GC-MS and HPTLC Analysis

GC-MS, the other part was dried until the solvent was completely removed and filled with distilled water in a volume of 0.5 ml for each swab for investigation by the IC method. The filters were dried and left for further research.

To detect trace amounts of high explosives, methanol swabs were examined using HPTLC and GC-MS methods.

HPTLC Study

The HPTLC study was carried out using a complex of chromatographic equipment from the Camag company (Switzerland) under the following conditions:

• "HPTLC Silica gel 60 F 254" plate from Merck (Germany);
• Volume of the applied sample - 40 μl;
• Eluent - benzene;
• Eluent rise height from the start line - 50 mm;
• Control sample - an acetone solution of the most well-known high explosives (TNT, hexogen, octogen, PETN, nitroglycerin, tetryl, and picric acid).

The presence of explosives was established by the correspondence of the relative mobility values of the substance spots on the chromatograms of the test and control solutions, as well as by the reaction to the effects of developing reagents: a solution of diphenylamine in an alcohol-acetone mixture followed by irradiation with UV light at a wavelength of 366 nm and a solution of ethylenediamine in acetone.

GC-MS Study

The GC-MS study was carried out on a GCQ spectrometer from Finnigan MAT (USA). Separation of substances was carried out in a helium flow at a speed of 50 cm/s on a DB-5MS column from J & W Scientific (USA) with a diameter of 0.25 mm, a stationary phase layer thickness of 0.25 μm, and a length of 10 m. The volume of the injected sample was 1 μl. Injector temperature - 200 °C. Splitless injector mode. Column temperature: isothermal 70 °C for 1 min, then programmed heating at a rate of 25 °C/min. Ion source temperature - 150 °C, interface - 250 °C.

Mass spectra of the separated substances were recorded in the chemical ionization mode with methane reagent gas in the negative ion mass range of 35-300 amu. Identification of explosives was carried out by comparing the retention times and mass spectra of the substances in the test samples and comparison samples.

Results

As a result of the conducted research, it was established:

• Trace amounts at the level of $10^{-6} - 10^{-7}$ g of cyclotrimethylenetrinitramine (hexogen) and 2,4,6-trinitrotoluene (TNT) - high explosives - were found in the swabs from the raincoat;
• Trace amounts at the level of $10^{-8} - 10^{-9}$ g of TNT were found in the swabs from the cloth bag.

Other high explosives (octogen, PETN, tetryl, trinitroglycerin, and picric acid) at the level of $10^{-9} - 10^{-11}$ g (detection limits for different substances by these analysis methods) were not found in the swabs.

As is known, TNT and hexogen are widely used for the manufacture of industrial mixed compositions, which may include ammonium nitrate (saltpeter) and aluminum in the form of powder or dust as components.