Chia Poh Ling*, Lim Chin Chin, Yap T.W, Michael Tay Ming Kiong
3rd EAFS, abstract no. FEX-FO-06 (oral presentation)
In the analysis of arson samples, analysts look for the presence of a series of alkanes, or certain profiles of aromatics peaks as the indication that the sample may contain possible ignitable liquid. Identification is based on the classification standard ASTM 1387 for gas chromatography and ASTM 1618 for gas chromatography/Mass Spectrometry.
In the interpretation of the laboratory analysis results, analysts have to be cautious about the possibility of interference products.
There are basically two types of interference products. The first type is from actual liquid petroleum products originally present in the substrate material. One good example is the kerosene fraction that is present in the ink used in the printing of certain newspaper. Subsequent analysis of the newspaper will show up the presence of an alkane profile consistent with that of kerosene. Common items that have this background interference include shoes, a variety of household products (insecticide, sprays, furniture, plastic products) and many types of paper products. The second type of interference “is due to the emission of pyrolysis products when the material is heated up. This second type of interference is easily recognizable and shall not be discussed here.
Very often, clothings of suspected arsonists are sent in to forensic laboratories to determine whether the clothings have been stained with any ignitable liquid, thus shedding some light on the history of the wearer. In Lentini et aI’s (J. Forensic Sci 2000; 45(5): 968-989) paper, he found that some fabrics have been observed to produce series of alkanes or alkylbenzenes. However, the authors contented that the profiles observed for alkylbenzenes are not complete for an identification of gasoline. With the advance of technology which had continuously lowered the instrumental detection limit, there comes a point whereby we are faced with the question of whether the profiles we had observed was due to that particular clothing being stained with ignitable liquid, or that the particular piece of clothing had a strong interference background due to the materials used.
This study surveys a wide variety of clothing/fabric to determine the type and concentration of the alkanes and/or aromatics peaks that are present. Samples were heated at 80°C for 16 hours in the oven and sampling was done by passive headspace concentration (ASTM 1412). Analysis was carried out using gas chromatographic/mass spectrometric (GC/MS) technique as described in ASTM 1618. Both the total ion chromatograms and extracted ion chromatograms/summed ion chromatograms were used to look for the presence of alkanes and aromatics peaks. It has been observed in our study that many types of clothing displayed full profiles of aromatic peaks that could be misinterpreted as gasoline.
The second part of this study looks at the persistence of ignitable liquid on clothing and the effects of washing on the analysis. Different types of fabrics (with and without background interference) were stained with different amount of ignitable liquid. These fabrics were then subjected to different treatments (air-dried, soaked in water, washed with detergent). The samples were then analysed for the presence of ignitable liquid. From this study, we hope to surface the problem of background interference in clothing and how that may complicate the forensic investigation of a suspected arsonist.