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.   The instrument combines TOFWERK’s novel Vocus proton transfer reaction cell with our high performance time-of-flight technology to offer you market leading sensitivity and mass resolving power.

  • 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
  • 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
  • Automated Reagent Ion Switching. Switching between H3O+, NO+, O2+ and NH4+ expands the breadth of detectable compounds and resolves isomers
  • Interchangeable Ion Sources.  Built on our API-TOF platform, the Vocus PTR-TOF allows you to interchange the Vocus PTR reaction cell with an array of other ion sources.  
  • Adaptable for Your Applications. Work with us to integrate the Vocus PTR-TOF into your existing sampling systems and workflows
  • Field-Ready Hardware. Compact, durable architecture brings laboratory-grade performance to challenging environments
  • Intuitive, Powerful Software. Easy-to-use data acquisition interface and Tofware graphical post-processing software for the analysis of high-resolution TOF data

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
Max / Typical
2R100001 ppt  / 10 ppt 1000015000160 kg
< 0.45 m3
480 x 615 x 1480 mm
600 / 590 W
100001 ppt  / 10 ppt50007000 120 kg
 < 0.35 m3
480 x 615 x 1130 mm
600 / 590 W
M500 <5 ppt, 1 min20002500 120 kg
 < 0.35 m3
480 x 615 x 1130 mm
600 / 590 W 
Elf50020 ppt, 1 min500750 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.


Sub-ppt limits of detection in seconds Calculated as 3 times the standard deviation of signal with ultra clean air and assuming the sensitivity of BTX.


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 Rate50-500 sccm typical 100 sccm
Operating Pressure0.5 – 5 mbar typical 1-2 mbar
Axial GradientUniform linear field 0-5 V/mm
Reagent IonsH3O+, NO+,O2+, NH4+



  • Standby valve to allow servicing of Vocus reaction cell hardware without venting
  • 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 
  • Tofware data post processing
  • Library of detectable compounds 
  • Thuner automatic mass spectrometer tuning software
  • Touch screen control
  • Shipping container for deployment with no disassembly required


  • Liquid calibration system (LCS), with dedicated controls in Acquility software 
  • GC or fast-GC, control and method definition with Acquility software   
  • Aerosol inlet, including automated switching between measurements of gas, particle-phase, and zeroes 
  • Headspace autosampler, sequence editing and GC and/or MS synchronization with Acquility software
  • Permeation sources for internal mass calibration 
  • Interchangeable ion sources.  Learn more about how our API-TOF platform allows easy interchange of ion sources. 

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 Physics, in review 2019. DOI: 10.5194/10.5194/acp-2019-741 
  2. 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, in review 2019. DOI:10.5194/amt-2018-446 


  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. 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 Focus \ DOI: 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.