Janina Zięba-Palus

Comparison of the Effectiveness of Tenax TA® and Carbotrap 300® in Concentration of Flammable Liquids Compounds

ABSTRACT: The aim of research was to compare two adsorbents, Tenax TA® and Carbotrap 300®, to evaluate their usefulness as passive adsorbents of flammable liquids compounds. It was also to determine whether Carbotrap 300® could be used in a passive adsorption mode, contrary to manufacturer recommendations. To compare the adsorption properties and the thermal desorption efficiency for Tenax TA® and Carbotrap, the components of test mixture were adsorbed and then chromatographically analyzed. The analysis was conducted by means of an automated thermal desorber coupled with a gas chromatograph and a mass spectrometer. This research established that although these adsorbents significantly differ from each other in adsorption properties, each of them can be successfully used for passive adsorption of ignitable liquids compounds. Tenax TA® turned out to be more effective for the adsorption of nonpolar, high‐boiling compounds, whereas Carbotrap is more effective for polar and volatile compounds. The examined adsorbents differ in their susceptibility to thermal desorption. For Carbotrap 300®, after the analysis an additional treatment is required to remove the remnants of adsorbed compounds. With Tenax TA®, this additional step is not necessary because the thermal desorption is sufficiently effective that this product is immediately ready for re‐use.

Application of Infrared and Raman Spectroscopy in Paint Trace Examination

Raman spectroscopy has proved to be a promising technique in forensic examinations, where optical microscopy, micro‐infrared spectroscopy, and microspectrophotometry in the visible and UV range are used for identification and differentiation between paint traces. Often no organic pigments are detected using Fourier transform infrared spectroscopy, because their content in a trace is usually undetectable. Application of a micro‐Raman spectrometer equipped with several excitation lasers helps forensic experts in paint analysis enabling identification of main pigments. Three cases concerning comparative examination of car paint are discussed in detail. The comparison of Raman spectra of paint chips found on clothing of a victim or smears found on body of a damaged car to these of paint chips originated from the suspected car enabled us to identify the car involved in the accident. When no comparative material is available, the method can be useful in establishing the color and make of the car.

Characterization of Blue Pigments Used in Automotive Paints by Raman Spectroscopy

Micro‐Raman spectroscopy was applied to forensic identification of pigments in paint chips and provided differentiation between paint samples. Sixty‐six blue automotive paint samples, 26 solid and 40 metallic were examined. It was found that the majority of the collected Raman spectra provided information about the pigments present. However, in some cases, fluorescence precluded pigment identification. Using laser excitation at longer wavelengths or pretreatment to effect photobleaching often resulted in reduced fluorescence, particularly for solid color samples, and allowed pigment identification. The examined samples were compared pairwise taking into account number, location, and intensity of absorption bands in their infrared spectra. The estimated discrimination power ranged from 97% for solid paint samples to 99% for metallic paint samples.

Differentiation of used motor oils on the basis of their IR spectra with application of cluster analysis

Abstract Two brands of motor oils, Elf and Castrol, were examined for criminalistic purposes. The aim was to distinguish between oil samples of varying degree of use. The chemical composition of the oils expressed by their infrared spectra was the basis of investigations. The mathematical approach applied to processing and interpretation of the physicochemical data was a chemometric procedure consisting of a few stages and including such methods as factor and cluster analysis. It was shown that the procedure presented can be recommended as very helpful for qualitative estimation of the effects examined.

Establishing of Chemical Composition of Printing Ink

Abstract:  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.

Information-theoretical comparison of likelihood ratio methods of forensic evidence evaluation

Forensic evidence in the form of two-level hierarchical multivariate continuous data is modelled using a likelihood ratio approach. Data are available from fragments of glass and of paint. Cross-entropy is used to compare the results with a neutral method and a method using the correct answers.

Comparative Analysis of Car Paint Traces in Terms of Color by VIS Microspectrometry for Forensic Needs

The usefulness of VIS microspectrometry for comparison of very small car paint traces was studied. Eighteen samples of solid and metallic paints taken from new and repainted cars were examined. Each sample was measured in both transmittance and reflectance mode (on top surface and on cross-section). Using the CIELAB units the repeatability of the color measurement was assessed. A criterion allowing two parts of the same sample and two samples of the same color to be distinguished was established. The method was proved to be an useful instrumental tool–complementary to other analytical methods (e.g., IR spectrometry)–in examination of car paint traces for forensic purposes.

Chemical analysis of post explosion samples obtained as a result of model field experiments

Five different explosives were detonated in a series of field experiments. Each experiment (detonation of the charge of each specific explosive) was repeated three times. The experiments were conducted under controlled conditions, exceeding those of research published so far. Detonated charges were uniform in size and, as far as possible, in shape. The explosives used originated from the same batch. Additionally, the same kind of electric detonators were used. Witness plates (sheets of galvanised steel 100 cm × 90 cm × 0.5 mm) were used to collect post-blast residues in a reproducible way. They were placed relatively close to the charge to minimise the influence of the wind. Samples were collected by systematic swabbing of the surface of the plate by acetone moistened cotton swabs. Samples were packed tight, transferred to the laboratory, and extracted with methanol. Extracts were concentrated by solvent evaporation, cleaned by centrifugation, and analysed using HPLC-DAD. Each extract was analysed three times and the mean value of the amount of the given explosive within the extract was calculated. For each of the explosive materials used the results of the repetition of the experiments proved them to be irreproducible. After each detonation of a specific charge different amounts of given explosives were found in post-blast samples. Also, the intuitively expected relationship between the distance from the charge and amount of post-blast residues were not observed. These results are consistent with previously published results of field experiments. The lack of reproducibility may be explained by differences in efficiency of detonation. The efficiency of a detonation may be influenced even by small differences in the shape of the charge as well as by the position and properties of the detonator. The lack of dependency between the amount of the explosive in the post-blast samples and the distance from the charge may be explained by the fact that during detonation, particles of unreacted explosives are not uniformly dispersed in all directions.

Chromatographic Analysis of Tire Rubber Samples as the Basis of Their Differentiation and Classification for Forensic Purposes

A pyrolysis gas chromatography-mass spectrometry (GC-MS) method was applied for the comparative analysis of 42 samples of rubber collected from passenger car tires. It was found that rubber samples originating from different tires can, in most cases, be effectively differentiated. The rubber samples were first assigned to one of three classes on the basis of the main components present in chromatograms (styrene and limonene). Then peaks obtained from trace constituents of the rubber were taken into account. In most cases, the differences between the analyzed samples were sufficient to distinguish them. In this study, an on-line derivatization technique (using tetramethylammonium hydroxide) was applied. In some cases, this technique made it possible to demonstrate differences that were invisible in normal analysis. The study showed that the pyrolysis GC-MS method was an effective tool to differentiate between samples of tire rubber. The estimated discrimination power without derivatization ranged from 90% (styrene-butadiene rubber based) to 100% (natural/styrene-butadiene rubber samples). Derivatization increased the former discrimination power to 99%.

Comparing the Color of Forensic Traces

Microspectrometry in the visible range is routinely applied in comparative examination of criminalistic traces such as paint chips, single fibers, and inks on questioned documents. It makes it possible to analyze a very small amount of sample and provides objective information about its color as well as helping to distinguish samples of similar colors. Measurements of Vis spectra are performed both in transmittance and reflectance mode, depending on the kind of traces. Application of the CIELab color system enables us to define color precisely and make use of color databases.