Covariance Mapping in the Analysis of Ignitable Liquids by Gas Chromatography/Mass Spectrometry

Abstract

The covariance matrix computed from the retention time-ion abundance data matrix from gas chromatography/mass spectrometry analysis of ignitable liquids is shown to be a useful tool for automated identification of ignitable liquids in a database. The absolute value of the element-by-element difference between two normalized covariance matrices is shown to quantitatively differentiate between ignitable liquids composed of complex mixtures of hydrocarbons and is amenable to automated searching of ignitable liquid databases. The covariance mapping method is applied to a matrix-contaminated postburn sample, allowing the determination of a high degree of similarity between the ignitable liquid and a heavily evaporated gasoline.

Application of an HS–MS for the detection of ignitable liquids from fire debris

“…There are several ways to achieve this goal, including solid phase microextraction [11], static headspace adsorption with Tenax [12] or headspace sorptive extraction [5] to name but a few. However, passive headspace concentration with activated charcoal strips (ACSs) is currently the most commonly used method to isolate ILRs from fire debris because of its sensitivity, ease of use, and its non-destructive nature [13,14]. Besides, activated charcoal is an excellent nonpolar adsorbent for the collection and retention of C6-C20 hydrocarbons so it is an ideal material for petroleum-based products [15].…”

“…For this reason, some authors have proposed alternative methods to TIC. Sigman et al developed a covariance mapping method to group ignitable liquids belonging to the same ASTM classification while retaining some of the chromatographic information, which is encoded in covariance of the different ions [14,18]. This method allowed the grouping similar ignitable liquids but it was computationally demanding when implemented as a database search application.…”

Class-conditional feature modeling for ignitable liquid classification with substantial substrate contribution in fire debris analysis

“…The GC-MS data was then used, following the procedure described by Sigman et al [20,21] to derive total ion spectra (TIS). Briefly, this is the procedure by which the 2nd order chromatographic data is collapsed along the retention time dimension, yielding a profile of relative ion abundances in the total sample.…”

Fire investigation and ignitable liquid residue analysis—A review: 2001–2007

“…Multiple regression coefficients were calculated for different samples of unevaporated and evaporated gasoline to determine, first, if the sample was a gasoline and, second, to discriminate between samples of gasoline [293]. The use of covariance mapping of GC-MS data was used to compare samples of neat ignitable liquids in the absence of background interferences [294]. Covariance mapping was used to discriminate a set of 10 unevaporated gasoline samples; however, the effects of evaporation on the mapping technique were not addressed in the article [295].…”