| Popis: |
Tougher security requirements and an increasing number of terror attacks have led to rapid advances in the field of explosive detection in the past few years. Detection systems have to be tested and validated with realistic samples and amounts as early as possible during the development. However, at present, well defined and homogeneous test materials which are a crucial requirement for development and validation of trace detection systems are not available. Existing preparation methods of reference samples, such as drop-and-dry (drop casting) methods, present a range of variability and reproducibility issues, including inhomogeneous sample coverage and material waste. Especially for the preparation of samples for optical stand-off technologies the drop-on-demand and inkjet printing technology could be a promising method of producing standardized chemically contaminated test materials with high accuracy, precision, scalability, and flexibility to allow for the inexpensive, high-throughput production. Test samples with contaminations ranging from nanogrammes to microgrammes have been prepared and analysed over several weeks of storage. The influence of plot parameters on the morphology and durability of printed samples of various common explosives have been investigated on different substrates. HPLC measurements were made to quantitatively evaluate the durability of printed samples. The morphology of the test samples was additionally characterized by optical microscopy and confocal Raman-microscopy. Besides the occurrence of polymorphic phase changes, described in literature for low concentrated drop-on-demand samples of RDX, we observed changes in sample distribution by recrystallization of some explosives in the printed samples. This paper focuses on the optimization of methods for the preparation of test samples and on the analysis especially concerning the effect of polymorphic phase changes caused by inkjet printing of samples. |
