FORENSIC CHEMISTRY LABORATORY MANUAL

by R.Q. Thompson; Oberlin College

IDENTIFICATION OF ORGANIC EXPLOSIVES ON PLASTIC SURFACES

Objective

To identify the explosive used, if any, to cause a bomb blast at the crime scene.

 

Sample

Simulated bomb blast debris (plastic milk jug) containing trace amounts of organic explosives on its surface. Prepare the sample in the following way.

Place 20 drops of a mixture of explosives (0.25 – 2.0 µg/mL in acetonitrile) at random on one side of a plastic quart milk jug. Allow the acetonitrile to evaporate. Store the jug in a sealed plastic bag in the refrigerator until it will be processed.

 

Reagents

Standard solutions, 1000 µg/mL in acetonitrile (e.g. from Cerilliant), for eight of the most important organic high explosives: HMX, RDX, nitroglycerin, PETN, Tetryl, TNT, 2,4-dinitrotoluene, 2-nitrotoluene.

 

Standard Reference Material

 

None

 

Method

Solid phase extraction ; liquid chromatography

 

Special equipment

Liquid chromatograph with C18 column and diode array detector ; 3-mL, polymeric reverse phase, solid phase extraction (SPE) cartridges (e.g. Oasis from Waters) ; vacuum manifold for SPE ; solvent evaporation system (heating block and a source of nitrogen); 2-mL chromatography vials with screw caps

 

Procedure

For instructor (detailed); For student (brief)

 

Typical results

Chromatograms of explosives standards and sample: 50 µL injection of liquid sample; C18 column; isocratic elution with 50:45:5 water:methanol:acetonitrile, flowing at 0.8 mL/min. UV spectra of RDX, Tetryl, and TNT. Typical results and discussion.