Progress Toward the Determination of Correct Classification Rates in Fire Debris Analysis II: Utilizing Soft Independent Modeling of Class Analogy (SIMCA)

A multistep classification scheme was used to detect and classify ignitable liquid residues in fire debris into the classes defined by the ASTM E1618‐10 standard method. The total ion spectra (TIS) of the samples were classified by soft independent modeling of class analogy (SIMCA) with cross‐validation and tested on fire debris. For detection of ignitable liquid residue, the true‐positive rate was 94.2% for cross‐validation and 79.1% for fire debris, with false‐positive rates of 5.1% and 8.9%, respectively. Evaluation of SIMCA classifications for fire debris relative to a reviewer's examination led to an increase in the true‐positive rate to 95.1%; however, the false‐positive rate also increased to 15.0%. The correct classification rates for assigning ignitable liquid residues into ASTM E1618‐10 classes were generally in the range of 80–90%, with the exception of gasoline samples, which were incorrectly classified as aromatic solvents following evaporative weathering in fire debris.     

The development of analytical and interpretational protocols to facilitate the provenance establishment of polycarbonate headlamp lens material

Despite the forensic significance of polycarbonate headlamp lenses, robust analytical protocols to facilitate their discrimination are scarce. In this study, laser ablation inductively coupled plasma mass spectrometry has been applied to the analysis of polycarbonate headlamp lenses with multivariate chemometrics techniques utilized to facilitate interpretation of the data. The analytical protocol involves the analysis of 46 analytes on material comprising the exterior surface of the lens. Using this data, it was found that although minor variation exists within a single headlamp lens, discrimination between lenses produced from a single manufacturing plant was still possible using iterative forward stepwise linear discriminant analysis processes. Discrimination between all headlamp lenses, with the exception of some lenses produced on the same day in a single plant, could be achieved using the analytical protocol. Furthermore, an interpretational protocol has been developed that has successfully classified all tested headlamp lens samples, within the discrimination limits of the analytical method.     

Association of Ignitable Liquid Residues to Neat Ignitable Liquids in the Presence of Matrix Interferences Using Chemometric Procedures*,†

Abstract: In fire debris analysis, weathering of ignitable liquids and matrix interferences can make the identification of ignitable liquid residues (ILRs) difficult. An objective method was developed to associate ILRs with the corresponding neat liquid with discrimination from matrix interferences using principal components analysis (PCA) and Pearson product moment correlation (PPMC) coefficients. Six ignitable liquids (gasoline, diesel, ultra pure paraffin lamp oil, adhesive remover, torch fuel, paint thinner) were spiked onto carpet, which was burned, then extracted using passive headspace extraction, and analyzed by gas chromatography‐mass spectrometry. Both light and heavy burn conditions were investigated. In the PCA scores plot, ignitable liquids were discriminated based on alkane and aromatic content. All ILRs were successfully associated with the corresponding neat liquid using both PCA and PPMC coefficients, regardless of the extent of burning. The method developed in this research may make the association of ILRs with corresponding neat liquids more objective.     

Establishing of chemical composition of printing ink

The subject of the examinations was primarily court tax marks of 50 and 200 PLN, which were suspected not to be genuine. Both inks on the questioned marks as well as comparative genuine marks and inks sent by the manufacturer were analyzed. No information about their chemical composition was available from manufacturer. In the examinations, infrared (IR), visible, X-ray fluorescence, and Raman spectrometry were used. The examinations showed that inks and glue on the marks of both values were the same as samples of those sent by the manufacturer. Discrepancies in some results were observed probably due to contamination, that is, an accidental presence of the foreign substance on the surface (e.g., sweat, saliva while sticking the marks to the surface or physical handling of the documents). It was concluded that there are original (genuine) court tax marks.     

微波消解ICP-MS法检测生物检材中汞元素

目的 建立生物检材中汞的电感耦合等离子体质谱分析方法.方法 采用微波消解法处理样品,以铟(115In)作内标,用电感耦合等离子体质谱仪对血液、尿液和头发中的汞含量进行分析.选择金与汞形成金汞齐,对金消除汞记忆效应的能力进行考察.结果 方法检出限为0.01μg/L,准确度为97.0%～107.1%.检测中添加金质量浓度在...