Synthesis and characterisation of homemade urea nitrate explosive from commercial sources of urea

Abstract

The aim of this study was to investigate the preparation of urea nitrate (UN) using a range of urea sources followed by characterisationwithanalytical techniques routine to explosive analysis. The UN was prepared from lab grade urea, fertiliser urea, urea cold packs, diesel exhaust fluid (DEF) and Osmocote plant feed, resultingin six samples of UN as the Osmocote plant feed produced a blue and yellow product due to variation between products purchased at different times. Infrared and Raman spectroscopy revealed no notable differences between the samples apart from the blue UN product, which hada distinct peak in the IR spectra at 1150 cm−1. The Osmocote products couldbe discriminated by scanning electron microscopy energy-dispersive x-ray spectroscopy (SEM-EDS) and ion chromatography (IC), as bulk samples contained a range of trace metals and ions. Analysis by inductively coupled plasma mass spectrometry (ICP-MS)found 9 elementspresent at varying concentrations throughout the samples. The Osmocote products could be identified by the concentration of manganese, copper, and molybdenum whiletheDEF product could be discriminatedas it contained a high concentration of nickel compared to other samples. ICP-MS has potential to further discriminate between the lab grade, fertiliser and cold pack samples, however, additional statistical and chemometric analysis is necessary. This study highlights that seized UN can be identified as being prepared from DEF or an Osmocote product, and contributes to the forensic intelligence of improvised explosives by reporting how UN can be commercially sourced, prepared and characterised.