Detection of axillary perspiration metabolites using ion mobility spectrometry coupled to rapid gas chromatography.

The composition of human sweat-and as a consequence the composition of volatiles released from human skin-strongly depends on genetic preconditions, diet, stress, personal hygiene but also on health status and medication. Accordingly, the composition is a carrier of information on the physical and mental states of a person. Therefore, rapid on-site analysis of the relevant substances may be used for medical diagnosis and medication control or even for psychological characterisation. Ion mobility spectrometry coupled to rapid gas chromatography (GC-IMS) was applied to the analysis of human axillary sweat as a sensitive, selective, rapid, and non-invasive method in a feasibility study. For this purpose, a sampling chamber was designed and manufactured. The design and the experimental setup were validated successfully. At least 179 human metabolites could be detected by GC-IMS from the skin of 7 volunteers. Fifteen metabolites were available in all samples from all volunteers and therefore can be characterised as basic sweat compounds which might enable the localisation of hidden persons. Furthermore, in a preliminary feasibility study, the potential of GC-IMS for differentiating the composition of sweat after physical exercises and in a stressful situation-even gender specific-could be demonstrated. Thus, with GC-IMS, a rapid and mobile analytical tool for the analysis of skin volatiles is available for a broad range of applications, e.g. with regard to axillary odour, human health, nutrition, consumption of remedies or drugs of abuse, the localisation of trapped or hidden persons, or even the characterisation of the reaction on stressful situations. Graphical abstract.

GC-IMS headspace analyses allow early recognition of bacterial growth and rapid pathogen differentiation in standard blood cultures.

Outcome of patients with blood stream infections (BSI) depends on the rapid initiation of adequate antibiotic therapy, which relies on the fast and reliable identification of the underlying pathogen. Blood cultures (BC) using CO2-sensitive colorimetric indicators and subsequent microbiological culturing are the diagnostic gold standard but turnaround times range between 24 and 48 h. The detection of volatile organic compounds of microbial origin (mVOC) has been described as a feasible method for identifying microbial growth and to differentiate between several microbial species. In this study, we aimed to investigate the ability of mVOC analyses using a gas chromatograph coupled to an ion mobility spectrometer (GC-IMS) for the recognition of bacterial growth and bacterial differentiation in BCs. Therefore, samples of whole blood and diluted bacterial suspension were injected into aerobic and anaerobic BC bottles and incubated for 8 h. Headspace samples from cultures of Escherichia coli (DSM 25944), Staphylococcus aureus (DSM 13661), and Pseudomonas aeruginosa (DSM 1117) were investigated hourly and we determined at which point of time a differentiation between the bacteria was possible. We found specific mVOC signals in the headspace over growing BCs of all three bacterial species. GC-IMS headspace analyses allowed faster recognition of bacterial growth than the colorimetric indicator of the BCs. A differentiation between the three investigated species was possible after 6 h of incubation with a high reliability in the principal component analysis. We concluded that GC-IMS headspace analyses could be a helpful method for the rapid detection and identification of bacteria in BSI.

Medium Vacuum Electron Emitter as Soft Atmospheric Pressure Chemical Ionization Source for Organic Molecules.

An electron emitter as a soft atmospheric pressure chemical ionization source is presented, which operates at inner pressures of the device in the medium vacuum range (>10(-3) hPa). Conventional nonradioactive electron emitters require high vacuum (<10(-6) hPa) to prevent electrical sparkovers. The emitter presented here contains structural modifications of an existing setup, which inhibits electrical breakdowns up to 10(-2) hPa at 8 kV acceleration voltage. The increased inner pressure reduces the ionization efficiency until 10(-3) hPa-achievable without a turbomolecular pump-by 2% compared to high-vacuum conditions. This can be compensated with an increase of the electron source output. The functionality of this ion source is demonstrated with mass spectrometric and ion mobility measurements of acetone, eucalyptol, and diisopropyl methanephosphonate. Additional mass spectrometric measurements of 20 different organic compounds demonstrate the soft characteristics of this ionization source.

Tuning Soft Ionization Strength for Organic Mass Spectrometry.

Besides the progress of new mass spectrometer technologies, the investigation and development of soft ionization sources play an important key role for analytical sciences. Since the dielectric barrier discharge ionization (DBDI) is identified as two temporally separated events, a selective prevention of the coincident plasma can lead to improved ionization strength. Although a DBDI is known as a soft ionization source, a modulation of the high-voltage amplitude and duty cycle can lead to optimized ionization strength. This is an advantage to cover different types of analytes.

Dielectric Barrier Discharge Ionization of Perfluorinated Compounds.

The soft ionization ability based on plasma-jet protonation of molecules initiated by a dielectric barrier discharge ionization source (DBDI) is certainly an interesting application for analytical chemistry. Since the change of an applied sinusoidal voltage may lead to different discharge modes the applied discharge was powered by a square wave generator in order to get a homogeneous plasma. It is known that besides the protonation [M+H](+) of unpolar as well as some polar molecules the homogeneous DBDI can be used to ionize molecules directly [M](+). Here we prove that the DBDI can be applied to exchange fluorine by oxygen of perfluorinated compounds (PFC). PFC are organofluorine compounds with carbon-fluorine and carbon-carbon bonds only but no carbon-hydrogen bonds. While the position of the introduction into the plasma-jet is essential, PFC can be measured in the negative mass spectrometer (MS) mode.

Dataset of volatile organic compound emission patterns from flowers and damaged leaves recorded with gas-chromatography coupled ion mobility spectrometry.

Plants emit a range of volatile organic compounds (VOCs) as a way of interacting with their biotic and abiotic surroundings. These VOCs can have various ecological functions, such as attracting pollinators, repelling herbivores, or may be emitted in response to abiotic stress. For the present dataset, we used gas chromatography coupled ion mobility spectrometry (GC-IMS) to analyse the VOCs emitted by different plant species under controlled conditions. GC-IMS is a rapid and sensitive technique for gas phase analysis, that separates VOCs based on their retention time and drift time, resulting in characteristic heatmaps where the xy-position of a signal corresponds to compound identity, while signal intensity reflects its abundance. In this dataset, rapid analysis by GC-IMS was used to record emission pattern of 140 plant species from different taxonomic groups. This includes both floral volatiles and emission from leaves after induced damage. The data was pre-evaluated and listed in one table, containing information on the plant material used, as well as information on the respective emission patterns (including already identified compounds). Thus, this dataset provides a broad overview over plant VOC emissions. These can be used to either check the distribution of knowns substances, or the specific emissions of plants for functional, ecological or physiological studies or as the starting point for chemotaxonomic studies. The extraordinary ease with which these data can be generated - with the suitable set-up - lends itself to larger scale systematic or ecological studies across plant (or animal) groups and even ecosystems.

Evaluation of floral volatile patterns in the genus Narcissus using gas chromatography-coupled ion mobility spectrometry.

Premise: Daffodils (Narcissus, Amaryllidaceae) are iconic ornamentals with a complex floral biology and many fragrant species; however, little is known about floral plant volatile organic compounds (pVOCs) across the genus and additional sampling is desirable. The present study investigates whether the floral scent of 20 species of Narcissus can be characterized using gas chromatography-coupled ion mobility spectrometry (GC-IMS), with the aim of building a comparative pVOC data set for ecological and evolutionary studies. Methods: We used a commercial GC-IMS equipped with an integrated in-line enrichment system for a fast, sensitive, and automated pVOC analysis. This facilitates qualitative and (semi)-quantitative measurements without sample preparation. Results: The GC-IMS provided detailed data on floral pVOCs in Narcissus with very short sampling times and without floral enclosure. A wide range of compounds was recorded and partially identified. The retrieved pVOC patterns showed a good agreement with published data, and five "chemotypes" were characterized as characteristic combinations of floral volatiles. Discussion: The GC-IMS setup can be applied to rapidly generate large amounts of pVOC data with high sensitivity and selectivity. The preliminary data on Narcissus obtained here indicate both considerable pVOC variability and a good correspondence of the pVOC patterns with infrageneric classification, supporting the hypothesis that floral scent could represent a considerable phylogenetic signal.

Hyphenation of a MEMS based pre-concentrator and GC-IMS.

A micro-electro-mechanical system (MEMS) based pre-concentrator filled with a standard Tenax TA adsorbent as well as with a synthetic receptor designed to adsorb 3-hydroxy-3-methylhexanoic acid (3H3MHA), a particular metabolite only available from human beings, was adapted to a custom made ion mobility spectrometer with gas-chromatographic pre-separation (GC-IMS). This combination was compared to a traditional sample loop GC-IMS. The application of a pre-concentrator is highly beneficial for the GC-IMS as analysing technique. By variation of the adsorbed sample volume, the system can be adapted to changing sample concentration ranges easily, thus increasing sensitivity significantly. Detection limits of few hundred ppqV could be obtained in this work for eucalyptol and 3 human metabolites (benzaldehyde, 2-ethyl-1-hexanol and decanal) as exemplary analytes. Moreover, the appropriate choice of selective pre-concentration phases in the pre-concentrator enables an adaptation of sampling to the composition of the mixture. Relevant compounds in very low concentrations can be amplified by using specially designed cavitands while interfering substances could be suppressed. This was successfully demonstrated by detecting 3H3MHA, a compound exclusively available in human sweat, which can be used to locate trapped or hidden individuals.

Coupling laser desorption with gas chromatography and ion mobility spectrometry for improved olive oil characterisation.

The investigation of volatile compounds in the headspace of liquid samples can often be used for detailed and non-destructive characterisation of the sample. This has great potential for process control or the characterisation of food samples, such as olive oil. We investigated, for the first time, the plume of substances released from olive oil droplets by laser desorption in a feasibility study and applied ion mobility spectrometry coupled to rapid GC pre-separation to enhance selectivity. Our investigation demonstrated that significantly more substances can be detected and quantified via laser desorption than in the usual headspace, enabling a rapid (5-10 min), sensitive (low ng/g range) and comprehensive analysis of the sample, with the potential for quality control and fraud identification. Therefore, laser desorption provides a useful sampling tool for characterising liquids in many applications, requiring only a few µL of sample.

On the potential of ion mobility spectrometry coupled to GC pre-separation - A tutorial.

In this tutorial, we want to demonstrate the significant potential of ion mobility spectrometry (IMS), an analytical technique for identification and quantification of gas-phase compounds, in particular combined to other useful analytical tools. Coupled to gas-chromatographic pre-separation (GC-IMS), selectivity can be improved significantly, thus enabling the analysis of complex, humid mixtures. In-line pre-concentration can improve sensitivity down to the ppqV range. Furthermore, the use of non-radioactive ionisation sources in the near future could gain acceptance and will avoid legal restrictions. Hence, with suitable and controlled sampling, implementation of appropriate substance and pattern databases and data evaluation software, GC-IMS as rapid, selective and sensitive analytical tool has shown its high potential for many applications in process and quality control, medicine (diagnostics, medication and therapy control), biology, safety and security. In the present tutorial, we want to demonstrate this capacity on behalf of examples from the application fields mentioned above, with particular focus on controlled sampling, pre-concentration and pre-separation as well as on data treatment and interpretation.