Assessment of physicochemical properties of sorbent materials in passive and active sampling systems towards gaseous nitrogen-containing compounds.

The adsorption and desorption behavior of volatile nitrogen-containing compounds in vapor phase by solid-phase microextraction Arrow (SPME-Arrow) and in-tube extraction (ITEX) sampling systems, were investigated experimentally using gas chromatography-mass spectrometry. Three different SPME-Arrow coating materials, DVB/PDMS, MCM-41, and MCM-41-TP and two ITEX adsorbents, TENAX-GR and MCM-41-TP were compared to clarify the selectivity of the sorbents towards nitrogen-containing compounds. In addition, saturated vapor pressures for these compounds were estimated, both experimentally and theoretically. In this study, the adsorption of nitrogen-containing compounds on various adsorbents followed the Elovich model well, while a pseudo-first-order kinetics model best described the desorption kinetics. Pore volume and pore sizes of the coating sorbents were essential parameters for the determination of the adsorption performance for the SPME-Arrow sampling system. MCM-41-TP coating with the smallest pore size gave the slowest adsorption rate compared to that of DVB/PDMS and MCM-41 in the SPME-Arrow sampling system. Both adsorbent and adsorbate properties, such as hydrophobicity and basicity, affected the adsorption and desorption kinetics in SPME-Arrow system. The adsorption and desorption rates of studied C6H15N isomers in the MCM-41 and MCM-41-TP sorbent materials of SPME-Arrow system were higher for dipropylamine and triethylamine (branched amines) than for hexylamine (linear chain amines). DVB/PDMS-SPME-Arrow gave fast adsorption rates for the aromatic-ringed pyridine and o-toluidine. All studied nitrogen-containing compounds demonstrated high desorption rates with DVB/PDMS-SPME-Arrow. Chemisorption and physisorption were the sorption mechanisms in MCM-41- and MCM-41-TP- SPME-Arrow, but additional experiments are needed to confirm this. An active sampling technique ITEX gave comparable adsorption and desorption rates on the selective MCM-41-TP and universal TENAX-GR sorbent materials for all the compounds studied. Vapor pressures of nitrogen-containing compounds were experimentally estimated by using retention index approach and these values were compared with the theoretical ones, calculated using the COnductor-like Screening MOdel for Real Solvent (COSMO-RS) model. Both values agreed well with those found in the literature proving that these methods can be successfully used in predicting VOC's vapor pressures, e.g. for the formation of secondary organic aerosols.

In-tube dynamic extraction for analysis of volatile organic compounds in honey samples.

Honey is the oldest and nowadays widely used natural sweetener for food worldwide. Its composition is associated with its botanical and geographical origin and honey is often mislabeled and has a high potential for food fraud. Thus, quick easy and sensitive analyses are required. For the first time, we developed and applied an automated, fast, sensitive and robust, in-tube extraction dynamic headspace in-tube extraction-dynamic headspace (ITEX-DHS) method for a variety of Honey containing VOCs in connection with GC-MS. Another advantage of ITEX is, that it is a green analytical solventless method. The method provides very low method detection limits (MDL) from 0.8 to 47 ng g-1 for VOCs in honey samples as well as very good repeatabilities with averages below 9 % RSD. Recoveries are between 83 and 100 %. Only octanal possess a repeatability 13 % and a recovery of 62 % due to its high polarity. 38 honey samples were measured after method validation. Four acacia honeys (A), six forest honeys (F) and 22 blossom honeys (B). The type of six honeys was not known (U) but could be predicted with the help of a linear discriminant analysis (LDA). The LDA was carried out with the three groups (A, B, F) leading to a proportion of correct predictions of 90.6 %. With the help of a scatterplot, two of the unknown samples were classified as forest honeys and four of them as blossom honeys.

Quantitative analysis and spatial and temporal distribution of volatile organic compounds in atmospheric air by utilizing drone with miniaturized samplers.

Our second generation air sampling drone system, allowing the simultaneous use of four solid phase microextraction (SPME) Arrow and four in-tube extraction (ITEX) units, was employed for collection of atmospheric air samples at different spatial and temporal dimensions. SPME Arrow coated with two types of materials and ITEX with 10% polyacrylonitrile as sorbent were used to give a more comprehensive chemical characterization of the collected air samples. Before field sampling, miniaturized samplers went through quality control and assurance in terms of reproducibility (RSD ≤14.1%, N = 4), equilibrium time (≥10 min), breakthrough volume (1.8 L) and storage time (up to 48 h). 128 air samples were collected under optimal sampling conditions from July to September 2019 at the SMEAR II station and Qvidja farm, Finland. 347 VOCs were identified in the air samples either on-site or in the laboratory by thermal desorption gas chromatography - mass spectrometry, and they were quantified/semiquantified using Partial Least Squares Regression models. Individual models were developed for the different coatings and packing materials using gas phase standards obtained by an automatic permeation system. Average gas phase VOC concentrations ranged from 0.1 (toluene, the SMEAR II station) to 680 ng L-1 (acetone, Qvidja farm). Average VOC concentrations in aerosols ranged from 0.1 (1,4-cyclohexadiene, the SMEAR II station) to 2287 ng L-1 (megastigma-4,6,8-triene, Qvidja farm). Clear differences in results were seen for samples collected at the SMEAR II station and Qvidja farm, between VOC compositions in gas phase and aerosols, and between the sampling site and height.

A green approach for the extraction of diamondoids from petroleum source rock.

Extraction of adamantanes and diamantanes from petroleum source rock using nonionic surfactant was investigated and the optimum conditions for yields of the diamondoids were determined. The conventionally used accelerated solvent extraction method was compared to an innovative microwave-assisted nonionic surfactant extraction (MANSE). A three-level full factorial design of experiment (DoE) was adopted for the optimization of MANSE, involving solvent concentration, extraction temperature as well as extraction time. In-tube extraction (ITEX-2) using TENAX TA as sorbent in combination with gas chromatography-mass spectrometry (GC-MS) was used to determine the diamondoids in the extract. The results revealed that solvent concentration, extraction temperature and time have significant effects on extraction yields of the diamondoids. 0.04 M was the optimum surfactant concentration for extraction of both, adamantane and diamantane. The highest yields of the diamondoids were obtained at extraction temperature of 80 °C. The optimum extraction time for both adamantane and diamantane was 10 min. In comparison with the accelerated solvent extraction method, the results showed that MANSE is more efficient. This study has revealed that MANSE is a robust and efficient environmentally benign sample preparation method for geochemical evaluation of petroleum source rock.

Development and performance evaluation of a novel dynamic headspace vacuum transfer "In Trap" extraction method for volatile compounds and comparison with headspace solid-phase microextraction and headspace in-tube extraction.

Headspace in-tube extraction (HS-ITEX) and solid phase microextraction (HS-SPME) sampling, followed by gas chromatography-mass spectrometry (GC-MS), are widely used to analyze volatile compounds in various food matrices. While the extraction efficiency of volatile compounds from foodstuffs is crucial for obtaining relevant results, these efficiency of these extraction methods limited by their long extraction times and requirements for large sample quantity. This study reports on the development and application of a new extraction technique based on HS-ITEX hardware, which improves the extraction rate and capacity by operating under reduced pressure, called Dynamic Headspace Vacuum Transfer In-Trap Extraction (DHS-VTT). The results of the study indicate that DHS-VTT improves the extraction of the target compounds. The area of the mass spectrometer signal for each compound can be up to 450 times more intense than the HS-SPME and HS-ITEX techniques performed in the same experimental conditions of extraction temperature and time. DHS-VTT runs in automated mode, making it possible to work with smaller sample quantity and also favors the HS extraction of all volatile compounds. In addition, the necessary modifications to the installation were cheap and the life of an ITEX trap is up to 10 times longer than an SPME fibre.

Needle-based extraction techniques with protected sorbent as powerful sample preparation tools to gas chromatographic analysis: Trends in application.

Microextraction techniques are widely applied for sample preparation to gas chromatographic analysis of target compounds in samples with a complex matrix. Recently, needle-based microextraction techniques have been developed in order to improve performance of the extraction. The main advantages of these techniques are miniaturization, automation, high performance, environmentally friendliness and on-line coupling with analytical instruments. This review focuses on the three needle-based microextraction techniques including solid-phase dynamic extraction (SPDE), in-tube extraction (ITEX) and needle trap device extraction (NTD). The core of the aforementioned techniques is an extraction phase protected in the stainless steel needle. The application of the sorbent-protected needle extraction techniques for the gas chromatographic analysis of environmental, biological and food samples is discussed. The fundamental aspects and development over the years are also summarized.

Sorbent material characterization using in-tube extraction needles as inverse gas chromatography column.

In-tube extraction is a full automated enrichment technique that consists of a stainless-steel needle, packed with sorbent material for the extraction of volatile and semivolatile compounds. In principle, all particulate sorbents used for enrichment in air or headspace analysis can be used. However, the selection of the sorbents is merely based on empirical considerations rather than on experimental data, which is caused by a lack of knowledge about the relevant physicochemical properties of the sorbent. Especially, the knowledge of hydrostatic, advective, diffusive, and dispersion mechanisms in addition to sorption enthalpies are important for combined transport and sorption models. To provide these missing parameters, we developed and evaluated a method in which an ordinary in-tube extraction needle was employed directly as column for sorbent characterization by inverse gas chromatography. As probe compounds, benzene, ethyl acetate, and 3-methyl-1-butanol were used to determine thermodynamic parameters such as sorption enthalpy, partitioning constant between the solid and gas phase, and kinetic parameters such as the diffusion coefficient, dispersion coefficient, and apparent permeability, exemplarily. As sorbent, three commercially available phases were characterized to demonstrate the applicability of the method.

In-tube extraction for the determination of the main volatile compounds in Physalis peruviana L.

An analytical procedure based on in-tube extraction followed by gas chromatography with mass spectrometry has been developed for the analysis of 24 of the main volatile components in cape gooseberry (Physalis peruviana L.) samples. According to their chemical structure, the compounds were organized into different groups: one hydrocarbon, one aldehyde, four alcohols, four esters, and 14 monoterpenes. By single-factor experiments, incubation temperature, incubation time, extraction volume, extraction strokes, extraction speed, desorption temperature, and desorption speed were determined as 60°C, 20 min, 1000 µL, 20, 50:50 µL/s, 280°C, 100 µL/s, respectively. Quantitative analysis using authentic standards and external calibration curves was performed. The limit of detection and limit of quantification for the analytical procedure were calculated. Results shown the benzaldehyde, ethyl butanoate, 2-methyl-1-butanol, 1-hexanol, 1-butanol, α-terpineol, and terpinen-4-ol were the most abundant volatile compounds in analyzed fruits (68.6-585 µg/kg). The obtained data may contribute to qualify cape gooseberry to the group of superfruits and, therefore, increase its popularity.

In-Tube Extraction-GC-MS as a High-Capacity Enrichment Technique for the Analysis of Alcoholic Beverages.

An in-tube extraction (ITEX) method for the GC-MS analysis of volatile constituents of alcoholic beverages was developed and applied in the analysis of 46 beers from six varieties, Alt, Helles, Kölsch, Pilsener beer, Schwarzbier, and wheat beer, which are popular in Germany. The extraction performance of nine different sorbent materials was evaluated. The best overall sensitivity was achieved using Tenax TA, with method detection limits down to 0.01 µg L-1, whereas the widest linear range was possible with PDMS, covering almost 5 orders of magnitude. This is the first application of PDMS in ITEX as a high-capacity extraction device and highlights the importance of choosing the appropriate sorbent material for the analytical task at hand. A satisfying chemometric discrimination of all analyzed beer varieties was possible, and alcohol-free beers could clearly be separated from regular beers, also.

Chemometric discrimination of different tomato cultivars based on their volatile fingerprint in relation to lycopene and total phenolics content.

INTRODUCTION: The characteristic flavour of tomato is given by a complex mixture of sugars, acids, amino acids, minerals and volatile metabolites. Of these, volatile compounds are considered to greatly influence the flavour of tomato fruits. The volatile aroma compounds and phytochemical content of tomatoes are dependent on genotype, environmental conditions and cultural practices, and can thus be used for cultivar discrimination. OBJECTIVE: To assess the possibility of using the volatile profile of tomato to fingerprint and discriminate different tomato cultivars based on an 'in-tube extraction' technique coupled to gas chromatography, combined with mass spectrometry (ITEX/GC-MS) and a chemometric approach. RESULTS: Using the ITEX/GC-MS technique, 61 volatiles were analysed and separated from tomato cultivars, with 58 being identified. The main volatiles identified in all tomato cultivars were: hexanal, trans-2-hexenal, 1-hexanol, 3-pentanone, 3-methylbutanol, 2-methylbutanol, 3-methylbutanal and 6-methyl-5-hepten-2-one. The lycopene content and total phenolic compound content of the tomato cultivars varied between 36.78 and 73.18 mg/kg fresh weight (fw) and from 119.4 to 253.7 mg of gallic acid equivalents (GAE) per kilogram fresh weight, respectively. Volatile fingerprint and phytochemical composition led to a good differentiation between tomato cultivars, with the first two principal components explaining 89% of the variance in the data. CONCLUSION: The tomato cultivars studied were easily discriminated based on their characteristic volatile profile that was obtained using the reliable ITEX/GC-MS technique. Principal component analysis revealed, in addition to volatile compounds, the important role played by the total phenolic content in tomato cultivar discrimination, which is highly correlated with phenotypic and biochemical differences between tomato cultivars.

Metabolic profiling of oxidized lipid-derived volatiles in blood by gas chromatography/mass spectrometry with in-tube extraction.

Once lipids are oxidized, various volatiles are produced by cleavage of the fatty acid side chain. Considering the variety of lipids present in the body, a large number of possible volatiles might originate from oxidized lipids. However, only specific volatiles such as aldehydes are exclusively examined in current studies, and there is no reported method for the exhaustive analysis of all volatiles. We developed a sensitive analytical method for the detection of all possible volatiles for multimarker profiling, applying a new extraction method called in-tube extraction. Oxidized phosphatidyl choline standards were prepared in vitro and analyzed in order to determine the potential variety of volatiles. Over 40 compounds, including alcohols, ketones, and furanones, were identified in addition to the aldehydes reported previously. Based on this result, we applied our analytical method to mouse plasma and identified 12 volatiles, including 1-octen-3-ol, which is correlated to disease states. To determine the volatile profile after oxidation, we oxidized plasma in vitro under various conditions and identified 27 volatiles, including 1-octen-3-ol and benzaldehyde. The generation capacity of each volatile was different. This method allows sensitive and exhaustive analysis of various volatiles in addition to aldehydes.