Article

Capturing in Vivo Plant Metabolism by Real-Time Analysis of Low to High Molecular Weight Volatiles

Authors:
  • Fossil Ion Technology S.L., Madrid, Spain
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Abstract

We have deployed an efficient secondary electrospray ionization source coupled to an Orbitrap mass analyzer (SESI-MS) to investigate the emissions of a Begonia Semperflorens. We document how hundreds of species can be tracked with an unparalleled time resolution of 2 min during day-night cycles. To further illustrate the capabilities of this system for volatile organic compounds (VOCs) analysis, we subjected the plant to mechanical damage and monitored its response. As a result, ~ 1,200 of VOCs were monitored displaying different kinetics. To validate the soundness of our in vivo measurements, we fully characterized some key compounds via MS/MS and confirmed their expected behavior based on prior gas chromatography-mass spectrometry (GC-MS) studies. For example, β-caryophyllene, which is directly related to photosynthesis, was found to show a periodic day-night pattern with highest concentrations during the day. We conclude that the capability of SESI-MS to capture highly dynamic VOC emissions and wide analyte coverage makes it an attractive tool to complement GC-MS in plant studies.

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Data
February 2016
César Barrios-Collado · Diego García-Gómez · Renato Zenobi · Guillermo Vidal · Pablo Sinues
Data
February 2016
César Barrios-Collado · Diego García-Gómez · Renato Zenobi · Guillermo Vidal · Pablo Sinues
... Desorption Solvent back-extraction [40,53], Heat desorption [34], Heat desorption (thermal desorption unit-TDS) [31,47] Heat desorption [37] Heat desorption [97 Heat desorption [81] Heat desorption (TDS) [15,89] Analytical platform GC-MS [43], ESI a -MS [49], GC-FID [71], GC-DMS b [39], PTR-MS [47], CO laser-based detector [28] GC-MS [37], GC-FID [37], PTR-MS [37], GC Â GC-MS [58] GC-MS [72], GC-ICPMS c [64], GC-ITMS d [97], GC-IMS e [96], GC Â GC-MS [104] GC-MS [82], GC Â GC-MS [5] GC-MS [15,89] Topographical analysis stationary phase is unable to re-concentrate the most volatile BVOCs in a narrow band at the head of the column, thus generating highly broadened peaks. The desorption band is generally reconcentrated at very low temperatures either by a PTV injector or by using a cryogenically cooled oven or by special cryosystems coated around the first coil(s) of the column. ...
... Direct infusion high-resolution mass spectrometer (HRMS) with a secondary electrospray ionization source (SESI-Orbitrap-MS) was also applied by Barrios-Collado et al. for the real-time monitoring of BVOCs [49]. The direct MS approach resulted very effective and informative for the determination of more than 1200 BVOCs emitted by Begonia semperflorens Link & Otto; the results were validated by both characterizing some key components via tandem mass spectrometry (MS/MS) with the above HRMS system, and by comparing the results to those obtained by GC-MS [49]. ...
... Direct infusion high-resolution mass spectrometer (HRMS) with a secondary electrospray ionization source (SESI-Orbitrap-MS) was also applied by Barrios-Collado et al. for the real-time monitoring of BVOCs [49]. The direct MS approach resulted very effective and informative for the determination of more than 1200 BVOCs emitted by Begonia semperflorens Link & Otto; the results were validated by both characterizing some key components via tandem mass spectrometry (MS/MS) with the above HRMS system, and by comparing the results to those obtained by GC-MS [49]. ...
Article
Biogenic volatile organic compounds (BVOCs) are metabolites emitted by living plants that have a fundamental ecological role since they influence atmospheric chemistry, plant communication and pollinator/herbivore behaviour, and human activities. Over the years, several strategies have been developed to isolate and identify them, and to take advantage of their activity. The main techniques used for in-vivo analyses include dynamic headspace (D-HS), static headspace (S-HS) and, more recently, direct contact (DC) methods in association with gas chromatography (GC) and mass spectrometry (MS). The aim of this review is to provide insight into the in-vivo characterisation of plant volatile emissions with a focus on sampling, analysis and possible applications. This review first provides a critical discussion of the challenges associated with conventional approaches and their limitations and advantages. Then, it describes a series of applications of in-vivo volatilomic studies to enhance how the information they provide impact on our knowledge of plant behaviour, including the effects of abiotic (damage, flooding, climate) and biotic (insect feeding) stress factors in relation to the plants.
... Excitingly, VOCs are produced by all kinds of organisms including microorganisms (Sinha et al. 2017;Lemfack et al. 2017;Huang and Hull 2017), plants (Pattrick et al. 2017;Barrios-Collado et al. 2016;Clavijo McCormick et al. 2014), insects (Wicher 2015;Gomez-Diaz and Benton 2013), and 1 3 mammals (Kücklich et al. 2017;Filipiak et al. 2016;Rattray et al. 2014). The entirety of the VOCs produced by an organism has been termed the volatilome (or volatome) (Filipiak et al. 2016;Amann et al. 2014;Heddergott et al. 2014;Das et al. 2014;Phillips et al. 2013). ...
... Ideally, one is able to directly quantify all volatiles that collectively define the phenotype. Hence, MS-based analyses can be subdivided in two approaches: (a) online, also known as real time (Singh et al. 2017;Tejero Rioseras et al. 2017;Barrios-Collado et al. 2016;Blake et al. 2009) and offline or chromatography based (Das et al. 2014;Phillips et al. 2013;Rubiolo et al. 2008;Bicchi et al. 2000;Pauling et al. 1971). ...
... In the particular case of the latter, major advantages of SESI source compared to the previous two are: its high ionization efficiency (similar to Chemical Ionization) and its flexibility, since it can be interfaced with different commercial mass spectrometers. Hence, the VOCs that are "sniffed" by a SESI source can be monitored by high-resolution tandem MS instruments, which allows for the detection of thousands of chemical entities in a single sample (Tejero Rioseras et al. 2017;Barrios-Collado et al. 2016). This simplicity is barely appreciable in smallscale studies with tens of samples, but becomes absolutely critical in mid-scale-to-large-scale studies with hundreds or thousands of samples. ...
Article
Volatile organic compounds (VOCs) are small molecular mass substances, which exhibit low boiling points and high-vapour pressures. They are ubiquitous in nature and produced by almost any organism of all kingdoms of life. VOCs are involved in many inter- and intraspecies interactions ranging from antimicrobial or fungal effects to plant growth promotion and human taste perception of fermentation products. VOC profiles further reflect the metabolic or phenotypic state of the living organism that produces them. Hence, they can be exploited for non-invasive medicinal diagnoses or industrial fermentation control. Here, we introduce the reader to these diverse applications associated with the monitoring and analysis of VOC emissions. We also present our vision of real-time VOC analysis enabled by newly developed analytical techniques, which will further broaden the use of VOCs in even wider applications. Hence, we foresee a bright future for VOC research and its associated fields of applications.
... An alternative approach is to encompass the entire plant and direct the flow of ambient gas through the sampling chamber and into the DI-MS instrument. The enclosures can range from glass jars [55], beakers [56], and polymer containers [50] to sophisticated systems that enable a comprehensive analysis of volatile plant metabolites [57,58]. ...
... The current trend is to integrate DI-MS with 'omics platforms through coupling with other highthroughput techniques, which will allow for comprehensive use of metabolomics, genomics, proteomics, and so on [81][82][83], and will provide unprecedented insights into the complex processes occurring at each stage of plant development. Furthermore, despite the clear advantages of using PTR-MS for the analysis of plant volatiles, researchers are already investigating alternative ionization sources compatible with high-resolution mass spectrometers, potentially enabling sub-ppt sensitivity [35,56]. Such developments in instrumentation might spur the more widespread use of DI-MS in applications, in which the analytes are at trace concentration levels, such as in the monitoring of BVOC flux in the atmosphere of entire ecosystems. ...
Article
The use of the 'omics techniques in environmental research has become common-place. The most widely implemented of these include metabolomics, proteomics, genomics, and transcriptomics. In recent years, a similar approach has also been taken with the analysis of volatiles from biological samples, giving rise to the so-called 'volatilomics' in plant analysis. Developments in direct infusion mass spectrometry (DI-MS) techniques have made it possible to monitor the changes in the composition of volatile flux from parts of plants, single specimens, and entire ecosystems in real-time. The application of these techniques enables a unique insight into the dynamic metabolic processes that occur in plants. Here, we provide an overview of the use of DI-MS in real-time volatilomics research involving plants.
... These high-throughput methods also benefit from the parallel determination of many analytes or reaction intermediates in a single analytical cycle/assay. Gas-phase samples (breath analysis, industrial effluents, and so on) can be also easily monitored in real time using Ambient MS [38]. ...
Article
A recent subdiscipline of mass spectrometry that has undergone a relentless growth is Ambient Mass Spectrometry (Ambient MS). This realm, coined first by R. Graham Cooks (Science, 2004, 306, 1571-1573) refers to the ability of interrogating samples in their native state (solid, liquid or gas) using atmospheric-pressure sampling mass spectrometry with minimal or even no sample preparation. In this experiment, sample and analyte ionization takes place at ambient conditions together with the desorption of the species from the studied sample, if applies; ions are thus generated outside the MS instrument and subsequently mass analyzed. This feature map well against the Green Analytical Chemistry (GAC) principles particularly when Ambient MS is implemented in low-power consumption portable mass spectrometry instrumentation. This article provides a glimpse of Ambient MS from the GAC perspective, including illustrative examples on recent applications of societal impact including clinical diagnosis, food safety, environmental monitoring, forensics or homeland security.
... This study showed a correlation of 400 compounds with light levels (diurnal and nocturnal), some of which were further identified by MS/MS. These findings show the usefulness of SESI-MS to provide complementary real-time chemical information on the plant metabolome (Barrios-Collado et al., 2016). ...
Chapter
Plant metabolism is profoundly involved in physiological regulation and defence responses when the environment is adverse and plant growth and development is negatively affected. Metabolomics techniques allow the characterisation of physiological and biochemical responses to different types of environmental stresses in plants, including drought, salinity, and nutrient deficiencies. Metabolomics analyses of plant systems have been mostly carried out on bulked tissues (i.e. whole roots, leaves, or shoots) which can provide important biological information about plant tolerance and avoidance mechanisms to abiotic stresses. However, individual plant organs and tissues are composed of different kinds of cells which can produce specific metabolic responses to abiotic stress. Thus, recent development and improvement of metabolomics techniques have allowed the analysis of plant metabolic changes in a spatially resolved manner (i.e. in vivo metabolomics, cell-specific metabolomics, and mass spectrometry imaging (MSI)-based metabolomics). This article provides a comprehensive overview of the recent findings on plant metabolite changes in response to abiotic stress, recent advancements in metabolomics techniques to study plant metabolism, and prospects of MSI-based plant metabolomics for the study of plant metabolism.
... The ionized analytes are guided into the MS. A very impressive real-time analysis by SESI- MS reported the day-night cycle of about 400 volatile metabolites of the plant Begonia semperflorens [21]. ...
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Rational strain engineering requires solid testing of phenotypes including productivity and ideally contributes thereby directly to our understanding of the genotype-phenotype relationship. Actually, the test step of the strain engineering cycle becomes the limiting step, as ever advancing tools for generating genetic diversity exist. Here, we briefly define the challenge one faces in quantifiying phenotypes and summarize existing analytical techniques that partially overcome this challenge. We argue that the evolution of volatile metabolites can be used as proxy for cellular metabolism. In the simplest case, the product of interest is a volatile (e.g., from bulk alcohols to special fragrances) that is directly quantified over time. But also nonvolatile products (e.g., from bulk long-chain fatty acids to natural products) require major flux rerouting that result potentially in altered volatile production. While alternative techniques for volatile determination exist, rather few can be envisaged for medium to high-throughput analysis required for phenotype testing. Here, we contribute a detailed protocol for an ion mobility spectrometry (IMS) analysis that allows volatile metabolite quantification down to the ppb range. The sensivity can be exploited for small-scale fermentation monitoring. The insights shared might contribute to a more frequent use of IMS in biotechnology, while the experimented aspects are of general use for researchers interested in volatile monitoring.
... In line with such efforts to develop instrumentation capable of monitoring time-resolved metabolic information, we show here how secondary electrospray ionization (SESI) [27][28][29][30][31][32][33][34][35][36][37][38][39] coupled to high resolution mass spectrometry (HRMS) captures on-line an unprecedented wealth of volatile analytes emitted in vivo by growing baker's yeast (Saccharomyces cerevisiae). ...
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While yeast is one of the most studied organisms, its intricate biology remains to be fully mapped and understood. This is especially the case when it comes to capture rapid, in vivo fluctuations of metabolite levels. Secondary electrospray ionization-high resolution mass spectrometry SESI-HRMS is introduced here as a sensitive and noninvasive analytical technique for online monitoring of microbial metabolic activity. The power of this technique is exemplarily shown for baker’s yeast fermentation, for which the time-resolved abundance of about 300 metabolites is demonstrated. The results suggest that a large number of metabolites produced by yeast from glucose neither are reported in the literature nor are their biochemical origins deciphered. With the technique demonstrated here, researchers interested in distant disciplines such as yeast physiology and food quality will gain new insights into the biochemical capability of this simple eukaryote.
... Electrospray plumes not only ionize solvated analytes, but also are capable of ionizing gas-phase species (Whitehouse et al., 1986;Chen et al., 1994), the latter termed secondary electrospray ionization (SESI;Wu et al., 2000;Tam and Hill, 2004). SESI-MS has been used for the real-time analysis of a variety of gas-phase analytes, including pharma-ceuticals (Wu et al., 2000;Meier et al., 2012), explosives (Tam and Hill et al., 2004;Aernecke et al., 2015), human metabolites (Martinez-Lozano et al., 2011;Garcia-Gomez et al., 2015), electronic cigarette vapors (), volatile emissions from bacteria cultures (Zhu et al., 2010), food (Bean et al., 2015;Farrell et al., 2017), and plants (Barrios-Collado et al., 2016). In SESI, the electrospray plume and incoming sample flow intersect in the ionization region, and analyte ionization proceeds likely via interactions with both small charged droplets and electrosprayproduced gas-phase reagent ions (Wu et al., 2000). ...
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We present an electrospray ion source coupled to an orthogonal continuous-flow atmospheric pressure chemical ionization region. The source can generate intense and stable currents of several specific reagent ions using a range of salt solutions prepared in methanol, thereby providing both an alternative to more common radioactive ion sources and allowing for the generation of reagent ions that are not available in current chemical ionization mass spectrometry (CIMS) techniques, such as alkaline cations. We couple the orthogonal electrospray chemical ionization (ESCI) source to a high-resolution time-of-flight mass spectrometer (HR-ToF-MS), and assess instrument performance through calibrations using nitric acid (HNO3), formic acid (HCOOH), and isoprene epoxydiol (trans-β-IEPOX) gas standards, and through measurements of oxidized organic compounds formed from ozonolysis of α-pinene in a continuous-flow reaction chamber. When using iodide as the reagent ion, the HR-ToF-ESCIMS prototype has a sensitivity of 11, 2.4, and 10 cps pptv⁻¹ per million counts per second (cps) of reagent ions and a detection limit (3σ, 5 s averaging) of 4.9, 12.5, and 1.4 pptv to HNO3, HCOOH, and IEPOX, respectively. These values are comparable to those obtained using an iodide-adduct HR-ToF-CIMS with a radioactive ion source and low-pressure ion–molecule reaction region. Applications to the α-pinene ozonolysis system demonstrates that HR-ToF-ESCIMS can generate multiple reagent ions (e.g., I⁻, NO3⁻, acetate, Li⁺, Na⁺, K⁺, and NH4⁺) having different selectivity to provide a comprehensive molecular description of a complex organic system.
... Barrios e Collado et al. developed a real-time in vivo detection system for flower volatiles. They deployed secondary electrospray ionization source coupled to an Orbitrap mass analyzer (SESI-MS) to investigate the emission of a Begonia semperflorens without the preconcentration process of analytes using SPME [42]. They enclosed the flower pot within a 5 L glass beaker. ...
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The dynamics of plant volatile (PV) emission, and the relationship between damaged area and biosynthesis of bioactive molecules in plant-insect interactions, remain open questions. Direct Contact-Sorptive Tape Extraction (DC-STE) is a sorption sampling technique employing non adhesive polydimethylsiloxane tapes, which are placed in direct contact with a biologically-active surface. DC-STE coupled to Gas Chromatography - Mass Spectrometry (GC-MS) is a non-destructive, high concentration-capacity sampling technique able to detect and allow identification of PVs involved in plant responses to biotic and abiotic stresses. Here we investigated the leaf topographical dynamics of herbivory-induced PV (HIPV) produced by Phaseolus lunatus L. (lima bean) in response to herbivory by larvae of the Mediterranean climbing cutworm (Spodoptera littoralis Boisd.) and mechanical wounding by DC-STE-GC-MS. Time-course experiments on herbivory wounding caused by larvae (HW), mechanical damage by a pattern wheel (MD), and MD combined with the larvae oral secretions (OS) showed that green leaf volatiles (GLVs) [(E)-2-hexenal, (Z)-3-hexen-1-ol, 1-octen-3-ol, (Z)-3-hexenyl acetate, (Z)-3-hexenyl butyrate] were associated with both MD and HW, whereas monoterpenoids [(E)-β-ocimene], sesquiterpenoids [(E)-nerolidol] and homoterpenes (DMNT and TMTT) were specifically associated with HW. Up-regulation of genes coding for HIPV-related enzymes (Farnesyl Pyrophosphate Synthase, Lipoxygenase, Ocimene Synthase and Terpene Synthase 2) was consistent with HIPV results. GLVs and sesquiterpenoids were produced locally and found to influence their own gene expression in distant tissues, whereas (E)-β-ocimene, TMTT, and DMNT gene expression was limited to wounded areas. DC-STE-GC-MS was found to be a reliable method for the topographical evaluation of plant responses to biotic and abiotic stresses, by revealing the differential distribution of different classes of HIPVs. The main advantages of this technique include: a) in vivo sampling; b) reproducible sampling; c) ease of execution; d) simultaneous assays of different leaf portions, and e) preservation of plant material for further "omic" studies. DC-STE-GC-MS is also a low-impact innovative method for in situ PV detection that finds potential applications in sustainable crop management.
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A two-stage thermal desorption/secondary electrospray ionization/time-of-flight mass spectrometry for faster targeted breath profiling has been studied. A new secondary electrospray ionization (SESI) source was devised to constrain the thermal desorption plume and promote efficient mixing in the ionization region. Further, a chromatographic pre-separation stage was introduced to suppress interferences from siloxanes associated with thermal desorption profiles of exhaled breath samples. In vitro tests with 5-nonanone indicated an increased sensitivity and a lowered limit-of-detection, both by a factor of ~4, the latter to an on-trap mass of 14.3 ng, equivalent to a sampled breath concentration of 967 pptv. Analysis of the mass spectrometric responses from 20 breath samples acquired sequentially from a single participant indicated enhanced reproducibility (reduced relative standard deviations (RSD) for 5-nonanone, benzaldehyde and 2-butanone were 28 %, 16% and 14% respectively. The corresponding values for an open SESI source were that 5-nonanone was not detected, with %RSD of 39% for benzaldehyde and 31% for 2-butanone). The constrained source with chromatographic pre-separation resulted in an increase in the number of detectable volatile organic compounds (VOCs) from 260 mass spectral peaks with an open SESI source to 541 peaks with the constrained source with pre-separation. Most of the observed VOCs were present at trace levels, at less than 2.5% of the intensity of the base peak. Seventeen 2.5 dm³ distal breath samples were collected from asthma patients and healthy controls respectively, and subjected to comparative high-throughput screening using thermal desorption/SESI/time-of-flight mass spectrometry (TD-SESI-ToFMS). Breath metabolites were detected by using a background siloxane ion (hexamethylcyclotrisiloxane m/z 223.0642) as an internal lockmass. Eleven breath metabolites were selected from the breath research literature and successfully targeted. These data reinforce the proposition that TD-SESI-MS has potential for development as a rapid screening method for disease stratification and targeted metabolism profiling.
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There is increasing interest in the development of noninvasive diagnostic methods for early cancer detection, to improve the survival rate and quality of life of cancer patients. Identification of volatile metabolic compounds may provide an approach for noninvasive early diagnosis of malignant diseases. Here we analyzed the volatile metabolic signature of human breast cancer cell lines versus normal human mammary cells. Volatile compounds in the headspace of conditioned culture medium were directly fingerprinted by secondary electrospray ionization-mass spectrometry. The mass spectra were subsequently treated statistically to identify discriminating features between normal vs. cancerous cell types. We were able to classify different samples by using feature selection followed by principal component analysis (PCA). Additionally, high-resolution mass spectrometry allowed us to propose their chemical structures for some of the most discriminating molecules. We conclude that cancerous cells can release a characteristic odor whose constituents may be used as disease markers.
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Background and AimsFloral traits, such as floral volatiles, can contribute to pre-zygotic reproductive isolation by promoting species-specific pollinator foraging. When hybrid zones form, floral traits could also influence post-zygotic isolation. This study examined floral volatiles in parental species and natural hybrids in order to explore potential scent mediation of pre-zygotic and post-zygotic isolation.Methods Floral bouquets were analysed for the sister species Ipomopsis aggregata and I. tenuituba and their natural hybrids at two contact sites differing in both hybridization rate and temporal foraging pattern of hawkmoth pollinators. Floral volatiles were quantified in diurnal and nocturnal scent samples using gas chromatography-mass spectrometry.Key ResultsThe bouquets of parental species and hybrids showed qualitative overlap. All flowers emitted similar sets of monoterpenoid, sesquiterpenoid, aliphatic and benzenoid compounds, but separated into groups defined by multivariate analysis of quantitative emissions. The parental species differed most strikingly in the nitrogenous compound indole, which was found almost exclusively in nocturnal bouquets of I. tenuituba. Natural hybrid bouquets were highly variable, and showed emission rates of several compounds that appeared transgressive. However, indole emission rates were intermediate in the hybrids compared with rates in the parents. Volatile bouquets at the contact site with lower hybridization did not show greater species specificity in overall scent emission, but I. tenuituba presented a stronger indole signal during peak hawkmoth activity at that site.Conclusions The two species of Ipomopsis differed in patterns of floral bouquets, with indole emitted in nocturnal I. tenuituba, but not in I. aggregata. Natural hybrid bouquets were not consistently intermediate between the parents, although hybrids were intermediate in indole emission. The indole signal could potentially serve as a hawkmoth attractant that mediates reproductive isolation both before and after hybrid formation.
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A meshless continuum formulation is presented. The formulation resembles the element free Galerkin method, where discrete nodes (or particles) are mutually attached via shape functions constructed from moving least squares approximations. No reference to any type of mesh is made. The performance of the present formulation is superior to the performance of other methods in problems involving strain localization, fracture, contact, or extreme deformations. This paper documents the construction of discrete equations as well as continuum-mechanical details concerning the behavior of ductile as well as brittle solids. In the meshless analysis both Eulerian and Lagrangian shape functions can be applied. Eulerian shape functions are calculated from the nodes' spatial coordinates and are constantly updated. In contrast, the Lagrangian shape functions are calculated from the nodes' convected material coordinates. The Lagrangian shape functions provide the most stable simulations, whereas Eulerian shape functions lead to numerical instabilities. It is demonstrated how the meshless formulation provides an objective framework for studying crustal strain localizations as the meshless method does not suffer from the mesh sensitivity of the finite element method. In addition, examples on applications in fracture and contact problems are given through ductile necking and folding.
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Trace gas monitoring plays an important role in many areas of life sciences ranging from agrotechnology, microbiology, molecular biology, physiology, and phytopathology. In plants, many processes can be followed by their low-concentration gas emission, for compounds such as ethylene, nitric oxide, ethanol or other volatile organic compounds (VOCs). For this, numerous gas-sensing devices are currently available based on various methods. Among them are the online trace gas detection methods; these have attracted much interest in recent years. Laser-based infrared spectroscopy and proton transfer reaction mass spectrometry are the two most widely used methods, thanks to their high sensitivity at the single part per billion level and their response time of seconds. This paper starts with a short description of each method and presents performances within a wide variety of biological applications. Using these methods, the dynamics of trace gases for ethylene, nitric oxide and other VOCs released by plants under different conditions are recorded and analysed under natural conditions. In this way many hypotheses can be tested, revealing the role of the key elements in signalling and action mechanisms in plants.
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This article describes a new photoacoustic FT-IR system capable of operating at elevated temperatures. The key hardware component is an optical-readout cantilever microphone that can work up to 200 °C. All parts in contact with the sample gas were put into a heated oven, incl. the photoacoustic cell. The sensitivity of the built photoacoustic system was tested by measuring 18 different VOCs. At 100 ppm gas concentration, the univariate signal to noise ratios (1σ, measurement time 25.5 min, at highest peak, optical resolution 8 cm(-1)) of the spectra varied from minimally 19 for o-xylene up to 329 for butyl acetate. The sensitivity can be improved by multivariate analyses over broad wavelength ranges, which effectively co-adds the univariate sensitivities achievable at individual wavelengths. The multivariate limit of detection (3σ, 8.5 min, full useful wavelength range), i.e., the best possible inverse analytical sensitivity achievable at optimum calibration, was calculated using the SBC method and varied from 2.60 ppm for dichloromethane to 0.33 ppm for butyl acetate. Depending on the shape of the spectra, which often only contain a few sharp peaks, the multivariate analysis improved the analytical sensitivity by 2.2 to 9.2 times compared to the univariate case. Selectivity and multi component ability were tested by a SBC calibration including 5 VOCs and water. The average cross selectivities turned out to be less than 2% and the resulting inverse analytical sensitivities of the 5 interfering VOCs was increased by maximum factor of 2.2 compared to the single component sensitivities. Water subtraction using SBC gave the true analyte concentration with a variation coefficient of 3%, although the sample spectra (methyl ethyl ketone, 200 ppm) contained water from 1,400 to 100k ppm and for subtraction only one water spectra (10k ppm) was used. The developed device shows significant improvement to the current state-of-the-art measurement methods used in industrial VOC measurements.
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Proton transfer reaction-time of flight (PTR-TOF) mass spectrometry was used to improve detection of biogenic volatiles organic compounds (BVOCs) induced by leaf wounding and darkening. PTR-TOF measurements unambiguously captured the kinetic of the large emissions of green leaf volatiles (GLVs) and acetaldehyde after wounding and darkening. GLVs emission correlated with the extent of wounding, thus confirming to be an excellent indicator of mechanical damage. Transient emissions of methanol, C5 compounds and isoprene from plant species that do not emit isoprene constitutively were also detected after wounding. In the strong isoprene-emitter Populus alba, light-dependent isoprene emission was sustained and even enhanced for hours after photosynthesis inhibition due to leaf cutting. Thus isoprene emission can uncouple from photosynthesis and may occur even after cutting leaves or branches, e.g., by agricultural practices or because of abiotic and biotic stresses. This observation may have important implications for assessments of isoprene sources and budget in the atmosphere, and consequences for tropospheric chemistry.
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Isoprene emission represents a significant loss of carbon to those plant species that synthesize this highly volatile and reactive compound. As a tool for studying the role of isoprene in plant physiology and biochemistry, we developed transgenic tobacco plants capable of emitting isoprene in a similar manner to and at rates comparable to a naturally emitting species. Thermotolerance of photosynthesis against transient high-temperature episodes could only be observed in lines emitting high levels of isoprene; the effect was very mild and could only be identified over repetitive stress events. However, isoprene-emitting plants were highly resistant to ozone-induced oxidative damage compared with their non-emitting azygous controls. In ozone-treated plants, accumulation of toxic reactive oxygen species (ROS) was inhibited, and antioxidant levels were higher. Isoprene-emitting plants showed remarkably decreased foliar damage and higher rates of photosynthesis compared to non-emitting plants immediately following oxidative stress events. An inhibition of hydrogen peroxide accumulation in isoprene-emitting plants may stall the programmed cell death response which would otherwise lead to foliar necrosis. These results demonstrate that endogenously produced isoprene provides protection from oxidative damage.
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Leaves normally release small quantities of volatile chemicals, but when a plant is damaged by herbivorous insects, many more volatiles are released. The chemical identity of the volatile compounds varies with the plant species and with the herbivorous insect species. These volatiles attract both parasitic and predatory insects that are natural enemies of the herbivores. They may also in- duce defense responses in neighboring plants. Such chem- icals, which function in communication between and among species, as well as those that serve as messengers between members of the same species, are called semio- chemicals (from the Greek "semeion," a mark or signal) (Law and Regnier, 1971). Semiochemicals emitted from a diverse group of plants and insects mediate key processes in the behavior of spe- cific insects. Volatile phytochemicals can serve as airborne semiochemicals, promoting or deterring interactions be- tween plants and insect herbivores. For example, wheat seedlings without herbivore damage attract aphids, whereas odors released from wheat seedlings with a high density of aphids repel other aphids (Quiroz et al., 1997). For swallowtail butterflies, volatiles from host plants enhance the effect of contact stimulants, increasing landing rates and oviposition relative to non-host plants (Feeny et al., 1989). In addition to the bouquet of compounds that render leaves attractive or disagreeable to herbivores, volatile ter- penoids and other compounds emitted from leaves in re-
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The identification of chemical compounds in exhaled human breath is promising in the search for new biomakers of diseases. However, the analytical techniques used nowadays are not capable of achieving a robust identification, especially in real-time analysis. In this work, we show that real-time high-resolution tandem mass spectrometry (HRMS/MS) suitable for the identification of biomarkers in exhaled breath. Using this approach, we identified a number of furan derivatives, compounds found in the exhalome whose nature and origin are not yet clearly understood. It is also shown that the combination of HRMS/MS with UHPLC allowed not only the identification of the furan derivatives but also the proper separation of their isomeric forms.
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A number of direct injection mass spectrometry methods that can sample foods non-destructively and without sample preparation are being developed, with applications ranging from the rapid assessment of food safety to the verification of protected designations of origin. In this pilot study we used secondary electrospray ionization-mass spectrometry (SESI-MS) in positive- and negative-ion modes to collect the volatile fingerprints of artisanal Cheddar cheeses aged for one to three years. We found that the SESI-MS fingerprints change in an aging-dependent manner, and that we can descriptively and predictively categorize Cheddars by their aging period, identify volatile components that increase or decrease with aging, and robustly discriminate individual batches of artisanal cheese. From these results we conclude that SESI-MS volatile fingerprinting could be used by artisanal food producers to characterize their products during production and aging, providing useful data that helps them maximize the value of each batch.
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In recent years, breath analysis in real time has become a non-invasive alternative for the diagnosis of diseases and for molecular fingerprinting of exhaled breath. However, the techniques used lack the capabilities for proper identification of the compounds found in the exhalome. Here, we report the use of UHPLC-HRMS as a tool for the identification of several aldehydes (2-alkenals, 4-hydroxy-2-alkenals and 4-hydroxy-2,6-alkadienals), biomarkers of lipid peroxidation, in exhaled breath condensate of three healthy subjects (N=3). Some of the aldehydes studied have never been identified before. Their robust identification is based on retention times, on the generation of fragmentation trees from tandem mass spectra, and on the comparison of these parameters with standards. We also show that the identified compounds can be analyzed and confirmed by MS/MS in breath in real time and, therefore, they could be used as biomarkers for the rapid and non-invasive diagnosis of related diseases.
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Blood cultures are routine tests to determine whether micro-organisms have entered the patient's bloodstream. Automated systems, based on the detection of CO2 increase in the culture media, have considerably improved the screening efficiency for the detection of bacteria.1 However, further identification of bacteria still requires time-consuming culturing procedures. It has been suggested that along with CO2, bacterial cultures emit characteristic volatile organic compounds that may be valuable for characterisation.2 Recently, a number of technological developments have allowed the detection of trace gases with minimal or no sample preconcentration steps.3–5 In the current study, we investigated whether the volatiles emitted from bacterial cultures (mimicking routine clinical blood cultures) could be distinguished from each other in a rapid fashion by secondary electrospray ionisation-mass spectrometry (SESI-MS).6 ,7 103 colony forming units were inoculated in 42 aerobic bottles: 15 with Staphylococcus aureus ATCC 29213 strain, 15 with Escherichia coli ATCC 25922 and 12 Streptococcus pneumoniae ATCC 49619. They were incubated in the automatic instrument BacT/ALERT 3D (Biomerieux Clinical Diagnostic, France). The system automatically detects the positivity of the sample when the amount of CO2 produced by bacterial growth reaches a given threshold. …
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Breath is considered to be an easily accessible matrix, whose chemical composition relates to compounds present in blood. Therefore many metabolites are expected in exhaled breath, which may be used in the future for the development of diagnostic methods. In this article, a new strategy to discriminate between exhaled endogenous metabolites and exhaled exogenous contaminants by direct high-resolution mass spectrometry is introduced. The analysis of breath in real-time by secondary electrospray ionization mass spectrometry allows to interpret the origin of exhaled compounds. Exhaled metabolites that originate in the respiratory system show reproducible and significant patterns if plotted in real-time (>1 data point per second). An exhaled metabolite shows a signal that tends to rise at the end of a complete (forced) exhalation. In contrast, exogenous compounds, which may be present in room air, are gradually diluted by the air from the deeper lung and therefore show a trend of falling intensity. Signals found in breath by using this pattern recognition are linked to potential metabolites by comparison with online databases. In addition to this real-time approach, it is also shown how to combine this method with classical analytical methods in order to potentially identify unknown metabolites. Finally exhaled compounds following smoking a cigarette, chewing gum, or drinking coffee were investigated to underline the usefulness of this new approach.
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An intensive accumulation of thiophene derivatives occurs during the first days of development in Tagetes seedlings. After that, the thiophene content (related to dry weight) decreases to reach low values until the twelfth day of growth. High performance liquid chromatography analyses performed on cotyledons, on hypocotyls, and on roots of normal-grown and of partly-etiolated seedlings showed that bithienylbutinen, the major compound in hypocotyls and roots, is accumulated earlier than the other thiophene derivatives. The synthesis of acetoxybutinylbithiophene seems to be light-induced. This compound is not found in cotyledons. Hydroxybutinylbithiophene is synthesized specifically in the roots, α-terthiophene in cotyledons. The results obtained indicate a high intensity of thiophene metabolism in these particular organs during seedling development.
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Herbicide-treated soybean [Glycine max(L.) Merr. var. “Amsoy”] leaves and intact plants formed NO and NO2 within the leaves and released them into the surrounding atmosphere. These gaseous products are thought to be due to reactions between herbicide-caused free nitrite accumulations and plant metabolites. Untreated soybean leaves and plants did not accumulate free nitrite nor evolve these nitrogen oxide gases. At relatively low concentrations of free nitrite in green leaves only NO was detected. Higher nitrite concentrations were required for NO2 evolution. Emissions of NO and NO2 were proportional to the amount of herbicide used. The technique for detection and measurement of NOx emissions from soybean plants is described.
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We investigated the volatile organic compounds emanated from the hand of two individuals, on-line by secondary electrospray ionization-mass spectrometry in positive ionization mode. The background ambient air is continuously sampled, ionized and readily mass analyzed. When the probe samples above the headspace of the hand of two subjects, several peaks (63 for one subject and 37 for the other) arise above the background with masses reaching up to m/z 348. In spite of the different patterns, they share 30 common peaks. Some of these compounds have been assigned by collision-induced-dissociation, most of them as amines, including the amino acid ornithine.
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A new analytical strategy based on mass spectrometry fingerprinting combined with the NIST-MS search program for pattern recognition is evaluated and validated. A case study dealing with the tracing of the geographical origin of virgin olive oils (VOOs) proves the capabilities of mass spectrometry fingerprinting coupled with NIST-MS search program for classification. The volatile profiles of 220 VOOs from Liguria and other Mediterranean regions were analysed by secondary electrospray ionization-mass spectrometry (SESI-MS). MS spectra of VOOs were classified according to their origin by the freeware NIST-MS search v 2.0. The NIST classification results were compared to well-known pattern recognition techniques, such as linear discriminant analysis (LDA), partial least-squares discriminant analysis (PLS-DA), k-nearest neighbours (kNN), and counter-propagation artificial neural networks (CP-ANN). The NIST-MS search program predicted correctly 96% of the Ligurian VOOs and 92% of the non-Ligurian ones of an external independent data set; outperforming the traditional chemometric techniques (prediction abilities in the external validation achieved by kNN were 88% and 84% for the Ligurian and non-Ligurian categories respectively). This proves that the NIST-MS search software is a useful classification tool.
Article
We first summarize the early work by Fenn and colleagues on vapor ionization by an electrospray cloud (subsequently dubbed secondary electrospray ionization, or SESI), followed by analysis via an atmospheric pressure ionization mass spectrometer (API-MS). It was in part reported in Ph.D. theses and presented to ASMS conferences, but remains largely unpublished. After spending 20 years in limbo, various aspects of their method have begun to be used, leading recently to outstanding limits of detection of ambient volatiles (parts per quadrillion; ppq). There is still much room for improvement of the method, as the ionization probability (defined as the concentration ratio ns/nv between ionized vapor and neutral vapor) is p ∼ 10−3–10−4. This result follows from recent approximate measurements, as well as from a newly derived expression for the equilibrium value pe under space charge dominated conditions typical of an ES cloud (probably also of a corona discharge): pe = kɛo/(Zsq). This simple expression is derived from a balance between space charge dilution (dns/dt = −Zsnsniq/ɛo) and the rate of ionization of neutral vapor (dns/dt = knvni). It is independent of the concentration ni of the charging drops (or ions), but depends on the electrical mobility Zs of the ionized vapor and the net charge q on the charging species (ions or drops). ɛo is the electrical permittivity of vacuum. Still unresolved is the important mechanistic issue of whether the charge-exchange rate coefficient k corresponds to vapor collisions with ES drops (kd), or rather with individual ions formed after complete drop evaporation (kp, based on the ion-induced-dipole interaction model). Coincidentally, an upper limit obtained for kd is comparable to kp. The ionization efficiency of SESI is compared to that of radioactive and corona sources. Appendices include information on the various rate coefficients fixing pe. They extend the ion-induced-dipole interaction model to account for the relatively large size of most vapor molecules of interest. Size effects on kp are found to be modest, in contrast with the strong size dependence of the mobility of large ions.Graphical abstractThe development of John Fenn's 1986 proposal to use an electrospray cloud to ionize atmospheric vapors for mass spectrometric analysis is reviewed.View high quality image (131K)Research highlights► Vapors ionize readily by contact with an electrospray cloud (SESI). ► The approach is particularly useful in conjunction to API-MS. ► Both techniques have been strongly influenced by Fenn's work. ► The equilibrium ionization probability in the space charge limit is obtained.
Article
In secondary electrospray ionization (SESI) systems, gaseous analytes exposed to an elecrospray plume become ionized after charge is transferred from the charging electrosprayed particles to the sample species. Current SESI systems have shown a certain potential. However, their ionization efficiency is limited by space charge repulsion and by the high sample flows required to prevent vapor dilution. As a result, they have a poor conversion ratio of vapor into ions. We have developed and tested a new SESI configuration, termed low-flow SESI, that permits the reduction of the required sample flows. Although the ion to vapor concentration ratio is limited, the ionic flow to sample vapor flow ratio theoretically is not. The new ionizer is coupled to a planar differential mobility analyzer (DMA) and requires only 0.2 lpm of vapor sample flow to produce 3.5 lpm of ionic flow. The achieved ionization efficiency is 1/700 (one ion for every 700 molecules) for TNT and, thus, compared with previous SESI ionizers coupled with atmospheric pressure ionization-mass spectrometry (API-MS) (Mesonero, E.; Sillero, J. A.; Hernández, M.; Fernandez de la Mora, J. Philadelphia PA, 2009) has been improved by a large factor of at least 50-100 (our measurements indicate 70). The new ionizer coupled with the planar DMA and a triple quadrupole mass spectrometer (ABSciex API5000) requires only 20 fg (50 million molecules) to produce a discernible signal after mobility and MS(2) analysis.
Article
In this study, we use an ion funnel (IF) at ambient pressure to enhance the sensitivity of secondary electrospray ionization (SESI). Atenolol, salbutamol and cocaine as test compounds are delivered to the SESI interface in the gas phase and are charged with three nano electrosprays. In our experiments, we show that the compounds can be detected at concentrations in the low pptv range, which is an increase of two orders of magnitude compared with the results without the IF. With a standard SESI interface, the compounds could not be detected at all. With the use of the SESI IF interface for the headspace analysis of bananas and limes, we can detect many more compounds and at higher intensities than with a standard SESI interface.
Article
Proton transfer reaction-mass spectrometry (PTR-MS) was applied to the analysis of a series of volatile organic compounds (VOCs) that emit from various plants. These include a group of alcohols (methanol, ethanol and butanol), carbonyl-containing compounds (acetic acid, acetone and benzaldehyde), isoprene, acetonitrile, tetrahydrofuran (THF), pyrazine, toluene and xylene and a series of terpenes (p-cymene, camphene, 2-carene, limonene, β-myrcene, α-pinene, β-pinene, γ-tepinene and terpinolene) and oxygen-containing terpenes (1,8-cineole and linalool). These mass spectral data were compared to an electron ionization (EI) database identifying that not all PTR-MS fragments were common to EI. PTR-MS studies of these reference compounds were utilized to identify VOCs emitted from Eucalyptus grandis leaf at a temperature range of 30–100 °C. In addition to protonated molecules (M + H)+, abundant proton-bound dimers or trimers were detected for alcohols, acetone, acetonitrile and THF. Abundant fragment ions attributed to the loss of water from these proton-bound clusters were also observed. The stability of butyl (C4H9+m/z 57) and acetyl (CH3CO+m/z 43) fragment ions directed the proton-transfer reactions of butanol and acetic acid. Abundant (M + H)+ ions were detected for pyrazine, THF, toluene and xylene, as well as for all terpenes except those containing oxygen. For linalool and 1,8-cineole, the loss of water generated an abundant fragment ion at m/z 137. PTR-MS fragmentation patterns for terpenes were proposed for m/z 81 (C6H9+), 93 (C7H9+), 95 (C7H11+), 107 (C8H11+), 109 (C8H13+), 119 (C9H11+), 121 (C9H13+) and 137 (loss of water for oxygen-containing terpenes; C10H17+). The relative abundances of (M + H)+ and fragments for all terpenes (except linalool) were dependent on the drift tube voltage and the optimum voltage for detection of molecular ions was different for various terpenes.
Article
The present status of knowledge of the gas-phase reactions of inorganic Ox, HOx and NOx species and of selected classes of volatile organic compounds (VOCs) [alkanes, alkenes, aromatic hydrocarbons, oxygen-containing VOCs and nitrogen-containing VOCs] and their degradation products in the troposphere is discussed. There is now a good qualitative and, in a number of areas, quantitative understanding of the tropospheric chemistry of NOx and VOCs involved in the photochemical formation of ozone. During the past five years much progress has been made in elucidating the reactions of alkoxy radicals, the mechanisms of the gas-phase reactions of O3 with alkenes, and the mechanisms and products of the OH radical-initiated reactions of aromatic hydrocarbons, and further progress is expected. However, there are still areas of uncertainty which impact the ability to accurately model the formation of ozone in urban, rural and regional areas, and these include a need for: rate constants and mechanisms of the reactions of organic peroxy () radicals with NO, NO3 radicals, HO2 radicals and other radicals; organic nitrate yields from the reactions of radicals with NO, preferably as a function of temperature and pressure; the reaction rates of alkoxy radicals for decomposition, isomerization, and reaction with O2, especially for alkoxy radicals other than those formed from alkanes and alkenes; the detailed mechanisms of the reactions of O3 with alkenes and VOCs containing >CC< bonds; the mechanisms and products of the reactions of OH-aromatic adducts with O2 and NO2; the tropospheric chemistry of many oxygenated VOCs formed as first-generation products of VOC photooxidations; and a quantitative understanding of the reaction sequences leading to products which gas/particle partition and lead to secondary organic aerosol formation.
Article
The purpose of this short review is to describe the origins and the principles of operation of selected-ion flow-tube mass spectrometry (SIFT-MS) and proton-transfer-reaction mass spectrometry (PTR-MS), and their application to the analysis of biogenic volatile organic compounds (BVOCs) in ambient air, the humid air (headspace) above biological samples, and other samples. We briefly review the ion chemistry that underpins these analytical methods, which allows accurate analyses. We pay attention to the inherently uncomplicated sampling methodologies that allow on-line, real-time analyses, obviating sample collection into bags or onto traps, which can compromise samples. Whilst these techniques have been applied successfully to the analysis of a wide variety of media, we give just a few examples of data, including for the analysis of BVOCs that are present in tropospheric air and those emitted by plants, in exhaled breath and in the headspace above cell and bacterial cultures (which assist clinical diagnosis and therapeutic monitoring), and the products of combustion. The very wide dynamic ranges of real-time analyses of BVOCs in air achieved by SIFT-MS and PTR-MS from sub-ppbv to tens of ppmv - ensure that these analytical methods will be applied to many other media, especially when combined with gas-chromatography methods, as recently trialed. (C) 2011 Elsevier Ltd. All rights reserved.
Article
We report on on-line breath gas analysis with a new type of analytical instrument, which represents the next generation of proton-transfer-reaction mass spectrometers. This time-of-flight mass spectrometer in combination with the soft proton-transfer-reaction ionization (PTR-TOF) offers numerous advantages for the sensitive detection of volatile organic compounds and overcomes several limitations. First, a time-of-flight instrument allows for a measurement of a complete mass spectrum within a fraction of a second. Second, a high mass resolving power enables the separation of isobaric molecules and the identification of their chemical composition. We present the first on-line breath measurements with a PTR-TOF and demonstrate the advantages for on-line breath analysis. In combination with buffered end-tidal (BET) sampling, we obtain a complete mass spectrum up to 320 Th within one exhalation with a signal-to-noise ratio sufficient to measure down to pptv levels. We exploit the high mass resolving power to identify the main components in the breath composition of several healthy volunteers.
Article
Individual biotic and abiotic stresses, such as high temperature, high light and herbivore attack, are well known to increase the emission of volatile organic compounds from plants. Much less is known about the effect of multiple, co-occurring stress factors, despite the fact that multiple stresses are probably the rule under natural conditions. Here, after briefly summarizing the basic effects of single stress factors on the volatile emission of plants, we survey the influence of multiple stresses. When two or more stresses co-occur their effects are sometimes additive, while in other cases the influence of one stress has priority. Further investigations on the effects of multiple stress factors will improve our understanding of the patterns and functions of plant volatile emission.
Article
A thermal desorption unit has been interfaced to an electrospray ionization-ion mobility-time-of-flight mass spectrometer. The interface was evaluated using a mixture of six model volatile organic compounds which showed detection limits of <1 ng sample loaded onto a thermal desorption tube packed with Tenax, equivalent to sampled concentrations of 4 microg L(-1). Thermal desorption profiles were observed for all of the compounds, and ion mobility-mass spectrometry separations were used to resolve the probe compound responses from each other. The combination of temperature programmed thermal desorption and ion mobility improved the response of selected species against background ions. Analysis of breath samples resulted in the identification of breath metabolites, based on ion mobility and accurate mass measurement using siloxane peaks identified during the analysis as internal lockmasses.
Article
The diversity of thiophenes (natural biocides) and the differences between the concentrations of these compounds in the leaves and roots of Tagetes erecta L., T. patula L. cv. Nana furia, and T. minuta L. (marigolds) indicated the presence of at least two different sites of accumulation: leaves and roots. Leaf explants of Tagetes, however, are used by preference to obtain callus cultures. Once subcultured, secondary (C2) calli of T. patula obtained from leaves of 4 to 7-week-old plants, contained higher amounts of accumulated thiophenes (up to 80% of the amounts in the leaves) than original (C1) or twice subcultured calli (C3). The concentrations of thiophenes in C2 calli of T. minuta were about half those of C1 calli, while the concentrations of thiophenes of C1 calli amounted to 1-2% of the leaf values. Most of the C3 calli of T. minuta did not contain thiophenes at all. Although C1 calli of T. erecta also contained considerable amounts of thiophenes, the C2 calli died, most likely owing to high levels of accumulated polyphenolic compounds. The combination of species effects and the physiological state of plants and calli provides adequate information to decide whether Tagetes calli are able to produce thiophenes or not. It is concluded that the ability to produce thiophenes does not depend on the organ used, but on the genetic information present in the species, and on the physiological state of plants and calli, particularly their age.
Article
Vapors released by the skin in the hand of one human subject are detected in real time by sampling them directly from the ambient gas surrounding the hand, ionizing them by secondary electrospray ionization (SESI, via contact with the charged cloud from an electrospray source), and analyzing them in a mass spectrometer with an atmospheric pressure source (API-MS). This gas-phase approach is complementary to alternative on-line surface ionization methods such as DESI and DART. A dominating peak of lactic acid and a complete series of saturated and singly unsaturated fatty acids (C(12) to C(18)) are observed, in accordance with previous off-line studies by gas chromatography-mass spectrometry. Several other metabolites have been identified, including ketomonocarboxylic and hydroxymonocarboxylic acids.
Article
We determine the sensitivity of several commercial atmospheric pressure ionization mass spectrometers towards ambient vapors, ionized by contact with an electrospray of acidified or ammoniated solvent, a technique often referred to as secondary electrospray ionization (SESI). Although a record limit of detection of 0.2 x 10(-12) atmospheres (0.2 ppt) is found for explosives such as PETN and 0.4 ppt for TNT (without preconcentration), this still implies the need for some 10(8)-10(9) vapor molecules/s for positive identification of explosives. This extremely inefficient use of sample is partly due to low charging probability ( approximately 10(-4)), finite ion transmission, and counting probability in the mass spectrometer (1/10 in quadrupoles), and a variable combination of duty cycle and background noise responsible typically for a 10(3) factor loss of useful signal.
Article
Real time analysis of human breath is achieved in an atmospheric pressure ionization mass spectrometer (API-MS) by negatively charging exhaled vapors via contact with an electrospray cloud. The spectrum observed is dominated by a wide range of deprotonated fatty acids, including saturated chains up to C14. Above C14, the background from cutaneous sources becomes dominant. We also tentatively identify a series of unsaturated fatty acids (C7-C10), ketomonocarboxylic acids (C6-C10), and a family of aldehydes. The ionization probability of large fatty acids increases drastically when the humidity changes from 20% to 95%. Accordingly, distinguishing lung vapors (humid) from those in the background (dry) requires special precautions. Estimated fatty acid vapor concentrations in breath based on our measurements ( approximately 100 ppt) are in fair agreement with values expected from blood concentrations in the range for which data are available (C3-C6).
Article
With the invention of electrospray ionization and matrix-assisted laser desorption/ionization, scientists employing modern mass spectrometry naturally face new challenges with respect to background interferences and contaminants that might not play a significant role in traditional or other analytical techniques. Efforts to continuously minimize sample volumes and measurable concentrations increase the need to understand where these interferences come from, how they can be identified, and if they can be eliminated. Knowledge of identity enables their use as internal calibrants for accurate mass measurements. This review/tutorial summarizes current literature on reported contaminants and introduces a number of novel interferences that have been observed and identified in our laboratories over the past decade. These include both compounds of proteinaceous and non-proteinaceous nature. In the supplemental data a spreadsheet is provided that contains a searchable ion list of all compounds identified to date.
Article
A secondary electrospray ionization (SESI) method was developed as a nonradioactive ionization source for ion mobility spectrometry (IMS). This SESI method relied on the gas-phase interaction between charged particles created by electrospray ionization (ESI) and neutral gaseous sample molecules. Mass spectrometry (MS) was used as the detection method after ion mobility separation for ion identification. Preliminary investigations focussed on understanding the ionization process of SESI. The performance of ESI-IMS and SESI-IMS for illicit drug detection was evaluated by determining the analytical figures of merit. In general, SESI had a higher ionization efficiency for small volatile molecules compared with the electrospray method. The potential of developing a universal interface for both GC- and LC-MS with an addition stage of mobility separation was demonstrated.