Question

How is ion profiling useful in the identification of classes of ignitable liquids? Ions 117,118, 131, 132 are typical of which chemical class of compounds? What ASTM class of ignitable liquids contain these compounds?

Forensics question. Thanks!!

Answer 1

The mass spectra calculated by summing the intensities of each nominal mass over all chromatographic times, the summed ion spectra, were calculated for a set of 440 commercially available ignitable liquids that had been analyzed by gas chromatography–mass spectrometry. Each ignitable liquid is generally comprised of a mixture of chemicals, and the mixtures may be very complex in some cases, e.g., petroleum distillates, gasoline, etc. The summed ion spectra were evaluated to determine if they contained sufficient information content to allow their use for rapid and accurate identification of the ignitable liquid in a database or library. The summed ion nominal mass spectra were encoded in one bit per channel at 1% transition intensity and a set of 96,580 unique pairwise comparisons were made between spectra, resulting in an average of approximately 50 differing channels per comparison. A subset of 62 summed ion spectra were further compared by a similarity metric and found by cluster analysis to group closely along the ASTM ignitable liquid classification scheme. Receiver operator characteristic analysis of the use of the similarity index in combination with the summed ion spectra was shown to provide 99% probability of correct liquid identification and 95% probability of correct ASTM classification by primary and sub-class. Interlaboratory tests found 95% probability of correct liquid identification and 85% probability of correct ASTM classification at the primary class level. These results demonstrate the use of the summed ion spectrum as a first step in the rapid identification of an ignitable liquid by database or library searching.

Hence to know the nature of these chemical compounds and their reactions, chemistry formulas plays a vital role.For example: NaCl which consists of Na⁺ (metalion) and Cl^– (non-metal ion) .117, Hydrocyanic acid formula, HCN .131, Iodic acid formula, HIO3.132, Iodide formula, I2.

The application of comprehensive two-dimensional gas chromatography (GC × GC) for the forensic analysis of ignitable liquids in fire debris is reported. GC × GC is a high resolution, multidimensional gas chromatographic method in which each component of a complex mixture is subjected to two independent chromatographic separations.GC × GC chromatograms were used to identify and classify ignitable liquids, detect minor differences between similar ignitable liquids, track the chemical changes associated with weathering, characterize the chemical composition of fire debris pyrolysates, and detect weathered ignitable liquids against a background of fire debris pyrolysates.