The Vocus PTR-TOF offers unmatched sensitivity and mass resolving power for online detection of VOCs

A proton transfer reaction mass spectrometer (PTR-MS) with sub-ppt limits of detection and mass resolving power up to 15000

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Advantages of the Vocus PTR-TOF 

The Vocus PTR-TOF is a proton transfer reaction mass spectrometer (PTR-MS) for sensitive, real-time detection of volatile organic compounds (VOCs) in industrial, laboratory, and field applications.   

  • Ultra-Low Limits of Detection.  High sensitivity and low backgrounds combine to yield sub-ppt VOC limits of detection in seconds
  • Highest Available Mass Resolving Power.  Mass resolving power up to 15000 enables identification of isobaric compounds in complex mixtures
  • Mobile Measurement. Compact, durable architecture brings laboratory-grade performance to vehicle and aircraft-based measurements
  • Adaptable for Your Applications. Work with us to integrate the Vocus PTR-TOF into your existing sampling systems and workflows
  • Intuitive, Powerful Software. Easy-to-use data acquisition interface and Tofware graphical post-processing software for the analysis of high-resolution TOF data
  • Revolutionary PTR Reaction Cell Design.  The proprietary Vocus reaction cell reduces wall losses and focuses ions to give you up to 10x the sensitivity of other commercial PTR-MS. Learn more about the Vocus technology


Webinar: Vocus PTR-TOF Real-time VOC Analysis with Market Leading Performance

Webinar: Vocus PTR-TOF Real-time VOC Analysis with Market Leading Performance

Download Vocus PTR-TOF Brochure

Improving PTR-MS without Compromise

The unique Vocus ion molecule reactor (IMR) improves almost all aspects of PTR-MS performance, while maintaining critical specifications and reaction processes that have been established for conventional designs.  

These fundamental aspects of Vocus PTR-TOF performance are key to its fast, ultra-sensitive measurement of trace VOCs.

Low Product Ion Energies

The RF focusing fields in the Vocus ion molecule reactor improve sensitivity while maintaining product ion energies and recorded branching ratios that are nearly identical to those of traditional drift-tube PTR ion-molecule reactor designs. Read More »

High Purity Reactant Ions

Vocus PTR-TOF mass spectra are dominated by protonated peaks and free of significant contributions from non-PTR reaction and therefore easily interpreted and quantified. Read More »

Simple Calibration

The Vocus PTR-TOF routinely detects a very large number of VOCs, including many for which standards are not available.  It is possible to calibrate for all detected compounds with good accuracy based on simple measurements of a small number of VOC standards. Read More »

Ultra-Fast Time Response

The combination of its efficient inlet system, heated reaction cell, and high sensitivity makes the Vocus PTR-TOF the optimum detector for high throughput or highly time resolved measurements of low volatility organic compounds. Read More »

Select a Vocus Model to Meet Your Measurement Needs

  Sensitivity cps/ppb
Limit of Detection (LOD)
1-min / 1-s, xylene
Resolving Power at  Specified Sensitivitya
Resolving Power
Size Power
Max / Typical
2R 30001 1 ppt  / 10 ppt  10000 15000 160 kg
< 0.45 m3
480 x 615 x 1480 mm
600 / 590 W
30001 1 ppt  / 10 ppt 5000 7000  120 kg
 < 0.35 m3
480 x 615 x 1130 mm
600 / 590 W
4000  5 ppt, 1 min 3500 4000  120 kg
 < 0.35 m3
480 x 615 x 1130 mm
600 / 590 W 
500 20 ppt, 1 min 500 750  55 kg
< 0.125 m3
 380 x 500 x 650 mm
450 /400 W 

a. Each model can be operated with higher resolving power at reduced sensitivity.   



  • Standby Valve.  Allows servicing of Vocus reaction cell hardware without venting (Models 2R, S, and Scout). 
  • Tofware Data Post Processing.
  • Library of Detectable Compounds.
  • Thuner Software. Automatic mass spectrometer tuning software.
  • Touch Screen Control.
  • Shipping Container.  Deployment with no disassembly required.
  • Acquility Data Acquisition and Instrument Control Software.
    • Automated gas calibration and zeroing with programmable cycling   
    • Real-time reporting of calibrated concentrations for target compounds
    • Single-click transitions between shutdown, ready, and sleep states 



Vocus Reaction Cell and Sampling Inlet

  • Proprietary reagent ion source and ion-molecule reaction cell with axial DC field and RF-focusing.
  • Automated reagent ion switching.
  • Temperature controlled reaction cell, ambient temperature up to 120C.
  • Heated inlet system, up to 180 C.
  Sample Flow Rate 50-500 sccm typical 100 sccm
  Operating Pressure 0.5 – 5 mbar typical 1-2 mbar
  Axial Gradient Uniform linear field 0-5 V/mm
  Reagent Ions H3O+, NO+,O2+, NH4+


Vocus PTR-TOF Publications


  1.  Li, H.; et al. Terpenes and their oxidation products in the French Landes forest: insight from Vocus PTR-TOF measurements. Atmospheric Chemistry and Physics2020. In Focus | DOI: 10.5194/acp-20-1941-2020 


  1. Holzinger, R.; et al. Validity and limitations of simple reaction kinetics to calculate concentrations of organic compounds from ion counts in PTR-MS. Atmos. Meas. Tech. Discuss. 2019. DOI: 10.5194/amt-12-6193-2019


  1. Riva, M.; Rantala, P.; Krechmer, J. E.; Peräkylä, O.; Zhang, Y.; Heikkinen, L.; Garmash, O.; Yan, C.; Kulmala, M.; Worsnop, D.; and Ehn, M. Evaluating the performance of five different chemical ionization techniques for detecting gaseous oxygenated organic species. Atmos. Meas. Tech. Discuss. 2018.  In Focus | DOI:10.5194/amt-12-2403-2019
  2. Krechmer, J.; Lopez-Hilfiker, F; et al. Evaluation of a New Vocus Reagent-Ion Source and Focusing Ion-Molecule Reactor for use in Proton-Transfer-Reaction Mass Spectrometry. Analytical Chemistry 2018. In FocusDOI: 10.1021/acs.analchem.8b02641

Application Notes

Conference Presentations

Customer Research

TOFWERK Publications


White Papers

Product Information

Vocus is a Leap Forward in PTR Reaction Cell Design


Traditional PTR reaction cell designs use a stack of metal lenses connected by a series of resistors to produce a linear drift field. The stable, tuneable drift field (E) enables precise control over the distribution of water clusters and the electrostatic reaction time. But, because of scattering and diffusion within the drift tube, many analyte ions are not transmitted out of the drift tube toward the mass analyzer – thereby limiting the achieved sensitivity.

The Vocus reaction cell maintains the operation parameters required for fast, quantitative PTR analysis, with two unique design features that significantly increase sensitivity. By superimposing an oscillating RF field on top of a DC field, analyte ions are focused toward the center axis of the reaction cell and efficiently transmitted into the mass analyzer. The reaction cell is built using a resistive glass tube, rather than the traditional lens stack. This allows the application of the RF focusing field, while producing a more uniform DC field than the traditional lens stack.

Read more about the Vocus reaction cell design and performance in Krechmer, Lopez-Hilfiker, et al, Analytical Chemistry, 2018.