Frequently Asked Questions

PTR-MS stands for Proton Transfer Reaction - Mass Spectrometry. It is a highly sensitive analytical technique that allows for the real-time measurement of volatile organic compounds (VOCs) at ultra-low concentrations. Originally pioneered by scientists at the University of Innsbruck and the founders of IONICON, the technology has been continuously advanced and commercialized globally by our company.

PTR-MS uses a soft chemical ionization process. Inside a drift tube, hydronium ions (H₃O⁺) interact with sample molecules that have a higher proton affinity than water. During this interaction, a proton transfers from H₃O⁺ to the target molecule (M), forming a protonated product ion (MH⁺). This soft ionization minimizes fragmentation, making mass spectra much easier to interpret.

Nowadays, PTR-MS instruments are solely being built with time of flight mass spectrometers which due to their high mass resolving power can separate between isobars, hence allow for identification of compounds having the same nominal mass. This is a major advantage compared to earlier PTR-MS instruments based on quadrupole MS or state of the art SIFT-MS instruments which are still only available with quadrupole mass filters. 

The Selective Reagent Ionization – Mass Spectrometry (SRI-MS) technology allows for identification of even some isomers. With the fastGC add-on IONICON instruments now have GC capabilities - chemical separation in combination with real-time measurements. Unique to PTR-MS – and a major advantage over e.g. SIFT-MS – is the capability to change the energy levels in the drift tube, which suppresses or increases fragmentation. Distinct fragmentation patters that are observed by varying this energy levels (E/N) foster the identification capabilities of IONICON PTR-MS further. This method is used in our air monitoring solutions as part of the advanced pattern-matching AME (Automated Measurement and Evaluation) software.

SRI-MS stands for Selective Reagent Ionization Mass Spectrometry. While standard PTR-MS uses H₃O⁺ ions to detect VOCs, SRI-MS allows you to switch to alternative reagent ions like NO⁺, O₂⁺, Kr⁺, Xe⁺, NH₄⁺ or CO₃^-. This enables the detection of molecules that don't react with H₃O⁺ (like certain inorganic compounds) and helps separate isomeric compounds by yielding different product ions. Learn more…

PTR is a soft chemical ionization process, which means that in contrast to electron impact or charge transfer ionization the fragmentation rates can be kept very low. Therefore, absolute concentrations can be derived immediately. In addition, common compounds of ambient air do not get ionized, which makes mass spectra easily interpretable and accounts for very low online detection limits in the pptv-range.

Unlike SIFT-MS, PTR-MS does not dilute low concentrated samples by any carrier gas and lose precursor ions to the mass filter between the source and the drift tube, hence PTR-MS is much more sensitive, has a lower detection limit and does not need any gas supply (proton transfer from H₃O⁺ ions). Our instruments are light-weight and space-saving which clearly puts us ahead of technologies like SIFT-MS. Moreover, only PTR-MS is available in a range of time-of-flight (TOF) based PTR-TOF instruments which has a lot of advantages. Last but not least, unlike with SIFT-MS, energy levels (E/N) in the drift tube can be varied in PTR-MS, catering to better identification capabilities. PTR-MS and SIFT share a common history. Learn more about the evolution from SIFT to PTR-TOF which resulted in ultimate performance and technological perfection.

Adjusting the E/N ratio allows you to precisely control the amount of fragmentation that occurs during ionization. By systematically changing these energy levels, you can induce specific fragmentation patterns that act as 'fingerprints' to help identify unknown compounds and separate complex isomers. This powerful analytical dimension is only possible with a uniform drift tube design and part of the powerful AME (Automated Measurement and Evaluation) software.

Unlike standard GC-MS, PTR-MS does not require sample pretreatment, trapping, or pre-concentration. It measures VOCs online and in absolute real-time, providing instant results over a massive dynamic range (down to sub-pptv levels). While GC-MS is excellent for offline chemical separation, it involves significant time delays. For applications requiring instant feedback, high-throughput, or dynamic monitoring, PTR-MS is superior.

PTR-MS is generally much more sensitive than SIFT-MS. The “downside” of PTR-MS, providing only one type of precursor ions (H₃O⁺, the most important type though) has been overcome by a technology we call Selective Reagent Ionization - Mass Spectrometry (SRI-MS), where H₃O⁺, NO⁺ and O2⁺ can be produced in the IONICON ion source with even higher yields than SIFT-MS. Also the possibility to use several energy levels (E/N) in the drift tube is not possible with SIFT-MS, but this feature enhances the unique substance identification capabilities of PTR-MS significantly. Compared to APCI, a widely used technology, PTR-MS allows for more accurate quantification due to a controlled and very efficient ionization, offering higher sensitivity. Compared to many other CIMS, IONICON PTR-MS has a well controlled and straightforward ionization process which results in 4 important ion-chemistry qualities only available from IONICON. Moreover, the new EVR PTR-MS technology offers the fastest response time in the CIMS market. PTR-MS is extremely versatile, used in various applications and is commercially available from IONICON.

PTR-MS has been invented by the founders of our company and now more than 25 years later, is more popular than ever before. Sometimes other instrument manufacturers call their system "PTR-MS" or "H₃O⁺ CIMS" etc. if they use proton transfer by H₃O⁺ as their primary ionization technique. But there's much more to an IONICON PTR-MS. A real PTR-MS is characterized by 4 important ion-chemistry quality dimensions which enable quantitative real-time results and are only available from IONICON. Learn more about the essentials of an IONICON-grade PTR-MS.

IONICON delivers a complete, ready-to-use solution. Every PTR-MS system includes the instrument itself, an integrated data acquisition system, our comprehensive software suite for real-time analysis, detailed documentation, and all necessary connection lines and toolkits. Additionally, the package optionally includes on-site installation and hands-on training by an IONICON or partner specialist to ensure you can start your research immediately.

As long as the instrument is turned off, it is highly portable and can be moved via mounted wheels or handrails (depending on the model). During operation, shocks should be avoided to prevent the turbo pumps from getting damaged. However, with special shock absorbing housings it is possible to use our PTR-MS devices in airplanes and other vehicles. Our engineers can work out a solution for you!

We deliver our instruments fully equipped with a 1.2 m (or longer) inlet hose consisting of an internal inert PEEK (or silcosteel) capillary, heating (up to 180°C) and thermal insulation. The flow is adjustable between 50 and up to 1000 sccm via a digital mass flow controller. Customized inlet solutions (e.g. second inlet line, different lengths or heating capacities, multiplexing systems) are available too.

Yes! Several turbo molecular pumps and membrane pumps (oil-free) are part of the system and controlled by the internal electronics. Compared to other analytical instruments, the noise level is very low. No external pumping station is necessary.

A standard PTR-MS operates without expensive carrier gases. The primary consumable is simply pure distilled water—an internal reservoir only needs refilling every few months. If your system is equipped with Selective Reagent Ionization (SRI-MS), you will also need standard gas supplies (such as O₂, NO, filtered air or other gases) for alternative precursor ion generation.

Sure! Just contact us and our experts will be happy to suggest solutions so that your solution fits your needs in every way. We have experience in designing special products tailored to your needs.

Yes! Each of our instruments has ample interfaces (please check the specifications of the instrument you are interested in). Additionally we offer interface adapters - the quantity of interfaces is scalable. Please contact us for more information.

Absolutely. All IONICON PTR-MS instruments are fully automated, PC-controlled, and network-ready via Ethernet. You can easily monitor and control your experiments remotely from anywhere. For technical assistance, our support team can use secure remote access tools (like TeamViewer) to help with tuning, troubleshooting, and software updates, ensuring minimal downtime.

Although operating a PTR-MS instrument is very simple and intuitive, we offer an installation & training package, where one of our experts will give you a training session upon delivery of the system directly at your site. Moreover, we provide continuously updated technical documentation to our customers, SOPs, video tutorials and many other resources. Individual training sessions are available on demand. Just contact our team.

PTR-MS easily detects almost all common Volatile Organic Compounds (VOCs), as they generally have a higher proton affinity than water. Crucially, the major constituents of ambient air (N₂, O₂, Ar, CO₂) have lower proton affinities and are not ionized. This lack of interference is what allows IONICON instruments to achieve market-leading, ultra-low detection limits in the sub-pptv range. Furthermore, with our Selective Reagent Ionization (SRI-MS) technology, you can switch precursor ions (e.g., to O₂⁺ or NO⁺) to detect an even broader range of inorganic and organic molecules.

Please check the Proton Affinity (PA) of your desired molecule (e.g. in databases like the NIST chemistry webbook or ask our experts). If it is higher than the PA of water (165.2 kcal/mol) it is detectable.

Yes! We are happy to invite you to our company site to give you the opportunity to test the PTR-MS technology directly with the substances you bring along. We call this: YOUR showcase. Together with our experts you can discover our products and make valuable experiments tailored to your application. We also offer analytical services, from single tests to whole studies. Just contact us and let us know how we can help.

Yes! But please be careful and use appropriate personal safety gear. Connect an appropriate exhaust line to the outlet of the instrument in order not to contaminate the lab air. The instrument's vacuum system may be contaminated though and special caution is necessary when services or maintenance shall be carried out. Please contact our experts if you have more questions or would like us help you with service and maintenance.

Every substance, no matter if solid or liquid, has a certain vapor pressure depending on its temperature. Therefore the substance is always also present in its gaseous form and can be measured as long as the concentration is above the detection limit. Our Liquid Calibration Unit (LCU) can also be used as a precise evaporation tool that allows you to create a vapor of certain liquids that you are interested in.

Yes. By coupling an IONICON PTR-TOF system with our CHARON (CHemical Analysis of aeRosol ON-line) particle inlet, you can quantitatively measure organic sub-µm particulate matter, as well as particulate ammonium and nitrate, in real-time at single-digit ng/m³ concentrations. This unique combination allows you to monitor the full spectrum of atmospheric organic carbon—from gas-phase VOCs to particle-phase semi- and low-volatile organic compounds (SVOC, LVOC)—using a single instrument.

Our systems feature highly optimized, uniformly heated inlet systems and our proprietary Enhanced Volatility Range (EVR) technology. EVR significantly minimizes memory effects and surface interactions, providing some of the fastest response times in the market for semi-volatile, 'sticky' molecules. This ensures that rapid transient events are captured accurately without signal smearing.

Yes. Isobars (molecules with the same nominal mass but different elemental formulas) can be easily separated by our high-resolution PTR-TOF instruments thanks to their high mass resolving power. Isomers (molecules with the exact same elemental formula but different structures) can be distinguished using a few advanced techniques: coupling the instrument with our fastGC add-on for rapid chemical separation, adjusting the drift tube energy levels (E/N) to observe distinct fragmentation patterns, or utilizing specific reagent ions via SRI-MS. SLIM-IMS, integrated in a PTR-TOF, a so-called PTR-SLIM-TOF, is a new technology now available, adding another dimension of data, allowing for direct separation of many isomers.

Identifying unknown compounds in complex mixtures is greatly enhanced by our Selective Reagent Ionization (SRI-MS) technology and precise E/N (drift voltage) control. By switching precursor ions (e.g., from H₃O⁺ to NO⁺ or O₂⁺), you can differentiate chemical classes—such as distinguishing isomeric aldehydes from ketones. Additionally, varying the drift tube collision energy (E/N) produces distinct fragmentation 'fingerprints' that aid in structural identification.

Standard PTR-MS (using H₃O⁺) cannot detect most alkanes because their proton affinity is lower than water. However, if your system is equipped with SRI-MS or SRI+, you can switch to reagent ions like O₂⁺, Kr⁺, or Xe⁺. These ions react via charge-transfer rather than proton-transfer, allowing you to accurately measure linear alkanes, branched hydrocarbons, and other non-polar molecules in real-time.

Yes. Our latest advanced platforms, such as the FUSION PTR-TOF and select modular systems, feature true bipolar capabilities with SRI^-. This allows researchers to switch between traditional positive ion mode (e.g., H₃O⁺) and negative ion chemical ionization (NI-CIMS). Negative mode expands your analytical capabilities to cover completely different compound classes, including inorganic acids and highly oxygenated organic molecules (HOMs).

Negative reagent ions like CO₃^-  which are part of SRI^- are highly selective and allow for the ultrasensitive detection of trace atmospheric acids (such as HNO3, H2SO4, and HCl) and highly oxygenated organic molecules (HOMs). For example, CO₃^- reacts efficiently via clustering and deprotonation, making it an essential tool for scientists studying atmospheric oxidation processes, secondary organic aerosol (SOA) formation, and halogen chemistry.

When utilizing SRI-MS, the flow of source gas (such as O2 or NO) into the ion source is extremely low, typically between 5 and 10 sccm. This equates to atmospheric-pressure gas consumption of only 0.3 to 0.6 liters per hour, ensuring your calibration and source gas cylinders last for extended periods in the field or lab.

No pretreatment is required. A major advantage of PTR-MS over offline methods like GC-MS is its ability to analyze ambient air or gas samples directly and instantly, eliminating the need for traps, pre-concentration, or complex sample preparation.

Our systems achieve ultra-fast response times of < 100 ms. Results are delivered in absolute real-time. Because our PTR-TOF systems analyze the entire mass spectrum simultaneously (unlike quadrupole based PTR-MS or SIFT-MS systems that scan sequentially), the temporal resolution is more than sufficient for highly dynamic applications like eddy covariance flux measurements.

Depending on the model, the lowest measurable concentration is below 1 pptv, typically a few pptv. FUSION PTR-TOF instruments typically have their LoD in the ppqv-range which is even lower. Have a look at our product portfolio.

The detection range is linear from 10ppmv (or for higher-sensitive PTR-TOF systems: approximately a factor 10 lower) down to the detection threshold, which is five to six orders of magnitude depending on the model. Compare our products here. If your sample has VOCs in higher concentration than upper linearity-range limit we can propose special dilutions systems, allowing to accurately quantify even higher concentrations.

In most cases, no. High humidity or rapid changes in sample humidity do not disrupt standard PTR-MS operation. Because water vapor is naturally abundant, our core H₃O⁺ ionization chemistry remains stable. For a very small subset of compounds (like formaldehyde) where the proton affinity is very close to water, humidity can slightly influence the detection limit, which our software can account for. 

We now offer the new Dynamic Humidity Control (DHC) technology, making PTR-MS humidity-independent. DHC introduces a controlled amount of water vapor into the drift tube and continuously monitors humidity levels. Based on these levels, DHC dynamically adjusts the internal water vapor levels to maintain consistent reaction conditions, regardless of the humidity in the sample gas.

Yes. Formaldehyde is challenging because its proton affinity is only slightly higher than water, leading to humidity-dependent back-reactions. This results in a somewhat higher limit of detection for formaldehyde and a minority of substances which are in the same proton affinity range than water. The reactions in this case are humidity depending.

No. When operating in standard H₃O⁺ mode, PTR-MS uses the ambient air sample itself as the buffer gas. Unlike SIFT-MS or GC-MS, the sample is not diluted by an external carrier gas (like Helium or Nitrogen). This lack of dilution is a key reason IONICON instruments achieve market-leading, ultra-low detection limits.

Yes! You can monitor concentrations online and in real-time. There is a continuous flow of sampled air through the PTR-MS system that is analyzed immediately and time of flight based instruments (e.g. PTR-TOF series) analyze the whole mass range at the same time. Thus all substances a PTR-MS can detect, are recorded continuously and in parallel, not sequentially which is the case in quadrupole based analyzers (e.g. SIFT-MS or IMR-MS).

Because of the precisely controlled ion chemistry and uniform E/N ratio in our traditional drift tube, the reaction kinetics are perfectly understood. This allows researchers to use theoretical kinetic reaction rate constants to calculate absolute concentrations directly. Systems that rely on focusing reactors do not have a uniform E/N ratio and often require constant, empirical calibration with gas standards for quantitative accuracy.

For highly accurate results, calibrations with gas standards are recommended from time to time. IONICON offers a range of sophisticated trace calibration systems, based on gas or liquid standards (LCU) and zero air or an integrated calibration system (ICS).

No! Measurements (including e.g. switching of external valves) can be done fully automated. Various safety mechanisms take care that sensitive parts are shut down automatically. Remote control tools are available.

Depending on the user's preference, the PTR-MS software displays and saves values as raw data (counts per second or Ampere) and in absolute concentrations (ppbv or µg/kg).

Operating costs are exceptionally low. During standard operation, an IONICON PTR-MS only consumes standard electric power and a few liters of distilled water per year. Because no expensive high-purity carrier gases (like Helium) are required, the total cost of ownership is a fraction of conventional analytical techniques.

Absolutely. Air Monitoring Systems like our AMCentinel and VOCentinel are purpose-built for continuous industrial monitoring (e.g., semiconductor cleanrooms, industrial fence-line monitoring). They feature standard industrial communication protocols, robust enclosures, and automated multiplexing valves to monitor multiple sampling points autonomously.

Yes! There are numerous software packages available that evolve continuously. We enclose a data acquisition software that was programmed by our in-house software department as well as the PTR-MS Viewer, a data processing tool.

A premium data analysis suit is optionally available: IONICON Data Analyzer (IDA) which is a new platform to visualize, analyze and manage your IONICON TOF-MS projects.

The optional Automated Measurement and Evaluation (AME) is our industrial monitoring software for complex set of compounds by Automating Measurement, data Evaluation, and visualization.

IONICON provides a proprietary, powerful software suite tailored for PTR-MS data. The acquisition software handles automated instrument control and real-time monitoring, while the advanced PTR-MS Viewer and Data Analyzer tools allow for sophisticated post-processing, peak identification, and high-resolution mass spectra analysis.

A premium data analysis suit is optionally available: IONICON Data Analyzer (IDA) which is a new platform to visualize, analyze and manage your IONICON TOF-MS projects.

The optional Automated Measurement and Evaluation (AME) is our industrial monitoring software for complex set of compounds by Automating Measurement, data Evaluation, and visualization.

Yes! External devices (e.g. electronic valves, flow controllers etc.) can be controlled via the PTR-MS software. This allows e.g. automated switching between different samples during a long-term measurement. The PTR-MS software is undergoing continuous improvements and there other external devices such a certain multiplexing valves that can also be controlled with our software. Please ask if you have special requirements.

IONICON PTR-MS systems are designed for robust, long-term operation with minimal maintenance. Routine tasks primarily include refilling the internal distilled water reservoir every few months and occasionally inspecting the inlet lines and cleaning or replacing the ion source. Because our systems use dry, oil-free vacuum pumps, messy and frequent pump maintenance is eliminated.

Yes! We offer maintenance contracts for our systems that cover the regular service work. We can propose very flexible service offers that are adapted to your budget. Our specialists do the maintenance work quickly and efficiently, ensuring that your system is configured and operated in optimal conditions. Please contact us if you want to know more about it.

No! PTR-MS instruments have exceptionally long maintenance intervals in the range of up to six months.

We take long-term customer relationships seriously. IONICON provides comprehensive, fast-response support for troubleshooting, software updates, and experimental design. Because our instruments are fully network-capable, our engineers can routinely perform secure remote diagnostics and tuning via TeamViewer, ensuring maximum uptime for your research. Visit customer support!