Membrane Interface Probe (MIP)

The MIP can be driven or pushed to the depth of interest to extract and collect a VOC vapor sample that is transported via a carrier gas within a transfer line to the surface for analysis. This process can continue without having to retrieve the device between measurements unless the MIP membrane fails.

The membrane interface portion of the probe consists of a small polymer port that is permeable to gas but impermeable to liquid. The permeable port is a thin film of tetrafluoroethene (TFE) impregnated onto a stainless steel screen with an area of 37.42 mm and a thickness of 0.76 mm. The permeable port is brazed onto a steel block that also contains a resistive heater coil and a thermocouple, allowing the temperature of the membrane to be controlled and monitored. Increasing the heater temperature increases the rate of adsorption into the membrane, diffusion through the membrane, and evaporation from the membrane surface into ultra-pure-grade helium carrier gas. This carrier gas is circulated over the back of the membrane through a transfer line to a surface-mounted collection and/or detection device. Depending upon the surface configuration, the gas can be injected directly into a total measuring device (e.g., flame ionization detector, photo ionization detector, or electron capture detector), captured on an adsorbent, desorbed and injected into a GC/MS, or directly injected into a quadrupole ion trap mass spectrometer (ITMS). Speciation with the ITMS can be problematic when the gas stream contains several different chemicals of concern. Determining the depth at which the sample was taken when the sampler is in a near-continuous operating mode is more difficult the deeper the instrument is driven.

For Further Information

A Permeable Membrane Sensor for the Detection of Volatile Compounds in Soil
T. Christy.
SAGEEP 1998: Symposium on the Application of Geophysics to Engineering and Environmental Problems. Environmental and Engineering Geophysical Society, Wheat Ridge, CO, 1998

Tri-Service Site Characterization and Analysis Penetrometer System Validation of the Membrane Interface Probe
U.S. Army Corps of Engineers, 62 pp, 2002

This is a validation report on the Corps configuration of a MIP on the site characterization and analysis penetrometer system (SCAPs) mounted on a cone penetrometer technology (CPT) rig. The system uses a MIP to collect the sample and convey it to a direct-injection ion trap mass spectometer.

Plume Delineation Using Membrane Interface Probe (MIP), Savannah River Site, Aiken, South Carolina
Columbia Technologies, LLC, Baltimore, MD.
WSRC-OS-2003-00050, 69 pp, May 2003

In a 2002 investigation of subsurface contamination at the Savannah River site, Aiken, SC, MIP technology was used to delineate the depth and horizontal extent of contamination in the vadose and saturated zones, and CPT technology was used to characterize soil types.

Use of the Membrane Interface Probe (MIP) and Direct Sampling Ion Trap Mass Spectrometer (DSITMS) to Investigate a Potential Source Area at the Vint Hill Farms Station (VHFS) BRAC Site, VA
Triad Resource Center, 2005

Abstracts of Journal Articles

Accelerated VOC Source Investigation Pairing SCAPS/MIP with EPA Triad to Save Time and Money, Marine Corps Base Camp Pendleton, California

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Defining TCE Plume Source Areas Using the Membrane Interface Probe (MIP)

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Delineation of Chlorinated Solvent DNAPL and the Associated Groundwater Plume with MIP Screening

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Direct Detection of Dense Nonaqueous Phase Liquids (DNAPL) Using High Resolution Reflection Seismic Techniques at the SWMU-12 Site Charleston, Naval Weapons Station, Charleston, South Carolina

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Innovative Characterization of Multi-Component DNAPL in a Heterogeneous Aquifer

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Innovative Field Technique Used at NSCS Athens, Georgia

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The Integration of the Membrane Interface Probe with In-Situ Remediation Injection Technology to Facilitate Cost Effective Treatment of Groundwater

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Methodology for Integrating Direct Sensing Tools with In-Situ Remediation Injection Technology to Facilitate Effective Treatment of Groundwater

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Rapid Detection of Volatile Organic Compounds in the Subsurface by Membrane Introduction into a Direct Sampling Ion Trap Mass Spectrometer

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Real-Time DNAPL Source Delineation Using the Triad Approach

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Site Characterization with the Membrane Interface Probe

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Soil Screening Using the Membrane Interface Probe: Controlling False Positives and False Negatives

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Source Characterization of a DNAPL Site using Multiple Assessment Techniques

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