This paper ('Influence of soil type on chemiresistive detection of buried ANFO' published in Forensic Chemistry) by Dr Merel J. Lefferts and Professor Martin Castell, demonstrates the influence of soil type on the chemiresistive detection of ammonium nitrate/fuel oil (ANFO), one of the most commonly used materials for improvised explosive devices (IEDs).
Concealment is one of the main challenges of IED detection and increases the need for highly sensitive vapour sensors. Conducting polymer based chemiresistive sensors offer a potential solution because they are small, easy to use, relatively inexpensive and can operate at room temperature. This paper reports on percolation networks of polypyrrole which are used to detect ANFO buried under various types of soil.
Reliable detection of ANFO buried under layers of sand or sandy soil is demonstrated at sub-ppm concentrations, however clay is found to act as a significant barrier to the permeability of the analyte vapour.