Close this search box.

Bring the lab anywhere.

Real-time measurement of trace compounds in air

Reactors for Flexible Ionization 

Target your compounds of interest. Vocus ionizes molecules by controlled reactions with reagent ions in a reactor.

Vocus CI-TOF Reactors

Use one reactor with a single reagent ion
OR use one reactor that can switch between multiple reagent ions in a single experiment
OR interchange two reactors with different reagent ions


The PTR reactor (Proton Transfer Reaction) is a powerful system for the analysis of a broad range of volatile organic compounds (VOCs). The proprietary Vocus PTR Reactor reduces wall losses and focuses ions with radiofrequency (RF) fields to give you maximum sensitivity and low detection limits. The Vocus PTR Reactor is further compatible with other reagent ion schemes, including ammonium adduct ionization – to target broader ranges of compounds.

Available PTR Reagent Chemistries

Reagent IonAnalyte Compound ClassesExample Applications
H3O+ (PTR)Small oxygenated compounds, polar molecules, BTEX, PAHs, other aromaticsAir quality analysis, food and flavor, environmental contamination
NH4+ Highly functionalized VOCs, oxygenated compounds, peroxidesExplosives and narcotics detection, photochemical oxidation products
NO+Alcohols, substituted aromatics, cyclic and branched alkanes, long-chain semi-volatile alkanesVehicle exhaust, wine contaminants
O2+Alkanes, carbon disulfide, ammonia, halogenated compoundsAmbient air monitoring, vehicle exhaust

The Vocus Aim Reactor offers the fast and sensitive detection of trace organic and inorganic compounds spanning the entire volatility range. The flow tube reactor operates at an increased pressure to suppress fragmentation of analyte ions and uses compact VUV sources to generate both positive and negative reagent ions. Ultra-sensitive chemical ionization through the utilization of flexible reagent ion chemistries allows sensitive and selective ionization of a variety of compounds.

Available Aim Reagent Chemistries

Reagent IonPolarityAnalyte Compound ClassesExample Applications
Iodide (I)NegativeOxygenated organics, acids, peroxides, inorganic acids, inorganic compoundsAmbient air monitoring, biomass burning, SOA formation, semiconductor, PFAS
Benzene cations (B+)PositiveVolatile hydrocarbons, DMS, ammoniaAmbient air monitoring
Protonated acetone (A+)PositiveAmines, solvents, ammoniaAmbient air monitoring
Bromide (Br)NegativeSimilar to iodide, but including iodine containing compoundsMarine emissions, iodine chemistry, inorganic acids
Ammonium (NH₄⁺)PositiveLightly oxygenated organicsAtmospheric chemistry, ambient air monitoring
Nitrate (NO3)NegativeHighly oxygenated organics, sulfuric acidAtmospheric chemistry, ambient air monitoring

Detection Suitability

With a variety of reactors and reagents, the Vocus CI-TOF provides users ultimate flexibility when targeting specific compound classes.

Detection Suitability Chart


The Vocus Aim Reactor helps to eliminate fragmentation when targeting volatile compounds.

Fragmentation Chart


The Vocus PTR enables the sensitive measurement of hydrocarbons, volatiles, and some oxidized organics with a general ionization approach with fragmentation becoming increasingly likely with increasing functionality, particularly with oxidized organic molecules.

  • Low pressure reaction cell (1-5 mbar), where the ionization takes place.
  • Optimized for protonation and charge transfer ionization, also suitable for a few positive adduct-ion chemistries.
  • Ions are generated by a discharge ion source.
  • Can measure a broad range of VOCs (Volatile organic compounds), non-negligible fragmentation for functionalized molecules, while not being dependent on humidity.

The Vocus Aim enables the measurement of an extensive range of compounds including oxidized organics, hydrocarbons, and inorganics species, by utilizing specific ion chemistries with limitless flexibility.

  • A medium pressure flow tube reaction cell (50 mbar).
  • Optimized for adduct-ion and charge transfer ionization with a suite of positive and negative reagent ions.
  • Up to three VUV ionization sources are used to generate reagent ions of positive and negative polarity.
  • For classical ions like ammonium adduct and iodide adduct, a patented water vapor suppression system allows humidity independent measurements, even at higher ionization pressures.
  • Both use the same time of flight mass spectrometer platform, including an interface that delivers molecules from the reaction cell to the TOF.
  • If you have an Aim-compatible PTR model, you can remove the PTR reactor from the front and swap it out for an Aim reactor (not available with the Vocus Elf and Eiger) or upgrade to a different reactor later if your measurement or research goals change.
  • The Aim reaction cell is optimized for adduct-ion chemistry, low-volatility, and reactive trace gases.
  • Sensitivity can be adjusted based on the concentrations of the analytes being targeted and the linear range required.
  • Multiple ion sources can be used with the Aim reactor, enabling diverse types of re agent ions to be generated to analyze a variety of molecule classes. This is particularly powerful when used with the Vocus Fast Switching series.
  • Chemical ionization at higher pressure – to facilitate adduct ion chemistry and reduce collision energies that cause fragmentation.
  • No electric field – to facilitate adduct ion chemistry and virtually eliminate frag mentation.
  • All PFA/PTFE wetted surfaces walls for improved transport of low-volatility gases.
  • Conical geometry to limit sample contact with walls and improve response times.
  • API-TOF is the mass spectrometer platform that all Vocus instruments are based on, its essentially a name change including many hardware upgrades since the days of the API-TOF.
  • Previously, you could get the IMR (Ion Molecule Reactor) to do medium-pressure chemical ionization (I.e., CIMS) or an atmospheric pressure chemical ionization with the API-TOF platform (i.e., CI-API-TOF) – Aim represents the next generation of the CIMS and CI-API-TOF technologies, with an all-in-one package which is delivered with everything you need to get started measuring.
  • Published works with the old IMR helped us understand how we can use adduct ion chemical ionization, especially iodide CIMS – this work formed the foundation for the development of the Aim reactor and associated technologies.
  • The introduction of a VUV source removed previous reliance on radioactive polonium (dangerous, inconvenient, and extremely sensitive) or x-ray (weak, low sensitivity) sources, replacing them with a non-toxic, user friendly, bright, reliable, stable, in expensive, and non-regulated reagent ion source.
  • The implementation of a conical reaction chamber and optimized flows intersection has improved turbulences in the reactor while minimizing wall interactions this improves the response time of sticky analytes.
  • The reactor is entirely made of Teflon, improving the time response of the instrument.
  • Adduct ionization sensitivity is no longer dependent on humidity.
  • Limited sampling flow and the need for carrier flow (I.e., N2) for producing the re agent ion.
  • PTR (PTR Reactor with H3O+) is a great all-purpose detector that is well documented for measuring conventional species like BTX, ketones, PAHs, polar molecules, etc., or as a first pass for non-target analysis.
  • The PTR Reactor is compatible with multiple reagent ions (O2+, NO+, and NH4+) allowing operators to switch between reagents quickly to expand their analysis or to assess the usefulness of adduct-ion chemistry (NH4+), without needing to change hardware.
  • Highly functionalized compounds (e.g., biogenic oxidation products: monomeric and dimeric species).
  • Organic and inorganic radicals.
  • Low-volatility compounds.
  • Inorganic acids.
  • Amines and ammonia.
  • Halogen-containing substances.
  • Quantifying molecules that fragment heavily with the Vocus PTR Reactor.
  • Iodide is the most used reagent, generated by photolyzing a mixture of toluene or benzene (i.e., photo absorber) and trace methyl iodide. We know it is good for detecting organic compounds with various oxygen atoms (> 3). In addition, iodide can measure inorganic acids including nitric acid, and hydrochloric acid. Here are some links to application notes and published papers.
  • Since the Aim Reactor is new, there are still a lot of reagents that have yet to be tested. Here is a list of reagents we have tried and what they can do:
    • Acetone: Suitable for amines and ammonia and compounds with a higher proton affinity than Acetone.
    • Ammonia: Suitable for VOC and OVOC species (> 1 oxygen atom).
    • Benzene: Suitable for ionizing VOC with ionization energies lower than benzene (terpenes, Toluene, Xylene) with virtually no fragmentation.
    • Bromide: Like iodide, suitable for OVOC species (> 3 oxygen atoms).
    • Acetate: Suitable for organic acid (> 3 oxygen atoms).
    • Nitrate: Suitable for highly oxygenated species (> 5-6 oxygen atoms).
    • Chlorine: Suitable for VOC and OVOC (> 2 oxygen atoms).
    • Sulfur Hexafluoride: Suitable for organic acids and inorganic species including ozone and SO2.

H3O+ (PTR): Established and widely accepted standard for the broad analysis of trace gases, applicable to air quality analysis, food and flavor, environmental contamination, and other applications.

NH4+: Suitable for the analysis of highly functionalized VOCs, oxygenated compounds, peroxides, applicable for the detection of explosives and narcotics, and photochemical oxidation products.

NO+: Suitable for the analysis of alcohols, substituted aromatics, cyclic and branched alkanes, long-chain semi-volatile alkanes, applicable for the analysis of vehicle exhaust and wine contaminants.

O2+: Suitable for the analysis of alkanes, carbon disulfide, ammonia, halogenated compounds, applicable for ambient air monitoring, and vehicle exhaust.


Contact Us Salesforce Form
Please sign me up for the TOFWERK Email Newsletter