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) that is used 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+ 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

Select a Model to Meet Your Measurement Needs

 Sensitivity cps/ppb xyleneLimit of Detection (LOD) 1-minute / 1-second, BTXResolving Power at  Specified Sensitivitya M/ΔMSizePower
 Vocus S 10000<1 ppt  / < 10 ppt5000mass: 120 kg volume < 0.35 m3 480 x 615 x 1130 mm< 900 W (500 W typical)
 Vocus C compact10000<1 ppt  / < 10 ppt1000mass: 120 kg volume < 0.35 m3< 900 W (500 W typical)
 Vocus 2R  high resolution10000<1 ppt  / < 10 ppt 10000mass: 160 kg volume < 0.45 m3 480 x 615 x 1480 mm< 1100 W (600 W typical)

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

  • Heated inlet system up to 180 C
  • Temperature controlled water vapor source
  • Proprietary reagent ion source and ion-molecule reaction cell with RF-focusing
  • Automated reagent ion switching
  • Temperature controlled reaction cell, 50C – 120C
Sample Flow Rate50-500 sccm typical 150 sccm
Operating Pressure0.5 – 5 mbar typical 1-2 mbar
Axial GradientUniform linear field 0-5 V/mm
Reagent IonsH3O+, NO+, O2+



  • Online, automated gas calibration 
  • Liquid calibration unit (optional)
  • GC or Fast-GC coupling interface (optional)
  • Standby valve to allow servicing of Vocus reaction cell hardware without venting
  • Data acquisition, data post processing, and automatic mass spectrometer tuning software
  • Touch screen control
  • Shipping container for deployment with no disassembly required
  • Interchangeable ion sources.  Learn more about how our API-TOF platform allows easy interchange of ion sources.  (optional)

Vocus PTR-TOF Publications

2018 J. Krechmer and F. Lopez-Hilfiker, 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

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.