Ambient Mass Spectrometry
Ambient mass spectrometry methods address the need for rapid analysis with minimal sample preparation. In our laboratory, we use two main approaches to form gas-phase ions at ambient conditions: secondary electrospray ionization and plasma-based ionization methods.
Secondary Electrospray Ionization Mass Spectrometry (SESI-MS)
Electrospray is a widely used ionization technique to bring analytes from solution into the gas phase. While this is its primary use in mass spectrometry, electrosprays offer an opportunity to ionize gaseous analytes (i.e. vapors). This variant of electrospray ionization has been dubbed secondary electrospray ionization, whereby neutral vapors interacting with an electrospray plume of pure solvent are readily ionized and subsequently mass analyzed.
One main advantage of this approach is that it offers the opportunity to monitor gaseous analytes in real time. SESI can detect a very wide range of compounds. In particular, it is possible to not only detected positively charged ions, formed, for example from amino acids but also negatively charged ions, e.g., from fatty acids. When SESI is combined with state-of-the-art mass spectrometers, low limits of detection are achievable without any sample pre-concentration (external page i.e., low parts-per-trillion by volume (pptv) for certain metabolic compounds). We exploit this feature in our lab in a number of projects which require fast mass spectrometric analysis of vapors at trace concentrations. Currently two types of SESI ion sources are commercially available (external page from SEADM and external page from FIT) which both were developped by researchers from our lab.
Current Projects:
Exhaled breath contains a wealth of biochemical information, which can be used for a number of purposes. Globally, one of the main goals in our group is to advocate the use of breath as an alternative body fluid for untargeted metabolomic studies. For example, consistent with previous metabolomic studies, we have found that exhaled breath shows temporal fluctuations, probably reflecting circadian patterns. In addition, despite this temporal ''noise'', we have found that each individual shows a distinct breath-print stable over time. This is also in agreement with prior work from urine metabolomics studies. Ongoing collaborations with the University Hospital Zurich and the Children's University Hospital Zurich are devoted to non-invasively diagnosing respiratory diseases and monitoring drugs in exhaled breath. We have so far reported breath markers for COPD, OSA, and IPF. The ongoing studies focus on lung cancer, cystic fibrosis, and asthma as well as in-vitro pathogen cultures. Drug metabolite studies with ketamine in mice and salbutamol in humans showed the benefits of having a high time resolution when tracing drug metabolites directly in exhaled breath. We have recently started to investigate sleep with continuous monitoring during the night with SESI-HRMS.
Untargeted metabolomic studies usually result in a pool of statistically significant m/z features, which may be useful for diagnostic purposes. However, the chemical identity of these features is rarely clear, which results in a huge loss of useful biological information. It is our aim to overcome this lack of information by identifying the metabolites responsible for the different m/z features previously established in breath analysis. To accomplish this goal, we apply several methods, such as collection and upconcentration of exhaled breath condensate samples, which subsequently are analyzed by liquid chromatography-mass spectrometry. In this way, proper identification of unknowns is possible by measuring the exact mass, the chromatographic retention times, and fragment mass spectra, which can be compared to proposed pure reference standards.
Wordwide, around two-thirds of the population suffers from lactose intolerance. In Switzerland, 1 in 5 people is affected. Symptoms usually appear after consuming milk or dairy products and include nausea, bloating, flatulence, abdominal pain and diarrhea. Current diagnostics however, lack sensitivity and specificity for lactose intolerance. Symptoms often do not correlate with the experienced symptoms. The Lactobreath project aims to provide a rapid, non-invasive and accurate breath test based on SESI-HRMS to diagnose lactose intolerance. We are conducting a clinical trial using real-time breath analysis combined with genetic testing, hydrogen breath test, intestinal gas measurements, urinary metabolites and symptom assessment to identify and link metabolic breath profiles to each clinical trait. If you are interested in participating, you can find more information on our dedicated Lactobreath page.
Small metabolites reflect phenotype and carry information for exchange between the host and its gut microbiota. For the moment, most of the MS-based metabolomics approaches applied in the field of the microbiome are based on sampling (feces, plasma, or tissue samples from the host), which is usually time-consuming, highly variable, and does not allow measurements with high time resolution. We aim to provide a non-invasive method to monitor the metabolic changes of the host-microbiota ecosystem simultaneously and in real-time. We use SESI-MS in combination with home-built headspace sampling devices and isotope-labeled carbon sources to trace the metabolism of anaerobic bacterial cultures, bees, and mice.
Untargeted direct-infusion (DI) metabolomics, such as breath analysis with SESI-MS has significant advantages, e.g., it’s a real-time and rapid technique. Our group is dedicated to improving the technique methodologically with advanced acquisition strategies, for example, by overcoming limitations of ion trap instruments for more sensitive metabolite detection or by improved fragmentation techniques for better characterization of biomarkers. Recently our group developed a new method to separate chimeric MS2 spectra in DI-MS called incremental quadrupole acquisition to resolve overlapping spectra short IQAROS. Further research is performed to improve these techniques constantly.
Ruminants are essential to the global food systems, converting human-inedible biomass into high-quality animal protein due to the rumen microbial ecosystem. Understanding ruminal fermentation is key to improve the efficiency of resource utilization and sustainability of ruminant production systems. Currently, the assessment of rumen fermentation relies on invasive sampling procedures that impair animal welfare. We use SESI-HR-MS to characterize dairy cows’ exhalome and specifically to identify the exhaled volatile fatty acid profile as a proxy for ruminal volatile fatty acids. This method shows potential for a new avenue for ruminant research without compromising animal well-being.
We aim to improve the current knowledge of off-line breath analysis by thoroughly examining materials used to produce gas sampling bags, in which breath is stored for later analysis. We compare the physical properties and storage capabilities of the most commonly used materials, such as PTFE, Tedlar and Nalophan, on various metabolites found in human breath.
Blood measurements are invasive and must be sent to an analytical laboratory after sampling. Breath, conversely, can be sampled nearly endlessly without stress for humans. On-line measurement of breath with SESI makes it even possible to get instantaneous results. With SESI, we can detect a wide range of volatile organic compounds (VOC) in human exhaled breath. Some of these compounds are exogenously originating from the environment that was inhaled and exhaled again. Other compounds are human metabolites and are transferred from the blood into the respiratory tract, where they get exhaled. One focus of the group is to find specific biomarkers that can be measured in blood and breath and their correlation.
Quantification of metabolites present within exhaled breath is a significant challenge for on-line breath analysis. It is also essential for gauging the measuring technology's analytical performance, accuracy, reproducibility, reliability, and stability. To quantify exhaled breath metabolites of interest, we utilize a range of built-in-house or commercial systems for the controllable generation of gaseous standards in a chemical environment simulating human exhaled breath. By generating calibration curves of detected metabolites of interest using reference material, we can provide quantitative information for these specific metabolites. We recently developed a modular, dynamic vapor generator that operates at various relative humidity levels and generates gaseous standards of either a single compound or mixtures in the concentration range from low ppt to high ppm in a controllable, repeatable and consistent way. In particular, we quantified short-chain fatty acids (SCFA) in the gas phase, which are key bioactive components in the gut produced by dietary components. We are also developing a system to quantify non-volatile compounds found in the form of exhaled aerosol particles.