polyurethane (PUR) and XAD-2, were found suitable for collecting PAH, whereas no PAH could be detected in extracts from the activated carbon. The XAD-2 adsorbent was the most effective for sampling bicyclic PAH. None of the adsorbents yielded extracts well studied for mutagenicity testing, since blank extracts were toxic to the test bacteria. Some extracts of the PUR blanks were weakly mutagenic as well. More emphasis should be placed upon developing more efficient and unreactive adsorbents and on the adaptation of such adsorbents in samplers suited for routine use.

Headspace Sampling Procedures for Onion (Allium cepa L.) Aroma Assessment

In order to study the effect of nutrition, irrigation, variety and dehydration on onion flavor strength, analytical procedures based on headspace sampling of volatiles were evaluated. A procedure using a porous polymer, Tenax–GC; to concentrate the headspace volatiles by trapping followed by gas chromatography with or without a liquid phase column was found to be most suitable. Reproducibility of the results required standardization of the sampling procedure. Of major importance were the extent of sample disintegration, incubation temperature, timing and the rehydration ratio of dehydrated samples. Quantitative data for the volatiles of fresh onion slices were also provided and compared with those dehydrated by a pilot–scale process.