Ionization for analysis of low volatility species in air
SUPER SESI enables in-vivo studies of different biological systems, such as human breath, human skin, mice breath analysis, cell cultures, and plants. SUPER SESI is particularly optimized for Breath analysis of heavy metabolites in real time. Specific responses to controlled stimuli can be easily identified thanks to the fast response of the ionizer, which enables kinetic studies. This allows the variables of interest to be differentiated from other confounding variables. SUPER SESI is coupled with a mass spectrometer and analyzes airborne molecules and metabolites, which evaporate naturally at minute concentrations. SUPER SESI handles low volatility species and ionizes them with high ionization efficiency and very low background levels.
High quality data
Results with biological & statistical relevance
The human body is extremely complex. Each metabolite plays very specific functions, sometimes at very low concentrations. Differentiating these metabolites, other bodily species, and other confounding variables, is key to understand the roles of the different molecules.
The purpose of SUPER SESI is to assist researchers in understanding the roles of the different species. Conclusive research in biology requires great amounts of high-quality data.
- Low Limits of detection allow for the analysis of low volatility species. In practice, this means that larger and more biologically significant molecules can be detected. SUPER SESI, coupled with High-Resolution Mass Spectrometry (HRMS), routinely detects species in breath with concentrations in the ppt range and vapor pressures as low as 10-7 and 10-8 Thousands of species are detected in each exhalation.
- High resolution is required to differentiate and identify all the species detected. SUPER SESI is optimized for High-resolution Mass Spectrometers, which separate the different species detected.
- High speed is required to produced large data sets, which are required in biological research to obtain statistically significant results. A SUPER SESI – HRMS measurement can be completed in seconds, with virtually no sample treatment. High speed enables real-time analysis and high throughput.
- SUPER SESI HRMS generates great amounts of data. For this reason, data-mining techniques are normally used to find biomarkers among all the species detected. ARIADNA is a post-processing and data mining platform that streamlines this mathematical steps so that the researcher can focus on the biological processes.
Exact identification capabilities enable for the obtained and the post-processed data to be analyzed in its bio-molecular and medical context. For example, the species in a metabolic pathway can be identified and their variations evaluated together. This is important because blind data-mining techniques alone would be vulnerable to confounding variables, especially when several features can be detected.
Principle of operation
Secondary Electro-Spray Ionization (SESI) uses a nano-electrospray that produces a cloud of charging ions. These ions ionize the vapors that are in contact with the cloud. The charge transfer reactions are specific, very efficient, and very soft (no high energies involved). As a result, SESI enables:
- a very high ionization efficiency,
- soft ionization of polar species with no fragmentation, and
- an instantaneous response.
The charging ions are highly concentrated and rapidly expanding due to coulomb repulsion. As a result, the charging ions react with the molecules of interest very rapidly before the mixture reaches its equilibrium. In this regime, the ionization efficiency is mainly limited by dilution of the neutral molecules due to mixing with the clean gas that is sampled by the mass spectrometer.
SUPER SESI features a laminar flow design that minimizes mixing. This results in very high ionization efficiencies, which translate into high sensitivities.
Improving the Limit of Detection for low volatility species
Detecting Volatile Organic Compounds (VOC’s) is very challenging because they are released into the gas stream at very low concentrations. In particular, the biologically specific metabolites that can be used to identify the different metabolic processes, tend to be large molecules with very low vapor pressure. For this reason, the detector must provide a very high sensitivity, which is defined as the minimum concentration of the analyte that produces a signal.
If sensitivity was the only limiting factor, one would expect very low volatility species (with vapor pressures in the range of 10-12 Bar) to be detectable. However, most analyzers are limited to highly volatile species. For instance, vapor pressures of Aniline and Phenol are 5·10-4 Bar and 8·10-4 Bar, respectively. which are much higher than the theoretically expected limit of 10-12 Bar for a sensitivity in the ppt level. This mismatch of over seven orders of magnitude shows that the Limits of Detection (LoD) are constraint by other effects.
SUPER SESI routinely detects 4-hydroxy-2-hexadecenal in human breath when coupled with Orbitrap. The vapor pressure of this compound at bodily temperature is 2.7·10-7 Bar (estimated with the Clausius-Clapeyron relation). This illustrates that, in practice, SESI-MS is over three orders of magnitude more powerful than other real time VOC analyzers that detect species with vapor pressures in the 10-4 Bar range, such as Aniline and Phenol.
The sensitivity of SUPER SESI-MS is below the ppt level, and yet, the species with vapor pressures in the 10-12 Bar range are still not detected. This shows that there is still a lot of room for improvement. Currently, background levels and condensation effects are the limiting factors defining the LoD for low volatility species.
Table 1 shows some of the species that can be commonly detected and identified in breath with the SUPER SESI - QExactive platform. These species were previously verified by LC-HRMS of breath condensate. SUPER SESI routinely detects and identifies species with vapor pressures in the range of 10-7 to 10-8 Bar.
(*) The signal intensities in this table correspond to one single exhalation of one person in a SUPER SESI – Qexactive platform. Breath measured in a different moment or a different person will most likely produce different signal intensities. This table is provided to illustrate the possibilities of the SUPER SESI – QExactive system. It does not reflect any performance threshold.
(**) The vapor pressure was estimated using the Clausius-Clapeyron relation. The boiling temperature @ 1 Bar and the enthalpy of vaporization were estimated with ACD/Labs Percepta Predictors data, available at Chemspider.com (The Royal society of Chemistry).
Detecting low volatility species
Large molecules with low volatility are often more specific from a biological standpoint, but they are more difficult to detect because they tend to condensate in the inner walls of the ionizer. This produces a background signal that deteriorates the limits of detection:
- SUPER SESI works at high temperature to reduce condensation and adsorption.
- It is internally coated to minimize the chemical interaction.
- The flow path is designed to maintain a laminar flow, which minimizes convective transport of species towards the walls.
- The internal geometry is designed to minimize the area exposed to the vapors.
- The ionization chamber can be easily opened, and all parts of the chamber are readily accessible and can be cleaned in a very rapid operation.
Through the auxiliary port, SUPER SESI provides a controlled flow of gas that can be used to sweep the species of interest to the ionization region. In the example below, the auxiliary gas is introduced in a flask with red wine, which is also connected to the sample line. The red and green spectra correspond with the wine and the background. A few peaks dominate the wine spectrum, but a closer zoom discovers a very rich variety of compounds that make wine aroma so rich in nuances. The gas is not bubbling inside the flask, as the aerosols formed would contaminate the ionizer.
Gas sampling bags
Gas Sampling bags can be directly coupled to the SUPER SESI to analyze their content. Using BagDesampler is recommended to improve the repeatability, and to improve the signals of the low volatility species.
BagDesampler is a gas tight chamber that controls the conditions for introducing the bag gas into the SUPER SESI.
- Bags are preheated to a constant temperature. Low vapor pressure species tend to condensate in the inner walls of the bag. Heating the bag releases these species, thus improving the LoD of the bag – SUPER SESI – MS system.
- BagDesampler pressurizes the bag with a constant flow of clean gas. This improves the repeatability of the process
- BagDesampler uses the clean aux gas, which is already interfaced by the SUPER SESI. No extra sources of gas are required. This minimizes cross contamination problems.
Simplicity and robustness
Designed to be easily integrated in your workflow
SUPER SESI incorporates all the components and controls in one single unit. It is ready to connect with the MS and start analyzing.
Ambient samples may carry aerosols that can contaminate and clog the electrospray capillary. For this reason, a nano-ampere meter is used to evaluate the stability of the electrospray.
SUPER SESI is designed so that the capillary can be easily replaced in les than two minutes without the need for any tool. The goal is to minimize the impact of this on the productivity of the laboratory.
Optimized designs compatible with Thermo Fisher and Sciex Instruments
SUPER SESI is compatible with Thermo Fisher and Sciex mass spectrometers. Please contact us to verify compatibility with your mass spectrometer.
SESI-MS provides a sensitivity below the ppt level, routinely detecting species with vapor pressures of 10-7 Bar. At this level, the complexity of most samples is humongous. The required separation capacity depends on each application, but empirical results show that the resolving power required to differentiate all the species that can be detected is above 70.000. This requirement is expected to become more restringing as the sensitivity and the minimum vapor pressure that can be detected are improved.
Currently, Orbitrap are the most commonly used mass spectrometers that routinely provide MS spectra with resolving power exceeding 150.000. For this reason, the first SUPER SESI was designed specifically for Orbitrap. However, the mass spectrometry market is rapidly evolving. High Resolution Time of Flight (HRToF) provide resolutions in the range of 80.000, and it is expected that they will reach 100.000 over the next years. A new SUPER SESI specifically designed to be coupled with the Triple ToF API 5600 commercialized by Sciex is currently being developed to enable SESI-HRToF.
Installation, training, and technical service
Your success is our success
The impact we have on our customers' success will directly impact our own success.
All SUPER SESI units are thoroughly tested before delivery. Once the SUPER SESI is at the facility of the customer, a FIT’s specialist goes the customer’s laboratory to provide initial installation and training. Training takes three days and covers all aspects required to operate the SUPER SESI.
Once the installation is completed, technical support will be provided via email, telephone, and Skype. In the event that the system malfunctions, FIT and the customer will do their best to identify the problem. FIT will provide the most convenient way to fix the SUPER SESI as soon as possible.
Optimized designs compatible with Thermo Fisher and Sciex Instruments
SUPER SESI for Thermo is currently in production. We can adapt each unit for your research goals. Please contact us to find out how we can help you.