ABSTRACT
The application of high resolution magic angle spinning (HR-MAS) (1)H NMR spectroscopy is ideally suited for the differentiation of plastics. In addition to the actual material composition, the different types of polymer architectures and tacticity provide characteristic signals in the fingerprint of the (1)H NMR spectra. The method facilitates forensic comparison, as even small amounts of insoluble but swellable plastic particles are utilized. The performance of HR-MAS NMR can be verified against other methods that were recently addressed in various articles about forensic tape comparison. In this study samples of the 90 electrical tapes already referenced by the FBI laboratory were used. The discrimination power of HR-MAS is demonstrated by the fact that more tape groups can be distinguished by NMR spectroscopy than by using the combined evaluation of several commonly used analytical techniques. An additional advantage of this robust and quick method is the very simple sample preparation.
ABSTRACT
For many years now, Pabst's micro-press has been used in German forensic science laboratories as a valuable addition to methods of comparative analysis of plastic trace evidence. However, it is as yet hardly known in laboratories outside of Germany. The principal reproducibility is demonstrated by a homogeneity check of a raw backing material of defined origin. The illustrated results of a proficiency test emphasise the applicability of the Pabst method for forensic comparisons. The discrimination power of the Pabst method was tested by taking 90 black PVC-backings provided by the FBI Laboratory, i.e. those that could not be discriminated by standard methods. In this way further discriminations could be achieved. In the following, the Pabst method is therefore introduced as a straightforward, inexpensive and useful tool.
