Nitro knowledge: Ethylene glycol dinitrate measured in plastic explosives

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  • Published: Feb 6, 2012
  • Author: Steve Down
  • Channels: HPLC
thumbnail image: Nitro knowledge: Ethylene glycol dinitrate measured in plastic explosives


Dynamite after Nobel

The term dynamite is often applied to several types of explosive based on nitro-containing compounds but the original one was invented by Alfred Nobel and was based on nitroglycerin with diatomaceous earth as an absorbent filler. Several modifications have been introduced over the years in which ammonium nitrate and sodium nitrate were added as explosives and sawdust, crushed shells and wood pulp have been used as fillers.

Nowadays, another nitro compound, ethylene glycol dinitrate (EGDN), is often used to partially or completely replace the nitroglycerin to create a more stable product, due to its superior knock resistance. It also lowers the freezing point of nitroglycerin, so that the explosive can be used in industrial applications in cold climates.

One such explosive is Goma-2 ECO, produced in Spain for mining and demolition purposes and for use by the military. It has also found its way into the inventory of various terrorist organisations and has been implicated in atrocities like the Madrid train bombings in 2004.

Goma-2 ECO is based on nitrocellulose, ammonium nitrate, and 25-30% EGDN as well as a filler of flour or sawdust and some minor components. An earlier version of this explosive designated GOMA-2 EC also contained dinitrotoluene as a further active component.

Distinguishing between the different types of nitro-containing explosives can be tricky but a team of researchers in Madrid noted the absence of an analytical method for measuring EGDN in dynamites. This would be useful for forensic and industrial quality control applications, so they developed a procedure based on HPLC which was described in the Journal of Separation Science.


Explosive EGDN measured by HPLC

Carmen Garcia-Ruiz and co-researchers from the University of Alcala, Alcala de Henares, and the Criminalistic Service of the Civil Guard decided to implement a novel extraction procedure that removed all of the components from the dynamite matrix, due to the heterogeneous nature of the material.

They mixed the explosive with water to produce an aqueous extract before mixing the residual matter with methanol to give a second extract. In this way, nitrocellulose, EGDN and all of the salts were extracted and only sawdust remained. A single extraction with a mixture of water and methanol did not achieve total dissolution, so the two-step procedure was required. Nevertheless, it was far less complicated and quicker than one published method in which ten steps were necessary for total recovery of the nitro compounds.

Each of the two extracts was analysed for EGDN by HPLC using an octadecylsilica column with increasing concentrations of methanol in water over the elution period, followed by UV detection at 230 nm. Under these conditions, analysis of a standard solution of several nitro compounds that might be present in different explosives showed that they were eluted separately. They included EGDN, nitroglycerin, TNT, and several dintrotoluenes.

The detection and quantitation limits of EGDN were acceptable at 1.7 and 5.6 mg/L, respectively, and the recoveries were in the range 101-106% for low-to-high levels of the compound. The other analytical data such as precision, accuracy and repeatability had acceptable values.

The method was applied to a commercial sample of Goma-2 ECO to determine that the EGDN content was 30.29%. This was within the declared range of 25.7-31.4% specified by the manufacturer, indicating the applicability of the procedure.

The HPLC method incorporating the enhanced extraction procedure should be useful for the routine quality control of commercial explosives containing EGDN, as well as forensic applications to determine the identity of seized explosives and, possibly, the blast residues after terrorist attacks.



The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

  

The explosive component ethylene glycol dinitrate has been measured for the first time in Goma-2 ECO, an industrial type of dynamite, which has also been deployed by terrorists

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