Soil Gas Analysis

Online and Standard Methods for Efficient and Simple Soil Gas Analysis

Background

Soil Gas Analysis

Underground contaminants from sources such as landfill wastes (known as landfill gas (LFG)), mining activities, and petroleum hydrocarbons produce gas that diffuses through the soil and is the released into buildings and the atmosphere. This gas includes volatile organic compounds (VOCs), produced from anaerobic digestion of organic waste. Many VOCs can be toxic and/or odorous, so the effect of soil gas emissions on ambient air, subsurface vapor migration, and subsurface vapor intrusion into buildings needs to be quantified.

Several environmental agencies have issued guidance and protocols for measurements of soil gas. Sampling and analysis of soil gas is challenging because samples may have high heat and humidity, VOCs are complex and diverse, and matrix effects can affect the analysis.

The Vocus PTR-TOF offers a solution for online VOC analysis. The high resolving power enables identification of individual compounds within complex soil gas emissions, without any sample preparation or GC separation, leading to a real-time and fast data output. These features of Vocus PTR-TOF make in situ measurements of soil gas emissions efficient and simple. The system can also be used in the lab for analyzing gas samples in bags or canisters.

The EI-TOF for GC system can be used for GC-MS methods with the US EPA TO-15 method or US EPA “guidance for evaluating landfill gas emissions from closed or abandoned facilities.”  This system has high mass resolving power and high mass accuracy, acquires simultaneous full mass spectra, and separates isobaric ions for confident identification. The high sensitivity of EI-TOF mass spectrometer can reduce the need of large sampling volumes for VOCs and make sampling easier and more efficient.

Solutions

  • Real-Time VOC Analysis Using the Vocus PTR-TOF

    • Highest sensitivity available with sub-ppt limits of detection
    • High mass resolving power enables identification of individual compounds within complex mixtures
    • Real-time and fast data output capturing rapid changes in VOC concentrations and suitable for mobile monitoring
    • Full spectrum acquisition allows measurements of wide range of compounds simultaneously

    What is PTR-MS?

    Example time series of ambient xylene concentrations recorded with the PTR-TOF 2R at 2 Hz. The inset demonstrates the precision and fast response during a period when concentrations were between 150 and 350 pptv.

  • Standard Offline GC-MS Method Analysis Using the EI-TOF coupled with GC

    • High mass resolving power allows separation of isobaric ions
    • High mass accuracy enables confident identification and separates interferences
    • Ultra-sensitive detection for sub- trace VOCs
    • Outstanding spectrum quality simplifies matching to NIST library
    • High peak capacity when used in a GCxGC configuration

    500 ppb Mixture of CFCs and Hydrocarbons using CTOF GC-TOF

    A 5-min GC analysis of a 50 ppb hydrocarbon and CFC mixture

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