Novel sample preparation technique with needle-type micro-extraction device for volatile organic compounds in indoor air samples

A novel needle-type sample preparation device was developed for the effective preconcentration of volatile organic compounds (VOCs) in indoor air before gas chromatography–mass spectrometry (GC–MS) analysis. To develop a device for extracting a wide range of VOCs typically found in indoor air, several types of particulate sorbents were tested as the extraction medium in the needle-type extraction device. To determine the content of these VOCs, air samples were collected for 30 min with the packed sorbent(s) in the extraction needle, and the extracted VOCs were thermally desorbed in a GC injection port by the direct insertion of the needle. A double-bed sorbent consisting of a needle packed with divinylbenzene and activated carbon particles exhibited excellent extraction and desorption performance and adequate extraction capacity for all the investigated VOCs. The results also clearly demonstrated that the proposed sample preparation method is a more rapid, simpler extraction/desorption technique than traditional sample preparation methods.     

An eco-friendly efficient extractor

A microscale solid-liquid Pyrex extractor is described. The extractor has a novel detachable extraction vessel (H) containing a filter paper cylinder (C) over the reservoir. A filter paper cylinder (C) is firmly placed in the socket (E) with a plug (G) on which the cylinder has been placed. The sample is directly weighed in the extraction vessel (H) and the vessel is clamped (F) to the body (B). Contents in the extraction reservoir (H) are stirred (I) with a magnetic stirrer (J) and heated sufficiently (e.g. at 84.8 °C in using water) by the solvent vapor (D). Easy filtration (C) and continuous outflow (D) of the filtrates out of the reservoir (H) keeps a stable boiling condition (K), rather than batchwise conditions operative in a Soxhlet; this results in rapid and exhaustive extraction. The present extractor (8.0 mL extraction reservoir (H) capacity) equipped with a 25 mL solvent flask (K) was applied to fat extraction from powdered peanut by using 18 mL of ether. The extraction was complete in 30-60 min depending on reflux rate; in contrast, extraction with a commercial micro-Soxhlet device (23.9 mL extraction reservoir capacity) equipped with a 25 mL flask by using 34 mL of the solvent was incomplete in 120 min. Unlike filter paper thimbles used in Soxhlet devices, filter paper cylinder (C) in the new extractor could be reused many times and results in significant savings of the filter paper cylinders. Small reservoir and flask capacities of the new extractor minimize the use of organic solvents. The present apparatus permits fast and efficient extraction, sharply reduces waste, minimizes solvent consumption, and thus should find wide use aiming at the Green Solutions to Global Problems.     

Solid-phase microcolumn extraction and gas chromatography-mass spectrometry identification of volatile organic compounds emitted by paper

A rapid non-destructive sampling technique for the analysis of volatile organic compounds (VOCs) emitted by paper sheets is described. A capillary, which is connected to a microcolumn packed with Tenax TA, is inserted between two sheets at the centre of a paper stack encapsulated inside a PET/Al/PE composite foil. The other end of the microcolumn is connected to a gas-tight syringe and an appropriate volume of gaseous phase is aspirated. The microcolumn is then thermally desorbed in a modified GC inlet (modification is presented) and analysed by gas chromatography-mass spectrometry (GC-MS). In the chromatogram from the analysis of artificially aged paper sample 21 compounds were identified. Advantages of the method including the short sampling time (1 min), simplicity and economic aspect are discussed.     

Comparative analysis of odorous volatile organic compounds between direct injection and solid-phase microextraction: Development and validation of a gas chromatography–mass spectrometry-based methodology

In this study, the feasibility of GC–MS was evaluated for the quantification of odorous volatile organic compounds (VOCs) in environmental samples. These included methyl ethyl ketone, isobutyl alcohol, methyl isobutyl ketone, and butyl acetate plus benzene, toluene, and xylene (BTX). For this purpose, the gaseous standard for these VOCs were analyzed by GC–MS with the aid of both direct injection (DI) into the GC injector and solid-phase microextraction (SPME). The liquid phase standard prepared independently was tested additionally by the DI method as a reference to gaseous calibration. The detection limit (DL) values, when tested for basic quality assurance in this study, showed large differences between DI (0.002–0.007 ng) and SPME method (1.03–1.81 ng) in terms of absolute mass. The DL values, when expressed in terms of concentration (v/v), showed considerable improvement in SPME (below 0.40 nmol mol⁻¹) relative to the DI method (∼6–15 nmol mol⁻¹). The reliability of the GC–MS method was further validated through an analysis of real environmental samples collected from an industrial area.     

Optimization of SPME-Arrow-GC/MS Method for Determination of Free and Bound Volatile Organic Compounds from Grape Skins

(1) Background: Solid phase microextraction (SPME)-Arrow is a new extraction technology recently employed in the analysis of volatiles in food materials. Grape volatile organic compounds (VOC) have a crucial role in the winemaking industry due to their sensory characteristics of wine.; (2) Methods: Box–Behnken experimental design and response surface methodology were used to optimise SPME-Arrow conditions (extraction temperature, incubation time, exposure time, desorption time). Analyzed VOCs were free VOCs directly from grape skins and bound VOCs released from grape skins by acid hydrolysis.; (3) Results: The most significant factors were extraction temperature and exposure time for both free and bound VOCs. For both factors, an increase in their values positively affected the extraction efficiency for almost all classes of VOCs. For free VOCs, the optimum extraction conditions are: extraction temperature 60 °C, incubation time 20 min, exposure time 49 min, and desorption time 7 min, while for the bound VOCs are: extraction temperature 60 °C, incubation time 20 min, exposure time 60 min, desorption time 7 min.; (4) Conclusions: Application of the optimized method provides a powerful tool in the analysis of major classes of volatile organic compounds from grape skins, which can be applied to a large number of samples.     

Determination of volatile organic compounds in contaminated air using semipermeable membrane devices

Semipermeable membrane devices (SPMDs) were evaluated as passive samplers for the determination of 26 volatile organic compounds (VOCs) in contaminated air of occupational environments. A direct methodology based on the use of head-space-gas chromatography-mass spectrometry (HS-GC-MS) was developed for VOCs determinations in SPMDs, without any sample pre-treatment and avoiding the use of solvents. A desorption temperature of 150 °C for 10 min was sufficient for a sensitive VOCs determination providing limits of detection in the range of 15 ng SPMD⁻¹ for 21 of 26 studied compounds. Linear and equilibrium uptake models were established for each VOC from compound isotherms. Highly volatile compounds were slightly absorbed and moderately volatile compounds were strongly absorbed by SPMDs. This study is the first precedent of the use of SPMDs for the simultaneous sampling of a wide number of VOCs. The use of SPMDs is a simple and low cost alternative to ordinary sampling devices such as Radiello^® diffusive samplers or badge-type solid-phase supports.     

Development of solid-phase microextraction followed by gas chromatography-mass spectrometry for rapid analysis of volatile organic chemicals in mainstream cigarette smoke

In this work, a novel, simple and efficient method based on solid-phase microextraction (SPME) followed by gas chromatography-mass spectrometry (GC-MS) was developed to the analysis of volatile organic chemicals (VOCs) in mainstream cigarette smoke (MCS). Using a simple home-made smoking machine device, extraction and concentration of VOCs in MCS were performed by SPME fiber, and the VOCs adsorbed on fiber were desorbed, and analyzed by GC-MS. The extraction fiber types and the desorption conditions were studied, and the method precision was also investigated. After the investigation, the optimal fiber was divinylbenzene/carboxen/polydemethylsiloxane (DVB/CAR/PDMS), and the optimal desorption condition was 250 degrees C for 3 min. The method precision was from 2% to 11%. Finally, the proposed method was tested by its application of the analysis of VOCs in MCS from 10 brands of cigarettes and one reference cigarette. A total of 70 volatile compounds were identified by the proposed method. The experimental results showed that the proposed method was a simple, rapid, reliable, and solvent-free technique for the determination of VOCs in MCS.     

Enhancement reagents for simultaneous vapor generation of zinc and cadmium with intermittent flow system coupled to atomic fluorescence spectrometry

Simultaneous vapor generation of zinc (Zn) and cadmium (Cd) was evaluated by atomic fluorescence spectrometry coupled with an intermittent flow vapor generation system. Some complexing reagents, surfactant and transition metal ions were respectively tested as enhancement reagents. Experiments showed that an appropriate amount of 8-hydroxyquinoline or phenanthroline and nickel ion simultaneously, effectively improved the vapor generation efficiency of Zn and Cd. The volatile species generation was presumed to be a hydrogenation process interpreting how the enhancement reagents played an important role in vapor generation. Additionally, due to the instability of volatile species, reaction temperature, rapid and sufficient mixing of reagents and rapid separation of the volatile species from liquid phase were also crucial. The method of simultaneous determination of Zn and Cd by intermittent flow vapor generation led to the development of atomic fluorescence spectrometry. The detection limits (3σ_b) were 1.6 μg l⁻¹ for Zn and 0.01 μg l⁻¹ for Cd and the relative standard deviations were 3.6% for Zn (50 μg l⁻¹, n=11) and 1.7% for Cd (2 μg l⁻¹, n=11) respectively. Results for the determination of Zn and Cd have been confirmed by the analysis of CRMs with good agreement between the certified and found values.     

Purge efficiency in the determination of trihalomethanes in water by purge-and-trap gas chromatography

Purge-and-trap gas chromatography-mass spectrometry (PT-GC-MS) has become an accepted method for the analysis of trihalomethanes (THMs) in water. The purge-and-trap technique is based on an efficient transfer of volatile organic compounds from the liquid (contained in the purge chamber) to the gaseous phase by bubbling with an inert gas. The aim of this work was to study the purge system's efficiency by means of several consecutive purge cycles lasting 11 min each of the same liquid sample. The concentration range chosen of THMs was very wide [5-200 μg L⁻¹]. The inert gas flow rate was 40 mL min⁻¹, and experiments were performed at temperatures of 25, 35 and 50 °C. Bromoform (CHBr₃), the least volatile compound, needed 19 cycles to be purged quantitatively at a concentration of 200 μg L⁻¹ and only 7 cycles at 5 μg L⁻¹ for a 25 mL sample at 25 °C. Chloroform (CHCl₃), the most volatile compound, required 4 cycles to be fully extracted at 200 μg L⁻¹ and 2 at 5 μg L⁻¹. Finally, Novak's theoretical model, based on the distribution constant between gas and liquid phases, was used to correlate the THMs purging extraction data.     

2D spatiotemporal visualization system of expired gaseous ethanol after oral administration for real-time illustrated analysis of alcohol metabolism

A novel 2-dimensional spatiotemporal visualization system of expired gaseous ethanol after oral administration for real-time illustrated analysis of alcohol metabolism has been developed, which employed a low level light CCD camera to detect chemiluminescence (CL) generated by catalytic reactions of standard gaseous ethanol and expired gaseous ethanol after oral administration. First, the optimization of the substrates for visualization and the concentration of luminol solution for CL were investigated. The cotton mesh and 5.0 mmol L⁻¹ luminol solution were selected for further investigations and this system is useful for 0.1-20.0 mmol L⁻¹ of H₂O₂ solution. Then, the effect of pH condition of Tris-HCl buffer solution was also evaluated with CL intensity and under the Tris-HCl buffer solution pH 10.1, a wide calibration range of standard gaseous ethanol (30-400 ppm) was obtained. Finally, expired air of 5 healthy volunteers after oral administration was measured at 15, 30, 45, 60, 75, 90, 105 and 120 min after oral administration, and this system showed a good sensitivity on expired gaseous ethanol for alcohol metabolism. The peaks of expired gaseous ethanol concentration appeared within 30 min after oral administration. During the 30 min after oral administration, the time variation profile based on mean values showed the absorption and distribution function, and the values onward showed the elimination function. The absorption and distribution of expired gaseous ethanol in 5 healthy volunteers following first-order absorption process were faster than the elimination process, which proves efficacious of this system for described alcohol metabolism in healthy volunteers. This system is expected to be used as a non-invasive method to detect VOCs as well as several other drugs [1] in expired air for clinical purpose.     

Optical waveguide sensor of volatile organic compounds based on PTA thin film

In this study, a sensitive optical waveguide (OWG) sensor for the detection and identification of volatile organic compounds (VOCs) was reported. The sensing membrane is constructed by immobilization of peroxopolytungsten acid (PTA) thin film over a single-mode potassium ion (K⁺) exchanged glass OWG by spin-coating method. A laser beam was coupled into and out of the glass optical waveguide using prism couplers, and dry air functioned as a carrier gas. The sensor was tested for various volatile organic compounds (VOCs), and it showed higher response to the chlorobenzene gas compared to other VOCs. Therefore, we used the OWG sensor to detect chlorobenzene gas as a typical example of VOCs. The sensor exhibits a linear response to chlorobenzene gas in the range of 0.4-1000 ppm with rapid response and good reversibility. The constructed sensor is easy to fabricate and it has some unique qualities which can be characterized as inexpensive, sensitive, and reusable.     

Mesoporous silicate MCM-48 as an enrichment medium for ambient volatile organic compound analysis

This study investigated the sorption/desorption properties of MCM-48 and its applicability as a sorbent for on-line gas chromatographic analysis of ambient volatile organic compounds (VOCs). To establish a valid comparison, commercially available carbon sorbents were evaluated under similar analytical conditions. Two trapping temperatures of 30 °C and −20 °C, representing ambient and sub-ambient temperatures, were tested by trapping a full range of VOCs from C₂–C₁₂. At ambient temperatures, due to the mesoporosity, the MCM-48 showed considerably limited trapping efficiency compared to microporous carbon sorbents on the highly volatile section of VOCs and only began to show effective trapping for compounds larger than C₇. Cooling to sub-ambient temperatures (e.g., −20 °C) extended the effective trapping down to C₄ VOCs, drastically increasing the applicability of MCM-48 as an in-line enrichment medium for gas chromatographic analysis of VOCs. The mesoporosity of MCM-48 also aided desorption. Much lower desorption temperatures (100–180 °C) were required for full desorption as compared to the temperatures (greater than 200 °C) required for carbon sorbents. Moreover, the easy desorption was accompanied by a low memory effect, as the large pores of MCM-48 can clean up more efficiently after desorption, with little residue left behind.     

Determination of volatile organic compounds in urban and industrial air from Tarragona by thermal desorption and gas chromatography-mass spectrometry

This study describes the optimisation of an analytical method to determine 54 volatile organic compounds (VOCs) in air samples by active collection on multisorbent tubes, followed by thermal desorption and gas chromatography-mass spectrometry. Two multisorbent beds, Carbograph 1/Carboxen 1000 and Tenax/Carbograph 1TD, were tested. The latter gave better results, mainly in terms of the peaks that appeared in blank chromatograms. Temperatures, times and flow desorption were optimised. Recoveries were higher than 98.9%, except methylene dichloride, for which the recovery was 74.9%. The method's detection limits were between 0.01 and 1.25 μg m⁻³ for a volume sample of 1200 ml, and the repeatability on analysis of 100 ng of VOCs, expressed as relative standard deviation for n = 3, was lower than 4% for all compounds. Urban and industrial air samples from the Tarragona region were analysed. Benzene, toluene, ethylbenzene and xylenes (BTEX) were found to be the most abundant VOCs in urban air. Total VOCs in urban samples ranged between 18 and 307 μg m⁻³. Methylene chloride, 1,4-dichlorobenzene, chloroform and styrene were the most abundant VOCs in industrial samples, and total VOCs ranged between 19 and 85 μg m⁻³.     

Optimisation of solid-phase microextraction combined with gas chromatography-mass spectrometry based methodology to establish the global volatile signature in pulp and skin of Vitis vinifera L. grape varieties

The volatiles (VOCs) and semi-volatile organic compounds (SVOCs) responsible for aroma are mainly present in skin of grape varieties. Thus, the present investigation is directed towards the optimisation of a solvent free methodology based on headspace-solid-phase microextraction (HS-SPME) combined with gas chromatography-quadrupole mass spectrometry (GC-qMS) in order to establish the global volatile composition in pulp and skin of Bual and Bastardo Vitis vinifera L. varieties. A deep study on the extraction-influencing parameters was performed, and the best results, expressed as GC peak area, number of identified compounds and reproducibility, were obtained using 4 g of sample homogenised in 5 mL of ultra-pure Milli-Q water in a 20 mL glass vial with addition of 2 g of sodium chloride (NaCl). A divinylbenzene/carboxen/polydimethylsiloxane fibre was selected for extraction at 60 °C for 45 min under continuous stirring at 800 rpm. More than 100 VOCs and SVOCs, including 27 monoterpenoids, 27 sesquiterpenoids, 21 carbonyl compounds, 17 alcohols (from which 2 aromatics), 10 C₁₃ norisoprenoids and 5 acids were identified. The results showed that, for both grape varieties, the levels and number of volatiles in skin were considerably higher than those observed in pulp. According to the data obtained by principal component analysis (PCA), the establishment of the global volatile signature of grape and the relationship between different part of grapes—pulp and skin, may be an useful tool to winemaker decision to define the vinification procedures that improves the organoleptic characteristics of the corresponding wines and consequently contributed to an economic valorization and consumer acceptance.     

Organic vapour sensing using localized surface plasmon resonance spectrum of metallic nanoparticles self assemble monolayer

The response of localized surface plasmon resonance (LSPR) spectra of gold and silver nanoparticles, and gold nanoshells to organic vapors was investigated. The surface area of nanomaterials was sufficiently high for quantitative adsorption of volatile organic compounds (VOCs). Surface adsorption and condensation of VOCs caused the environmental refractive index to increase from n = 1.00 in pure air to as high as n = 1.29 in near saturated toluene vapor. The extinction and wavelength shift of the LSPR spectra were very sensitive to changes in the surface refractive index of the nanoparticles. Responses of the LSPR band were measured with a real-time UV-vis spectrometer equipped with a CCD array detector. The response of silver nanoparticles to organic vapors was most sensitive in changes in extinction, while gold nanoshells exhibited red-shifts in wavelength (∼250 nm/RIU) when exposed to organic vapors. The LSPR spectral shifts primarily were determined by the volatility and refractive indices of the organic species. The T₉₀ response time of the VOC-LSPR spectrum was less than 3 s and the response was completely reversible and reproducible.     

Comparative analysis of the volatile fraction from Annona cherimola Mill. cultivars by solid-phase microextraction and gas chromatography-quadrupole mass spectrometry detection

The analysis of volatile compounds in Funchal, Madeira, Mateus and Perry Vidal cultivars of Annona cherimola Mill. (cherimoya) was carried out by headspace solid-phase microextraction (HS-SPME) combined with gas chromatography-quadrupole mass spectrometry detection (GC-qMSD). HS-SPME technique was optimized in terms of fibre selection, extraction time, extraction temperature and sample amount to reach the best extraction efficiency. The best result was obtained with 2 g of sample, using a divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) fibre for 30 min at 30 °C under constant magnetic stirring (800 rpm).After optimization of the extraction methodology, all the cherimoya samples were analysed with the best conditions that allowed to identify about 60 volatile compounds. The major compounds identified in the four cherimoya cultivars were methyl butanoate, butyl butanoate, 3-methylbutyl butanoate, 3-methylbutyl 3-methylbutanoate and 5-hydroxymethyl-2-furfural. These compounds represent 69.08 ± 5.22%, 56.56 ± 15.36%, 56.69 ± 9.28% and 71.82 ± 1.29% of the total volatiles for Funchal, Madeira, Mateus and Perry Vidal cultivars, respectively. This study showed that each cherimoya cultivars have 40 common compounds, corresponding to different chemical families, namely terpenes, esters, alcohols, fatty acids and carbonyl compounds and using PCA, the volatile composition in terms of average peak areas, provided a suitable tool to differentiate among the cherimoya cultivars.     

Optimization of microwave-assisted solvent extraction for volatile organic acids in tobacco and its comparison with conventional extraction methods

In the present study, a new method using microwave-assisted solvent extraction (MASE) technique followed directly GC analysis was developed for the extraction of volatile organic acids (VOAs) in tobacco. The MASE conditions (heating time, volume of extracting solvent and extraction temperature) were optimized by means of an orthogonal array design (OAD) procedure. The results suggested that extractant, temperature and heating time were statistically the most significant factors. The extracts were directly analyzed with capillary GC operating in splitless-injection mode on an Agilent HP-FFAP capillary column. Under optimum operating conditions, MASE showed significantly better recoveries than those obtained by the conventional extraction method (ultrasonic and reflux extraction), ranging from 90.6% to 103.2%. In addition, a drastic reduction of the extraction time (20 min versus 4 h) and solvent consumption (20 mL versus 100 mL) was achieved with an outstanding reproducibility (CV ≤5%).     

Bacteria detection based on the evolution of enzyme-generated volatile organic compounds: Determination of Listeria monocytogenes in milk samples

The rapid detection of Listeria monocytogenes contamination in food is essential to prevent food-borne illness in humans. The aim of this study was to differentiate non-contaminated milk from milk contaminated with L. monocytogenes using enzyme substrates coupled with the analysis of volatile organic compounds (VOCs). The method is based on the activity of β-glucosidase and hippuricase enzymes and the detection of a specific VOC i.e. 2-nitrophenol and 3-fluoroaniline, respectively. VOCs were extracted, separated and detected by headspace-solid phase microextraction coupled to gas chromatography–mass spectrometry (HS-SPME GC–MS). This approach required the inclusion of the selective agent's cycloheximide, nalidixic acid and acriflavine HCl in the growth medium to inhibit interfering bacteria. The VOCs were liberated by L. monocytogenes provided that samples contained at least 1–1.5 × 10² CFU ml⁻¹ of milk prior to overnight incubation. This approach shows potential for future development as a rapid method for the detection of L. monocytogenes contaminated milk.     

Determination of terpenoids in wines by solid phase extraction and gas chromatography

A new method for determination of volatile terpenoids in wine is proposed. An off-line solid phase extraction—gas chromatographic method has been used for the determination. The influence of several extraction variables was studied, including the solid phase employed (C-18 versus divinylbenzene-based), eluting solvent (n-pentane, dichloromethane, ethanol and methanol), volume of eluting solvent (1-4 ml) and drying time (0-20 min). Complete recovery of volatile terpenoids from several kinds of wines was obtained under the optimized conditions.     

A new cataluminescence gas sensor based on SiO2 nanotubes fabricated using carbon nanotube templates

In the present work, two morphologies of SiO₂ nanomaterials (SiO₂ nanotubes and nanoparticles) have been successfully synthesized in supercritical fluids (SCFs). The cataluminescence (CTL) features of the two SiO₂ nanomaterials to some common harmful gases were compared, and the results showed that SiO₂ nanotubes had better CTL sensing characteristic to some common harmful gases. The SiO₂ nanotubes not only had uniform size and shape with a high specific surface area, but also exhibited superior sensitivity and selectivity to ethyl acetate vapor. Using the SiO₂ nanotubes as sensing material, a CTL sensor for ethyl acetate vapor was developed. The proposed sensor showed high sensitivity and specificity to ethyl acetate at optimal temperature of 293 °C, a wavelength of 425 nm and a flow rate of 345 mL/min. With a detection limit of 0.85 ppm, the linear range of CTL intensity versus concentrations of ethyl acetate vapor was 2.0-2000 ppm. None or only very low levels of interference were observed while the foreign substances such as acetone, acetaldehyde, acetic acid, formaldehyde, ammonia, ethanol, benzene and methanol were passing through the sensor. This method allows rapid determination of gaseous ethyl acetate at workshop.