A proton transfer reaction mass spectrometer (PTR-MS) with sub-ppt limits of detection and mass resolving power up to 15000
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.
Webinar: Vocus PTR-TOF Real-time VOC Analysis with Market Leading Performance
| Sensitivity cps/ppb xylene |
Limit of Detection (LOD) 1-minute / 1-second, BTX |
Resolving Power at Specified Sensitivitya M/ΔM |
Size | Power | |
| Vocus S | 10000 | <1 ppt / < 10 ppt | 5000 | mass: 120 kg volume < 0.35 m3 480 x 615 x 1130 mm |
< 900 W (500 W typical) |
| Vocus C compact |
10000 | <1 ppt / < 10 ppt | 1000 | mass: 120 kg volume < 0.35 m3 |
< 900 W (500 W typical) |
| Vocus 2R high resolution |
10000 | <1 ppt / < 10 ppt | 10000 | mass: 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.
| Sample Flow Rate | 50-500 sccm typical 150 sccm |
| Operating Pressure | 0.5 – 5 mbar typical 1-2 mbar |
| Axial Gradient | Uniform linear field 0-5 V/mm |
| Reagent Ions | (H2O)nH3O+, NO+, O2+ |
Key Advantages of Proton Transfer Reaction Mass Spectrometry (PTR-MS) · Real-time and simultaneous detection of hundreds of VOCs · Lowest… Read More »
The interactions of plants with their environment determine their survival in nature and yields in agriculture. Plants can release specific VOCs (volatile organic compounds) to attract beneficial organisms and can detect VOCs as environmental cues. As part of an ongoing research collaboration between the University of Bern Institute of Plant Sciences and TOFWERK, a Vocus PTR-TOF was integrated into a newly developed autosampler. The combination of the fast, ultra-sensitive Vocus PTR-TOF and a novel autosampler, allows quasi-simultaneous, real-time monitoring of over 100 samples with a single mass spectrometer – providing a unique solution for VOC research in plant science and other fields.
The breadth of compounds detectable by PTR-MS can hinder analysis of samples containing large numbers of VOCs. If isobars, which have the same nominal mass, are not resolved by the mass analyzer one cannot confidently identify unknown compounds or quantify specific VOCs of interest.
Coffee is known to contain a complex mixture of VOCs that affect flavor, aroma, and color. The head space of coffee was analyzed by direct sampling into the inlet of a VOCUS 2R. The recorded mass spectrum contained thousands of unique peaks, with multiple isobaric peaks resolved at most nominal masses. Comparison of the results to simulations of data measured with reduced resolution demonstrates that confident analysis of complex VOC mixtures demands the high resolving power of the Vocus 2R.
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Characterization of compounds in human breath emissions can be used for non-invasive diagnosis of diseases, assessment of physiological functions, therapy control, and pharmacokinetic studies. Human breath emissions contains hundreds of VOCs, many at trace concentration levels. Analysis demands ultra-low detection limits, broad dynamic range, and fast time response. In this work, human breath was directly measured throughout the ingestion of a RicolaTM herb cough drop. The 13 herbs in these cough drops each have their own aroma compounds at concentrations spanning many orders of magnitude. The data capture sub-second changes in VOCs ranging from ppt to ppm concentrations.
Read moreTogether with our partner Aerodyne Research, we recently deployed a Vocus 2R to the CESAR observatory in the Netherlands for participation in an ACTRIS intensive PTR-MS intercomparison. ACTRIS (Aerosols, Clouds and Trace gases Research Infrastructure) is an initiative to coordinate the efforts of European researchers in order to produce and share high-quality observations of aerosols, clouds and trace gases. This 2-week campaign aimed to evaluate and compare best practices for PTR-MS calibration and background subtraction so as to improve measurement accuracy and precision of key atmospheric VOCs. The Vocus 2R ran alongside 11 other PTR-MS at the CESAR observatory, 8 of which also used TOFWERK TOF mass analyzers.
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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.
