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There is a new method to determine the chemical composition of liquids seized by police and suspected to be explosive.

Each year police forces seize tons of pyrotechnic substances which, in principle, are for indoor firework manufacturing (i.e. flares or those used in artistic or sporting events), but which also may end up in the hands of the wrong people.

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A group of chemists from the University of the Basque Country (UPV/EHU, Spain) developed a method that offers judges conclusive scientific tests on the nature of these liquids. Until now, resources went into detecting high explosives such as TNT, but very few for less powerful ones which can also be dangerous.

“We have found a relatively simple way to detect explosive or flammable compounds in suspicious liquids, by combining four techniques commonly used in laboratories,” said Kepa Castro, UPV/EHU researcher and the study’s lead author.

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On one hand, researchers can obtain the molecular composition of the substances using two spectroscopy techniques (Raman and infrared) with mobile devices in airports, customs or ports offices.

On the other hand, energy-dispersive spectroscopy (EDS) combined with scanning electron microscopy (SEM) images can determine which elements are in the sample.

“With the SEM-EDS technique we are able to observe how the sample’s elements are distributed and grouped (for example, calcium with sulphur suggests that calcium sulphate is present)” said Castro, “and by crossing data from four different techniques, we are able to check and confirm the results.”

To check the method, the scientists applied it to five seized liquid samples. Four of the samples presented substances used in indoor fireworks. Alcohols, such as isopropyl and methanol, used to dissolve compounds and the scientists managed to produce colored flames with them.

The team was surprised to find methanol used as a main solvent, given this compound is very toxic for human beings, causing acidosis and blindness, and some countries actually restrict it.

Boric acid was also in one of the other sample liquids. This substance is now on the list of Substances of Very High Concern (SVHC) as part of the European Union’s REACH Regulation (Registration, Evaluation, Authorization and Restriction of Chemical substances). These acids can have a negative effect on the human reproduction system.

No flammable or explosive substances were in the fifth sample. “It is probably a flame retardant, which is precisely used in fire prevention,” the researcher said.

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