Direct Thermal Desorption Research Articles

DETECTION OF KNOWN PHOTOCHEMICAL DECOMPOSITION PRODUCTS OF PAH IN PARTICULATE MATTER FROM POLLUTION EPISODES IN SEOUL, KOREA

Over the past two decades, significant efforts have been expended to identify the photochemical decomposition products of the OH radical reactions of various polycyclic aromatic compounds (PAC), such as naphthalene, methylnaphthalenes, acenaphthene and phenanthrene (1, 2, 3, 4, 5, 6, 7). Although these parent PAC are predominantly found in the gas phase, many of their oxidation products have been found largely in the particle phase (4, 7, 8). These products include diones, hydroxy-, and nitrated products as well as many products resulting from ring-opening steps. It is, or should be, the goal of every laboratory study on atmospheric processes to apply the laboratory results to real world samples. To this end, we have obtained particulate matter air samples, as well as some smog episode samples, from Seoul Korea and have searched for the known decomposition products of the above mentioned PAC. To eliminate the use of chlorinated solvents used in the extraction and analysis of particulate matter samples, we have been utilizing the direct thermal desorption of small (4 mm diameter) punches of filters followed by Multidimensional Gas Chromatography-Time of Flight Mass Spectrometry (TD-GCxGC-TOFMS) for the analysis of the desorbed compounds. So far, we have detected 14 of the known decomposition products of naphthalene, acenaphthene and phenanthrene in the Seoul pollution episode samples. These include: 1-hydroxynaphthalene, (E) 2-formylcinnamaldehyde, phthalic anhydride, phthalide, 1,2-naphthalic anhydride, 9-hydroxyphenanthrene and dibenzopyrone.

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.

Dynamic Planar Solid Phase Microextraction−Ion Mobility Spectrometry for Rapid Field Air Sampling and Analysis of Illicit Drugs and Explosives

A preconcentration device that targets the volatile chemical signatures associated with illicit drugs and explosives (high and low) has been designed to fit in the inlet of an ion mobility spectrometer (IMS). This is the first reporting of a fast and sensitive method for dynamic sampling of large volumes of air using planar solid phase microextraction (PSPME) incorporating a high surface area for absorption of analytes onto a sol-gel polydimethylsiloxane (PDMS) coating for direct thermal desorption into an IMS. This device affords high extraction efficiencies due to strong retention properties at ambient temperature, resulting in the detection of analyte concentrations in the parts per trillion range when as low as 3.5 L of air are sampled over the course of 10 s (absolute mass detection of less than a nanogram). Dynamic PSPME was used to sample the headspace over the following: 3,4-methylenedioxymethamphetamine (MDMA) tablets resulting in the detection of 12-40 ng of piperonal, high explosives (Pentolite) resulting in the detection of 0.6 ng of 2,4,6-trinitrotoluene (TNT), and low explosives (several smokeless powders) resulting in the detection of 26-35 ng of 2,4-dinitrotoluene (2,4-DNT) and 11-74 ng of diphenylamine (DPA).

Bound Volatile Precursors in Genotypes in the Pedigree of ‘Marion’ Blackberry (RubusSp.)

Glycosidically bound volatiles and precursors in genotypes representing the pedigree for 'Marion' blackberry were investigated over two growing seasons. The volatile precursors were isolated using a C18 solid-phase extraction column. After enzymatic hydrolysis, the released volatiles were analyzed using stir bar sorptive extraction gas chromatography-mass spectrometry (GC-MS) and direct microvial insert thermal desorption GC-MS. The most abundant volatile precursors in the genotypes were alcohols, followed by shikimic acid derivatives. High amounts of furanone glycosides were also detected, while norisoprenoids only existed in a small amount in blackberries. The volatile precursor composition in the genotypes in the 'Marion' pedigree was very similar to their free volatile distribution. 'Logan' and 'Olallie' predominantly had bound norisoprenoids. Wild 'Himalaya' predominated with terpene alcohol and furaneol glycosides, whereas 'Santiam' and 'Chehalem' contained a high level of terpene alcohol glycosides. A similar inheritance pattern was also observed for some volatile precursors in the genotypes in the 'Marion' pedigree. A high content of linalool, hydroxylinalool, and alpha-ionol glycosides in 'Olallie' and a low content in 'Chehalem' resulted in a moderate level in their offspring 'Marion', while a low content of (E)-linalool oxide precursor in 'Olallie' and a high content in 'Chehalem' also resulted in a moderate level in 'Marion'. However, the concentration of furaneol glycosides in 'Marion' exceeded that of its two parents.

Analysis of Organic Nitrogen Compounds in Urban Aerosol Samples Using GCxGC-TOF/MS

Despite the fact that a significant number of organic and inorganic compounds have been measured in aerosol samples, relatively little is known about the organic nitrogen (ON) content. The ON components of 23 urban aerosol samples were characterized using a direct thermal desorption technique (DTD) together with comprehensive two-dimensional gas chromatography-time of flight mass spectrometry (GCxGC-TOF/MS). Between 17 and 57 various ON compounds mainly nitriles, amides, amines, and nitro compounds were found in individual samples collected on different dates from the same location. In total identifications were made for over 100 ON different compounds in urban aerosol. Aminomethanesulfonic acid, o-cyanobenzoic acid and hexadecanenitrile were found in all samples. 4-[2-(methylamino)ethyl]-phenol, pyridine, 4,4a,5,7a-tetrahydro-8,8-dimethyl-(1à,4à, 4aà,7aà)-1,4-methano-1H-cyclopenta[d]pyridazine, caprolactam, tetradecanitrile, penoxaline, tetradecanamide, and eicosanenitrile were detected in many of the samples. ON compounds contained 1–4 N atoms and ranged in MW from 59–302 Da. DTD proved an efficient tool for the analysis of volatile organic nitrogen components in ambient aerosol, avoiding more costly and time consuming off-line extraction techniques. Desorption of ON standards on filter papers showed efficient transfer to the GC.

Analysis of Eucalyptus camaldulensis Volatiles from Turkey Using DTD-GC-MS

The direct analyses of the volatile organic components of 30 Eucalyptus camaldulensis fruit samples, obtained from the Antalya, Aegean and Cukurova regions in Turkey, was studied using a direct thermal desorption (DTD) technique coupled with gas chromatography mass spectrometry (GC-MS). It was found that the E. camaldulensis samples yielded a similar chemical composition. However, some of the compounds were only seen in one region, such as thymol in the Aegean region, ocimen and cis-sabinene hydrate in the Antalya region and nerolidol and pentacosane in the Cukurova region. A total of 68 components were identified from 30 samples. The main compounds found in the volatiles were: ledene (0–23.08 %), aromadendrene (0.59–42.31 %), alloaromadendrene (0–24.14 %), globulol (0–19.97 %) and isolongifolen (0–50.04 %). However, some of the quantities of the main compounds differed between samples. DTD with GC-MS is a good method for analysis of complex mixtures, and in particular for plant samples, which can yield data without the traditional obligation for costly and time consuming extraction techniques.

Analysis of the Volatile Organic Matter of Engine Piston Deposits by Direct Sample Introduction Thermal Desorption Gas Chromatography/Mass Spectrometry

This article establishes an alternative method for the characterization of volatiles organic matter (VOM) contained in deposits of the piston first ring grooves of diesel engines using a ChromatoProbe direct sample introduction (DSI) device coupled to gas chromatography/mass spectrometry (GC/MS) analysis. The addition of an organic solvent during thermal desorption leads to an efficient extraction and a good chromatographic separation of extracted products. The method was optimized investigating the effects of several solvents, the volume added to the solid sample, and temperature programming of the ChromatoProbe DSI device. The best results for thermal desorption were found using toluene as an extraction solvent and heating the programmable temperature injector from room temperature to 300 degrees C with a temperature step of 105 degrees C. With the use of the optimized thermal desorption conditions, several components have been positively identified in the volatile fraction of the deposits: aromatics, antioxidants, and antioxidant degradation products. Moreover, this work highlighted the presence of diesel fuel in the VOM of the piston deposits and gave new facts on the absence of the role of diesel fuel in the deposit formation process. Most importantly, it opens the possibility of quickly performing the analysis of deposits with small amounts of samples while having a good separation of the volatiles.

Specificity of the signal emitted by figs to attract their pollinating wasps: Comparison of volatile organic compounds emitted by receptive syconia of Ficus sur and F. sycomorus in Southern Africa

Volatile organic compounds (VOCs) appear to be critical for mediating the extreme specificity of the obligatory mutualisms between Ficus species (Moraceae) and their pollinating wasps (Hymenoptera, Chalcidoidea, Agaonidae). In the present study, we characterized the blend of VOCs emitted by receptive syconia of two closely related fig species F. sur and F. sycomorus. Headspace samples were collected, respectively, at three and four localities per species in South Africa and Swaziland, including one locality where both species were present, and were analyzed by gas chromatography–mass spectrometry (GC–MS) using a sensitive direct thermal desorption method. A total of 56 compounds were detected, most of which were terpenoids. Some of the major VOCs emitted by receptive figs are shared by both species. However, the relative proportions of these compounds in the total blend are different between F. sur and F. sycomorus. Multivariate analysis revealed a significant difference between the volatile profiles of the two species. These results support the hypothesis that the chemical messages emitted by figs are species-specific.

A New Method for Determining the Initial Mobile Formaldehyde Concentrations, Partition Coefficients, and Diffusion Coefficients of Dry Building Materials

The initial mobile formaldehyde concentration, C m,o; the partition coefficient, K; and the diffusion coefficient, D, of a dry building material are key parameters to characterize formaldehyde emissions from the building material. The solvent extraction method and direct thermal desorption method can overestimate C m,o because of high temperature. A new method has been developed to determine C m,o under similar conditions to common indoor environment, together with K and D. In the proposed method, the tested materials are placed in an airtight environmental chamber for which the temperature can be controlled by a water bath, then the materials undergo a multisorption/emission process and the instantaneous formalde-hyde concentration in the chamber is recorded. The K and C m,o are determined from the equilibrium concentrations after every sorption by means of the linear least-square regression, and D is obtained by fitting the concentration at the emission stage into a mass-transfer-based model in the literature. Four kinds of wooden medium-density boards are tested. The C m,o measured using this method is the mobile formaldehyde concentration in the material, which differs significantly from the total formaldehyde concentration in the material measured by using the traditional method recommended by the Chinese standard (GB/T 17657-1999) extraction method. This means that the mobile formaldehyde takes only a small portion of the total quantity in the tested material. The K, D, and C m,o values measured using this new method are used to predict formaldehyde concentrations for sorption processes. The results agree well with experimental data. In addition, some factors influencing the accuracy are analyzed.

Chemically modified porous silicon for laser desorption/ionization mass spectrometry of ionic dyes

Desorption/ionization on silicon (DIOS) mass spectra of model ionic dyes methylene blue (MB+Cl-) and methyl orange (Na+MO-) were studied using p+ type-derived porous silicon (PS) free layers. As-prepared PS (PS-H), the PS thermally oxidized at 300 degrees C (PS-OX), PS with chemically grafted cation-exchanging alkylsulfonic acid (PS-SO(3)H) and anion-exchanging propyl-octadecyldimethylammonium chloride (PS-ODMA+Cl-) groups was tested as ionization platforms. Two mechanisms of the methylene blue desorption/ionization were found: (1) the formation of [MB + H]+* ion due to the reduction/protonation of MB+, which is predominant for PS-H and PS-OX platforms and (2) direct thermal desorption of the MB+ cation, prevailing for PS-SO3H. The fragmentation of the cation is significantly suppressed in the latter case. The samples of PS-SO3H and PS-ODMA+ Cl- efficiently adsorb the dyes of the opposite charge from their solutions via the ion-exchange. Consequent DIOS MS studies allow to detect only low fragmented ions (MB+ and MO-, respectively), demonstrating the potential of the ion-exchange adsorption combined with DIOS MS for the analysis of ionic organic compounds in solutions.

Quantification of 2,5-dimethyl-4-hydroxy-3(2 H)-furanone using solid-phase extraction and direct microvial insert thermal desorption gas chromatography–mass spectrometry

A GC–MS method for the determination of furaneol in fruit juice was developed using Lichrolut-EN solid-phase extraction (SPE) coupled to microvial insert thermal desorption. Lichrolut-EN can effectively extract furaneol from juice, and had much less retention for pigments and other non-volatiles than HLB and C18 columns. The furaneol can be completely eluted out from the Lichrolut-EN SPE column with 1 mL of methanol, which can be directly analyzed on GC–MS using an automated large volume microvial insert thermal desorption technique without further purification and concentration. The method is sensitive, has good recovery (98%) and reproducibility (CV < 4%). The concentration of furaneol in some commonly grown strawberry, raspberry, and blackberry cultivars in Pacific Northwest of the United States was determined. Strawberries had the highest concentration of furaneol with ‘Totem’ and ‘Pinnacle’ cultivars over 13 mg kg −1 fruit. ‘Marion’ blackberry had 5 times more furaneol than ‘Black Diamond’, and 16 times more than ‘Thornless Evergreen’ blackberry. Raspberries had furaneol concentration ranged from 0.8 to 1.1 mg kg −1 fruit.

Determination of Volatile Chemical Constitutes in Tea by Simultaneous Distillation Extraction, Vacuum Hydrodistillation and Thermal Desorption

Generally the volatile compounds of tea are quite complicated and are found at trace levels (around 0.1% in total). The top-note of tea usually contains 40–100 main ingredients and is an analytical challenge to obtain qualitative and quantitative information of these volatile constitutes. The objective of this work is to apply the most suitable methods such as simultaneous distillation extraction, vacuum hydrodistillation extraction and direct thermal desorption to accurately determine the chemical components of a top-brand Chinese green tea and to compare the three volatile extraction methods. The analytical results are double confirmed by GC-sniffing, authentic raw materials and internal expert evaluation by reconstituting the top-note profile of the analyzed tea.

Thermal desorption characterisation of molecularly imprinted polymers. Part II: Use of direct probe GC–MS analysis to study crosslinking effects

A powerful method utilising direct probe thermal desorption GC-MS is presented for the study of molecularly imprinted polymers (MIPs). A series of 2-aminopyridine (2-apy)-imprinted methacrylic acid-ethyleneglycol dimethacrylate (MAA-EGDMA) copolymers were prepared under identical conditions but with varying amounts of EGDMA (crosslinking monomer). The use of appropriate temperature programmes permitted template removal, and the subsequent assessment of polymer affinity and specificity, all of which were found to be dependent on polymer composition and morphology. The system was sufficiently sensitive to identify a specific response of imprinted polymers over nonimprinted counterparts. Correlations were found to exist between thermal desorption analysis and solution phase binding, which was assessed by UV spectroscopy, where specificity was found to diminish with decreasing EGDMA concentration. This was attributed to the increased number of free carboxyl groups in those polymers containing a lower percentage of EGDMA. Thermal desorption profiles obtained for the analyte were found to be unaffected by the physical and chemical properties of the solvent used for analyte reloading.

Improved fatty acid detection in micro-algae and aquatic meiofauna species using a direct thermal desorption interface combined with comprehensive gas chromatography–time-of-flight mass spectrometry

Comprehensive two-dimensional gas chromatography (GC × GC) with time-of-flight mass spectrometry detection is used to profile the fatty acid composition of whole/intact aquatic microorganisms such as the common fresh water green algae Scenedesmus acutus and the filamentous cyanobacterium Limnothrix sp. strain MRI without any sample preparation steps. It is shown that the technique can be useful in the identification of lipid markers in food-web as well as environmental studies. For instance, new mono- and diunsaturated fatty acids were found in the C 16 and C 18 regions of the green algae S. acutus and the filamentous cyanobacterium Limnothrix sp. strain MRI samples. These fatty acids have not, to our knowledge, been detected in the conventional one-dimensional (1D) GC analysis of these species due to either co-elution and/or their presence in low amounts in the sample matrix. In GC × GC, all congeners of the fatty acids in these microorganisms could be detected and identified due to the increased analyte detectability and ordered structures in the two-dimensional separation space. The combination of direct thermal desorption (DTD)-GC × GC–time-of-flight mass spectrometry (ToF-MS) promises to be an excellent tool for a more accurate profiling of biological samples and can therefore be very useful in lipid biomarker research as well as food-web and ecological studies.

Composition of Eucalyptus camaldulensis Volatiles Using Direct Thermal Desorption Coupled with Comprehensive Two-Dimensional Gas Chromatography--Time-of-Flight-Mass Spectrometry

The direct qualification and quantitation of the volatile organic components of four Eucalyptus camaldulensis fruit samples, obtained from different geographical areas in Turkey, is studied using a direct thermal desorption (DTD) technique coupled with comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry. It is found that the E. camaldulensis sample from Adrasan gave a slightly higher oil yield (1.18%) than the others. The number of components quantitatively identified from Adrasan, Belek, Kuyucak, and Cesme were 46, 54, 55, and 59, respectively. The main compounds found in the volatile oils were: aromadendrene (6.45-15.02%), eucalyptol (0.17-12.61%), gamma-gurjunene (8.40-10.08%), terpinolen (1.98-8.39%), spathulenol (1.42-8.34%), alpha-pinene (0.85-6.81%), ledene (0.94-6.72%), and longifonene (0.07-6.22%). The composition of the volatiles desorbed from samples from all four different areas varied qualitatively and quantitatively. All identified compounds were quantitated using total ion chromatogram peak areas. DTD is a good method for qualitative and/or quantitative analysis of complex mixtures, and in particular for quantitative analysis of plant samples, which can yield data without the traditional obligation for costly and time consuming extraction techniques.

Chemical Composition of Volatile Oils from Leaves and Flowers of Sideritis congesta Using Direct Thermal Desorption - Two - Dimensional Gas Chromatography - Time - of - Flight Mass Spectrometry

Volatile oils from the leaves and flowers of Sideritis congesta, a plant endemic to Southern Anatolia, Turkey, were liberated using direct thermal desorption (DTD) and then analysed using comprehensive gas chromatography (GC × GC) coupled with time-of-flight mass spectrometry (TOF-MS). Two methods of thermal desorption are compared here; i) a manual direct cryo cooled on-column collection and focusing, and ii) a fully automated two stage carbon adsorbent thermal desorption system. 41 different volatile components were identified associated with plant leaves and 54 components for the flowers. A comparison of the flower volatiles resolved using the different thermal desorption methods indicated 43 common components, but with the cryo-cooled on-column method giving a slightly better determination. Major organic constituents observed from this species were Opinene (12.53–14.55 %), ß-pinene (17.15–25.34 %) and ô-cadinene (10.97–14.52 %). Results for manual and automated DTD methods are similar: both of them allow a fast plant volatile analysis without the costly and time consuming step of extraction or distillation.

Fatty acid profiling of raw human plasma and whole blood using direct thermal desorption combined with gas chromatography–mass spectrometry

Gas chromatography (GC) has in recent times become an important tool for the fatty acid profiling of human blood and plasma. An at-line procedure used in the fatty acid profiling of whole/intact aquatic micro-organisms without any sample preparation was adapted for this work. A direct thermal desorption (DTD) interface was used to profile the fatty acid composition of human plasma and whole human blood of eight volunteers in a procedure omitting the usual lipid extraction steps that precede sample methylation in the traditional (off-line) protocols. Trimethylsulfonium hydroxide (TMSH) was used as reagent for thermally assisted methylation. In a fully automated manner, the liner of the GC injector is used as a sample-and-reaction container with the aid of the DTD interface. The fatty acid methyl ester (FAME) profiles obtained using this novel approach, were very identical to those obtained when the traditional off-line protocol was applied. FAME yields obtained in the at-line DTD method were found to be very similar for saturated fatty acids, but significantly higher for polyunsaturated fatty acids compared to off-line yields. As a result of the contribution of circulating cell membranes in blood, substantial differences were observed when the amount of FAMEs obtained in whole human blood and human plasma samples were compared after their analysis. Thanks to the fully automated operation of this novel procedure, large series of analyses can easily be performed.

Determination of the carbon isotopic composition of whole/intact biological specimens using at-line direct thermal desorption to effect thermally assisted hydrolysis/methylation

In this paper, we discuss the use of a direct thermal desorption (DTD) interface as an alternative to Curie-point flash pyrolysis system as an inlet technique in gas chromatography–combustion isotope-ratio mass spectrometry (GC/C-IRMS) analysis of whole/intact phytoplankton and zooplankton specimens. The DTD in combination with a combipal auto-injector is programmed to perform the injection, evaporation of solvents, transport of capped programmed-temperature vaporizer (PTV) liners to the PTV injector and chemical derivatisation (thermally assisted hydrolysis/methylation; THM) such that a profile of a cellular fatty acids is obtained. Flow-cytometric sorted microalgae and handpicked zooplankton are used as samples with trimethylsulfonium hydroxide (TMSH) as methylating reagent. A major advantage of this novel approach over the Curie-point technique is the automation of the total procedure, which allows unattended analysis of large sample series. The profiles and δ 13C carbon isotopic signatures of the fatty acid methyl esters (FAMEs) produced are very similar to those obtained using the Curie-point flash pyrolysis method. It is shown that algal samples must be kept no longer than 48 h in the DTD sample tray prior to the THM-analysis in order to maintain the integrity of their FAME profile.

Decontamination of soil containing POPs by the combined action of solid Fenton-like reagents and microwaves

The effect on halogenated aromatics of solid, non-toxic oxidants such as sodium percarbonate and the urea/hydrogen peroxide complex (Fenton-like reagents) was investigated. A microwaves-assisted, solvent-free method for soil decontamination is presented. It marks a considerable advance in the search of more efficient, environment-friendly procedures for the degradative oxidation of persistent organic pollutants. Residual pollutants in treated soil samples were determined by GC/MS analysis after solvent extraction or direct thermal desorption. Results showed that 4-chloronaphthol, 2,4-dichlorophenoxyacetic acid and p-nonylphenol had been degraded completely, 2,4-dibromophenol to a large extent.

Characterization of olive oil volatiles by multi-step direct thermal desorption–comprehensive gas chromatography–time-of-flight mass spectrometry using a programmed temperature vaporizing injector

The feasibility of a versatile system for multi-step direct thermal desorption (DTD) coupled to comprehensive gas chromatography (GC × GC) with time-of-flight mass spectrometric (TOF-MS) detection is studied. As an application the system is used for the characterization of fresh versus aged olive oil after treatment at 70, 175, 250 and 600 °C.