Direct Thermal Desorption-gas Chromatography-mass Spectrometry Research Articles

Profiling of Organosulfur Compounds in Onions: A Comparative Study between LC-HRMS and DTD-GC-MS

Onions are known not only for their culinary importance but also for their nutritional and health-promoting properties. Both properties are closely linked to their content of organosulfur compounds, which account for up to 5% of the dry weight of an onion. Given the importance of these compounds, suitable analytical methods are required for their study. Two techniques should be highlighted in this context: gas chromatography coupled to mass spectrometry (GC-MS), and liquid chromatography coupled to mass spectrometry (LC-MS). In this study, eight different onion varieties were analyzed using two distinct analytical techniques: direct thermal desorption–gas chromatography–mass spectrometry (DTD-GC-MS) and high-resolution mass spectrometry (HRMS) on an LC-ESI-QqTOF instrument. Each method identified different organosulfur compounds, with LC-HRMS targeting 15 non-volatile compounds, such as cysteine sulfoxides, and GC-MS targeting 18 volatiles, such as disulfides and trisulfides. The results obtained were studied using Pearson correlations and principal component analysis. No precise correlation was found between the initial organosulfur compounds in onions and their hydrolysates. Consequently, although GC is one of the most employed techniques in the scientific literature, the use of LC-HRMS or a combination of both techniques may offer a more comprehensive and accurate description of the metabolomic profile of onions.

Measuring aliphatic hydrocarbons in sediments by direct thermal desorption-gas chromatography-mass spectrometry: Matrix effects and quantification challenges

Direct sample introduction thermal desorption (TD) coupled to GC–MS was investigated for the analysis of paraffinic hydrocarbons (HCs) from polluted sediments. TD-GC–MS is sometimes used for analysing paraffinic HCs from atmospheric particles but rarely for their direct desorption from sediments. So, the new TD methodology, applied to sediments, required development, optimization and validation. A definitive screening experimental design was performed to discriminate the critical factors on TD efficiency, from model sediments containing various organic matter (OM) amounts. Low molecular weight HCs had extraction behaviours markedly different from high molecular ones (HMW-HCs), but a compromise was found using very few sediment amount (5 mg), high temperature rate (55 °C min−1) and final temperature (350 °C). Linear HCs (n-C10 to n-C40) could be quantified using the matrix-matched calibration method, with very low detection limits (3.8–13.4 ng). The amount of the overall paraffinic alkanes was also determined as a sum of unresolved components between predefined equivalent carbon ranges. The developed solventless methodology was compared to an optimized solvent microwave assisted extraction (MAE). Matrix effects could be higher for TD compared to MAE but it depended on sediment matrix. When matrix effect was strong, particularly on HMW-HCs signal depletion, a dilution with pure non-porous sand was favourable for accurate quantification. The sum of resolved and unresolved HCs gave comparable results between MAE and TD extractions, with an exception of alkanes greater than C30 which were less quantitatively extracted via TD. However, TD-GC–MS was more sensitive than MAE-GC–MS. So TD-GC–MS is useful for analyzing sediments containing a great range of paraffinic HCs (C9-C34) and it has the advantages of being fully automated, with few sample preparation and operator intervention, using very low amounts of solvent, and generating few wastes.

Application of Direct Thermal Desorption-Gas Chromatography-Mass Spectrometry for Determination of Volatile and Semi-Volatile Organosulfur Compounds in Onions: A Novel Analytical Approach.

The population is now more aware of their diets due to the connection between food and general health. Onions (Allium cepa L.), common vegetables that are minimally processed and grown locally, are known for their health-promoting properties. The organosulfur compounds present in onions have powerful antioxidant properties and may decrease the likelihood of developing certain disorders. It is vital to employ an optimum approach with the best qualities for studying the target compounds to undertake a thorough analysis of these compounds. In this study, the use of a direct thermal desorption-gas chromatography-mass spectrometry method with a Box-Behnken design and multi-response optimization is proposed. Direct thermal desorption is an environmentally friendly technique that eliminates the use of solvents and requires no prior preparation of the sample. To the author's knowledge, this methodology has not been previously used to study the organosulfur compounds in onions. Likewise, the optimal conditions for pre-extraction and post-analysis of organosulfur compounds were as follows: 46 mg of onion in the tube, a desorption heat of 205 °C for 960 s, and a trap heat of 267 °C for 180 s. The repeatability and intermediate precision of the method were evaluated by conducting 27 tests over three consecutive days. The results obtained for all compounds studied revealed CV values ranging from 1.8% to 9.9%. The major compound reported in onions was 2,4-dimethyl-thiophene, representing 19.4% of the total area of sulfur compounds. The propanethial S-oxide, the principal compound responsible for the tear factor, accounted for 4.5% of the total area.

Chemical characterization of Brazilian propolis using automated direct thermal desorption-gas chromatography-mass spectrometry.

Propolis, produced by honey bees, is used around the world, displaying several corroborated biological activities. Brazil is one of the leading producers of propolis, with a great diversity of types, each with a characteristically chemical fingerprint influenced by the flora of the local region. The secondary metabolite's composition of propolis strongly impacts its biological properties, and its chemical characterization is of great importance for its quality control. Several chromatographic techniques have been applied to characterize propolis, highlighting the extraction of its volatiles and its analysis through gas chromatography. Fourteen Brazilian propolis samples collected in four states, including brown, green and red propolis types, were chemically characterized using the automated direct thermal desorption-gas chromatography-mass spectrometry (DTD-GC-MS). Red propolis type was characterized by acyclic saturated hydrocarbons, fatty alcohols, terpenes, and phenylpropanoids as nonacosane, α-copaene, β-amyrin acetate, anethole, and 7-O-methylvestitol. Brown propolis presented hydrocarbons, monoterpenes, and sesquiterpenes, as α-pinene and α-bisabolol. Brazilian green propolis presented polycyclic aromatic hydrocarbons and sesquiterpenes, including 1-methyl-octahydroanthracene, 2,5-dimethyl-γ-oxo-benzenebutanoic acid, nerolidol, and spathulenol. Principal component analysis (PCA) was performed, allowing for clustering brown and red propolis types, indicating a divergence with the chemical composition of the green propolis samples. The hierarchical cluster analysis (HCA) allowed the chemical fingerprint of each propolis type to be differentiated. Red propolis was characterized by sesquiterpenes, pterocarpans, and isoflavans; brown propolis was characterized by hydrocarbons, aldehydes, and monoterpenes, while green propolis samples were characterized by the presence of polycyclic aromatic hydrocarbons, sesquiterpenes, and naphthalene derivatives. © 2022 Society of Chemical Industry.

Uptake and Release of Aroma Compounds by an Ethylene Propylene Diene Monomer Rubber Sealing Polymer: Investigating Aroma Carryover in a Model Wine System.

Aromatized wines and regular table wines are often filled on the same bottling line. Sealing polymers in the filling line absorb volatiles from aromatized wines and may migrate due to insufficient cleaning into the subsequently bottled regular wine. Unintentional carryover of volatiles may lead to accusation of illegal aromatization of wine. Absorption, cleaning efficacy, and migration of volatiles into ethylene propylene diene monomer rubber were investigated in a model system. Direct thermal desorption-gas chromatography-mass spectrometry analysis of seven aroma compounds monitored variation in the polymer (μg/g). Absorption of volatiles was mostly driven by their octanol/water partition coefficients. Cleaning of polymers removed 11 to 62% of the absorbed volatiles. Subsequent immersion of cleaned polymers into model wine revealed migration of 20 to 57% of the remaining volatiles. Sensory tests suggested the impact of transferred volatiles into subsequent model wine. For α-ionone, an odor activity value of 1.03 indicated a potential sensory impact.

Characterization of the Aromatic and Phenolic Profile of Five Different Wood Chips Used for Ageing Spirits and Wines.

Wooden barrels and wood chips are usually used in the ageing of spirits and wines to improve their sensorial profile. Oak wood is the most popular material used in cooperage, but there are other interesting woods, such as cherry or chestnut, that could be considered for this purpose. In this study, a novel method for the determination of the aromatic profile of wood powder by Direct Thermal Desorption-Gas Chromatography-Mass Spectrometry (DTD-GC-MS) was optimized by experimental design. The volatile composition of five different types of wood chips was determined by direct analysis of wood powder by DTD-GC-MS method developed. Thirty-one compounds from wood were identified through this analysis, allowing the differentiation between woods. The aromatic and phenolic compound profile of the 50% hydroalcoholic extract of each type of wood studied was analyzed by Stir-bar Sorptive Extraction-Gas Chromatography-Mass Spectrometry (SBSE-GC-MS) and Ultra-High-Performance Liquid Chromatography (UHPLC) to determine which wood compounds are transferred to spirits and wine after ageing. Different phenolic profiles were found by UHPLC in each wood extract, allowing their differentiation. However, results obtained by SBSE-GC-MS did not allow distinguishing between wood extracts. The analysis of wood in solid state, without any type of previous treatment except grinding, by DTD-GC-MS does not imply any loss of information of the aromatic compounds present in wood as other techniques. This is a potential method to identify aromas in wood that, in addition, allows different types of wood to be differentiated.

A comparison of direct thermal desorption with solvent extraction for gas chromatography-mass spectrometry analysis of semivolatile organic compounds in diesel particulate matter

Direct thermal desorption-gas chromatography-mass spectrometry (DTD-GC-MS) is a technique that is finding application in the characterisation of the semivolatile organic carbon fraction of ambient and combustion source particulate matter (PM) collected on filters. In this study, three DTD-GC-MS methods were assessed and compared to a conventional solvent extraction method for analysis of a mixture of target analytes in solution and of diesel PM collected on quartz filters. The target analytes included n-alkanes, hopanes, steranes and polycyclic aromatic hydrocarbons. This study showed that while the three DTD-GC-MS methods were generally comparable to the solvent extraction method, (1) the choice of calibration strategy and calibration materials has a significant impact on the measured accuracy of a method; (2) very large variations were seen in all methods for the more volatile compounds such as C10 to C13 n-alkanes and naphthalene; (3) accuracy, defined as difference from the known concentration of a liquid sample, ranged from 5% to 32%; (4) precision, defined as the relative standard deviation, ranged from 4% to 16%. The average difference of DTD-GC-MS results from the solvent extraction results for the diesel PM filters ranged from 20% to 40%. This difference was driven by the large number of target analytes present at relatively low concentrations (<25 pg/mm2) and their corresponding higher variability. Differences in performance among the compound classes were noted. Minimum detection limits for the DTD-GC-MS methods were on the order of 0.1 to 1 pg/mm2 and were as good as or better than those obtained for the solvent extraction method.

Investigations into a novel method for atmospheric polycyclic aromatic hydrocarbon monitoring

A novel analytical method for atmospheric polycyclic aromatic hydrocarbons (PAHs) was developed based on laser induced fluorescence (LIF) of samples on quartz multi-channel polydimethylsiloxane traps. A tunable dye laser with a frequency doubling crystal provided the excitation radiation, and a double monochromator with a photomultiplier tube detected emitted fluorescence. The method allowed for the rapid (<5 min), cost effective analysis of samples. Those yielding interesting results could be further analysed by direct thermal desorption-gas chromatography–mass spectrometry (TD–GC–MS, with limits of detection of ∼0.3 ng m −3), as photodegradation was minimal (<10% over 5 min irradiation). Small amounts of naphthalene photodegradation products identified by TD–GC–MS after >15 min irradiation, included phenol, benzyl alcohol and phthalic anhydride. Without any signal optimization, a LIF detection limit of ∼1 μg m −3 was established for naphthalene using a diffusion tube (diffusion rate of 2 ng s −1) and 292 nm excitation.

Identification of a hydroxy substituted calamenene—a sesquiterpene associated with wound reactions in non-infected xylem of Tilia spp.

Xylem of lime trees ( Tilia spp.) with wound reactions was structurally investigated by scanning (SEM) and transmission electron microscopy (TEM) as well as chemically analyzed by direct thermal desorption-gas chromatography–mass spectrometry (DTD-GC–MS). Wound reactions in the outer xylem lead to distinct discolourations around the wound. Within a 4-week response no fungal infection occurred in discoloured xylem. At the fine structural level, wound reactions become primarily visible as the secretion of dark-staining substances from parenchyma cells into lumens of vessels and fibres. With increasing reaction time vessels aggregate large amounts of secretion products, whereas in fibres wall-associated linings are formed and the inner secondary wall appears incrusted. After 2–3 months a narrow, greenish-brown boundary developed at the transition between the discoloured outer and the unchanged inner xylem. This green-brown boundary layer remained non-infected also in older wounds. DTD-GC–MS analyses revealed that the sesquiterpene Hydroxycalamenene represents a key substance of wound reactions in non-infected lime trees. Other substances such as fatty acids or their esters and coniferyl aldehydes or their derivatives were also found. TEM investigations of the samples after DTD-GC–MS showed less pronounced cell wall-attached linings in fibres as well as reduced incrustation of inner secondary walls. The massive deposits in the vessel lumens remained unchanged. The role of these wound reaction products and their ways of synthesis are discussed.

Automated liner exchange— A novel approach in direct thermal desorption— gas chromatography

A system was developed for fully automated liner exchange in direct thermal desorption— gas chromatography— mass spectrometry (DTD-GC-MS). Samples are put into a newly developed liner which is capped with a standard crimp cap. The liners are placed in a sample tray and transported to the thermal desorption device. Both liner transport and liner exchange (which can be performed after each analysis) are automated. The system was tested for spores and pollen, vegetable oil, wood (preservative), car exhaust (BTEX), and tobacco (nicotine) analysis to demonstrate the robustness and flexibility of the approach.

Analyses of the wood preservative component N-cyclohexyl-diazeniumdioxide in impregnated pine sapwood by direct thermal desorption–gas chromatography–mass spectrometry

Investigations concerning the qualitative and quantitative determination of the organic wood preservative component N-cyclohexyl-diazeniumdioxide (HDO) in treated timber were carried out by means of direct thermal desorption–gas chromatography–mass spectrometry (DTD–GC–MS). It could be shown that the identification of HDO in treated pine sapwood ( Pinus sylvestris L.) is relatively simple using this analytical technique. Quantification of this active ingredient can be carried out using the peak area of the specific mass fragment m/ z 114. A calibration curve with a high correlation coefficient was obtained in the range from 40 to 550 mg HDO per kg timber. Furthermore it can be deduced that the results obtained are characterised by an excellent reproducibility with standard deviations ranging from 5 to 10% in general. For the chosen experimental set up a detection limit of 4 mg HDO per kg treated pine sapwood was calculated, although merely 20% of the active ingredient was desorbed.

Direct thermal desorption-gas chromatography and gas chromatography-mass spectrometry profiling of hop (Humulus lupulus L.) essential oils in support of varietal characterization.

The use of direct thermal desorption-gas chromatography-mass spectrometry (DTD-GC-MS) and DTD-GC-flame ionization detection (DTD-GC-FID) for characterization of hop essential oils is described. Four hop varieties (Nugget, Galena, Willamette, and Cluster) from the Yakima valley (Yakima, WA) 1998 harvest were analyzed by DTD-GC-MS and DTD-GC-FID methodology. Approximately 1 g of hops was needed for the analysis. Hop samples were prepared for GC-MS and/or GC-FID profiling in approximately 20 min. More than 100 volatile compounds have been identified and quantified for each hop variety. The results were found to be in good agreement with conventional steam distillation-extraction (SDE) data. A calibration curve for determination of essential oil content in hops by DTD-GC-FID has been generated. Quantitation of hop oil content by DTD-GC-FID was shown to be in good agreement with conventional SDE data. The recovery of key oil components valuable for varietal identification was demonstrated to be highly reproducible and characteristic of each variety analyzed when DTD-GC-FID was used for analysis.

Analysis of volatile components of oak wood by solvent extraction and direct thermal desorption-gas chromatography-mass spectrometry

Volatile compounds with important sensory properties ( cis- and trans-ß-methyl-γ-octalactone, eugenol, vanillin and syringaldehyde) present in oak woods have been studied. Two analytical methods have been compared: GC-MS analysis of wood hydroalcoholic extracts, and direct thermal desorption (DTD)-GC-MS in the selective ion monitoring mode. Although the quantitative results obtained from the two methods were comparable, the DTD based method is of considerable interest since woods of different origins can be discriminated rapidly from the ratio of the two oak lactone isomer concentrations, using a small (20 mg) sample size.

Characterization of powdered turmeric by liquid chromatography-mass spectrometry and gas chromatography-mass spectrometry

Five commercial powdered turmeric samples were analyzed to identify major and minor components. The developed HPLC method allows the separation of curcumin, demethoxycurcumin and bisdemethoxycurcumin, as well as three other major components and numerous minor components. The separation was accomplished on an octadecyl stationary phase using a mobile phase consisting of 50 m M ammonium acetate with 5% acetic acid and acetonitrile as the organic modifier. Thermospray mass spectra were obtained for all of the components. Particle beam EI-mass spectra were obtained for the curcuminoids, but could not be obtained for the other components due to the limitations of the particle beam interface when analyzing volatile and semi-volatile compounds. EI mass spectra for the volatile components were obtained by direct thermal desorption-gas chromatography-mass spectrometry (DTD-GC-MS).