Soil samples for volatile organic compound (VOC) analysis are usually shipped to the laboratory cooled by ice packs in coolers (approximately 4 °C). Both EPA and ASTM recognize that freezing is better for preserving VOCs. But how do you field-freeze samples and keep them frozen during shipping?
Power-operated freezer compartments are not feasible for field use. Dry ice? Dry ice is a regulated substance that sublimes to gaseous carbon dioxide, which displaces air in sealed aircraft. What’s more, at -78 °C, dry ice can damage the seals on sample containers, causing VOCs to be lost as samples thaw.
WRI’s Integrated Freezer System uses a frozen phase change liquid (PCL) solution in specially modified coolers to maintain freezer temperatures. Unlike conventional storage materials, when frozen PCL changes from solid to liquid, it continues to absorb heat without a significant rise in temperature. Phase change liquids can store 5 to 14 times more heat per unit volume than conventional storage materials such as water.
The EPA’s specified holding time for storing soil samples in airtight coring devices preserved by freezing is 48 hours. WRI is optimizing all variables―PCL, bag size, bag and sample arrangement, and cooler insulation―to achieve <-7 to -20 ºC storage for 48 hours. Continued testing will keep the Integrated Freezer System on the fast path to becoming the first commercial-ready system for freeze-shipping soil samples.
WRI’s Integrated Freezer System advances NETL NPTO Effective Environmental Protection Research for technologies and practices that promote environmental protection and compliance. In addition, this state-of-the-art system will have applications, such as medical and food preservation, that extend far beyond environmental sample shipping.