Volatile Organic Compounds (VOCs): Analysis of Biogenic Emissions Using Mass Spectrometry

The key source of most volatile organic compounds (VOCs) present in the atmosphere is biogenic emissions. These biogenic volatile organic compounds (BVOCs) include oxygenated organic compounds such as hexenal, acetone, acetic acid, and methanol, as well as hydrocarbons such as monoterpenes, sesquiterpenes, and isoprene. They have a major contribution in atmospheric chemistry as well as in the development of secondary aerosol (SOA) and ozone production.

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Proton Transfer Reaction - Mass Spectrometry

Proton transfer reaction (PTR) is ideal for measuring both BVOCs and previously unforeseen compounds. Earlier, the atmosphere-ecosystem exchange of only very few BVOCs has been explored. With ultra-fast analysis capabilities and high-time resolution, the IONICON PTR-TOFMS series products can perform eddy-covariance measurements for studies of the active atmosphere-ecosystem exchange of a wide range of BVOCs. This capability helps in gathering further knowledge about the atmospheric VOC budget.

PTR-MS - Trace Gas Analysis in Real-Time

The IONICON PTR-MS systems are the most sensitive instruments for real-time monitoring of hundreds of VOCs, such as acetone, methanol, acetaldehyde, ethanol, toluene, benzene, xylene and many others, including certain inorganic compounds, present in the air.

The ionization by Proton Transfer Reaction (PTR) has a number of benefits;

  • Very efficient - high sensitivity with LODs < 1 pptv
  • Does not require pre-separation, such as GC
  • Sample preparation is not necessary
  • Very soft - with little to no and adjustable fragmentation

Together this enables trace gas analysis in real-time

Eddy Covariance Technique

The eddy covariance technique, also termed as eddy correlation and eddy flux technique, performs measurements and calculations of vertical turbulent fluxes existing in the atmosphere. This method needs highly time-resolved 3D wind component measurements.

A parallel measurement of VOC concentrations can be correlated with the vertical wind component for extraction of emission and deposition fluxes. For this purpose, a trace gas analyzer should be capable of quantitatively measuring ultra-low VOC concentrations at a high-time resolution of 10 Hz. These fundamentals of eddy covariance flux measurements are impeccably fulfilled by the PTR-TOFMS series from IONICON.


IONICON’s PTR-TOFMS Series delivers high time resolution measurements faster than 10 Hz and can produce quantitative measurements for trace gas concentrations because of its high sensitivity. In each measurement, the IONICON PTR-TOF instruments gather the whole spectrum and obtain information about a wide variety of existing BVOCs.

Thanks to high mass resolving power, the PTR-TOFMS Series can also separate isobars and perform chemical identification of the compounds of interest. The IONICON PTR-TOFMS technology is already a reliable method for numerous scientists involved in the atmospheric research.

IONICON PTR-MS Soft Ionization Technology

The innovative IONICON PTR-MS soft ionization technology (Figure 1) ionizes all compounds that possess a proton affinity (PA) higher than water via proton transfer from H3O+. Atmospheric air constituents such as carbon dioxide, oxygen, argon, and nitrogen are not identified because of their lower PAs when compared to water. This is the main reason behind the IONICON technology’s low, real-time detection limit for trace compounds. The IONICON PTR-TOFMS comprises of precisely controlled drift tube parameters and ion source, thereby enabling absolute quantification of VOC concentrations.

The new IONICON X2 technologies feature the newest generation of performance tools including the ION-BOOSTER funnel and also the hexapole ION-GUIDE for the ultimate PTR-TOFMS experience. The ion funnel directs the ions into the hexapole ion guide which results in virtually lossless transmission of a highly focused ion beam into the TOF mass spectrometer. This increases the sensitivity greatly and also enhances the instrument’s mass resolving power. The newly introduced PTR-TOF 6000 X2 is IONICON’s current flagship model and includes the latest X2 technologies.

IONICON X2 technologies for PTR-TOFMS performance increase: ION-BOOSTER funnel and hexapole ION-GUIDE

Figure 1. IONICON X2 technologies for PTR-TOFMS performance increase: ION-BOOSTER funnel and hexapole ION-GUIDE

IONICON’s proprietary Selective Reagent Ionization - Mass Spectrometry (SRI/SRI+) technology is offered as an option with the IONICON PTR-TOFMS. It has NO+ and O2+ (SRI) or Kr+ (SRI+) as an alternative to H3O+ as precursor ions are generated in the new ULTRA-PURE ion source (patent pending). The ionization potential of Kr+ and O2+ is higher than H3O+, allowing an IONICON instrument to spot and quantify several main inorganic substances such as CH4, NO2, CO2, SO2, CO, and much more. A large quantity of isomeric VOCs can be separated and then quantified in real time with the aid of NO+ as reagent ions.

This information has been sourced, reviewed and adapted from materials provided by IONICON Analytik.

For more information on this source, please visit IONICON Analytik.


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