March 8, 2011

Headspace Monitoring

The following are opinions and recommendations. Please consult your site’s or company’s procedures and specifications for more information.

The use of portable PhotoIonization Detectors and Flame Ionization Detectors allows for important and costly decisions to be made quickly and intelligently during any site investigation. However, there are three important points to consider before any decision is made. 1.) Ensure you are using the correct instrument, 2.) Understand the limitations of that instrument, and 3.) Make sure you are using reliable and consistent methodology.

Headspace monitoring is the best field-ready method for determining the presence (and/or absence) of volatile and some semi-volatile organic compounds in soil and water samples.

• Half-fill two clean glass jars with the sample to be monitored. Immediately cover each jar with aluminum foil and tightly screw on the lid. Plastic bags should not be used due the possibility of VOCs in the plastic and openings.

• Allow approximately 10 minutes for headspace development. Samples should be stored in a heated area during development. Samples should also be shaken prior to storage and again prior to monitoring.

• When ready, visually check the headspace area for condensation. Moisture will have an effect on the performance of a PID. Even a small amount of moisture can contaminate a PID’s ion chamber making all subsequent readings drift.

• Upon removing the lid, immediately puncture the foil with the probe tip of the PID or FID and insert the end to the middle of the headspace. Take care to not touch the soil or water with the probe tip.

• Record the highest reading (the peak) displayed for both jars. This should occur within 5 seconds. Compare the values from each jar. Peak values should be consistent within 20% of each other.

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