The combination of the fast, ultra-sensitive Vocus PTR-TOF and this 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.
Marc Pfander, Lingfei Hu, Meng Ye, and Matthias Erb, Institute of Plant Sciences, University of Bern, Switzerland
Manuel Hutterli and Felipe Lopez, TOFWERK, Thun, Switzerland
The interactions of plants with their environment determines 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. Time-resolved monitoring of VOC exposure and emissions for large numbers of individual plants is critical for understanding the dynamic roles and mechanisms of VOC-dependent plant-environment interactions.
Traditionally, plant scientists collect trace level VOCs on traps and then measurement them offline with gas chromatography (GC). This process is notoriously slow, with a single sample typically taking more than 30 min to analyze, thus limiting the total number of samples which may be included in a study. The Vocus PTR-TOF mass spectrometer provides fast, real-time VOC measurements at ultra–low concentrations while preserving molecular identity – therefore no prior concentration, separation, or sample preparation is needed. The Vocus PTR-TOF is thus well suited for real-time measurement of the fragrances which plants release and perceive. In addition to enabling highly time-resolved measurements of VOC emissions from single sources (or single plants), the speed and sensitivity of the Vocus PTR-TOF creates the possibility to sample many plants in a very short time as a form of high throughput phenotyping.
In the context of an ongoing research collaboration between the University of Bern Institute of Plant Sciences and TOFWERK, with support from Abon Life Sciences and Bibus AG, a Vocus PTR-TOF was integrated into a newly developed autosampler (patent pending) to study VOC kinetics of 102 plants in a near-simultaneous fashion (see feature image above). During operation, each volatile source containing a plant is purged by a clean air flow that carries the emitted VOCs directly to the Vocus PTR-TOF for analysis. The autosampler then cycles between individual containers, measuring VOC emissions and plant responses to different stimulants, treatments, or environmental conditions. In this experiment each plant is measured for 15 seconds with a <5 second transition between samples. Complete mass spectra (0-500 Th) are saved and plotted at 5 Hz (for example, Figure 1).
Figure 2 presents the results for 1 of 17 individual plants during a 10-hour experiment measuring the plants kinetic response to a simulated attack from Spodoptera littoralis larvae which eat maize leaves. The plant responds by emitting a variety of VOCs with different kinetics, some of which can be perceived as warning cues by other plants.
This work was funded through the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (ERC-2016-STG 714239 to M. Erb).
Want to see the auto sampler in action? The following video shows the application of our autosampler for the measurement of VOC emitted from plants.