Paper AS-ThP8
Investigation on Human Evidences using ToF-SIMS Combined with Advanced Matching Recognition

Thursday, October 25, 2018, 6:00 pm, Room Hall B

The expansion of the use of forensic sciences requires to develop new techniques providing prompt and reliable information. In terms of chemical analysis, the useful information ranges from trace elements, e.g. the elemental detection of residues in a specimen, to molecular information, e.g. the identification of high mass molecules. Time-of-Flight Secondary Ion Mass Spectrometry is able to provide a detailed 3D view of the elemental and molecular composition of solid samples and has already been used previously to analyze inorganic, organic and biological specimens, showing its strong potential to retrieve more information from trace evidence than the traditional methods.

Several challenges still prevent a widespread application of ToF-SIMS to forensic analysis. Samples from the human body are the most commonly collected specimens and these samples are particularly challenging for analysis due to the variety of specimens, including hair, fingerprints, fingernails and lipstick, and the complexity of the samples that can contain blood, saliva and/or sweat. A common material to almost all of the human specimens is cosmetics, which can provide crucial information about an individual. Through analysis of five different types of cosmetics - hair styling products, lipstick, lotion, nail polish, and foundations, we have collected a large range of ToF-SIMS spectra and build a cosmetic database from these reference samples.

The characterization of different types of human evidences has been performed to illustrate the large range of the possibilities given by the ToF-SIMS. However, to identify the chemical composition of the cosmetic residues and to determine their origins, advanced methods of classification and discrimination need to be applied. For example using Principal Component Analysis, it was possible to identify the cosmetic residues present on hair cuticles and to discriminate the hair product applied from a list of 16 references. Nevertheless, quantitative analysis can be required for identifying the exact nature of the residues. Thus, a new method combining Matching Factor and decision tree has been developed. Fingerprint analysis has been performed to identify the traces of residues contained in the fingerprint, which have also highlighted the fingerprint’s ridges. After PCA segmentation, the extracted mass spectrum from the residue’s region has been evaluated using a new matching recognition method, which has clearly indicated the origin of the cosmetic product.