Cooperative Study on Confocal Micro-XRF for low Z elements in forensic applications

The mixing of illegal drugs in food is becoming a problem in Japan as well as internationally. A fast detection system would help to identify the drugs. We propose confocal micro X-ray fluorescence analysis (XRF) as a promising new method after speciation using Thin Layer Chromatography (TLC). In comparison to other analytical methods as ICP-MS it would be faster and with less instrumental effort and can be used for screening. The 2 drugs under consideration for present target are Bromovalerylurea (bromisoval) and Fenitrothion. Specific elements have to be determined in specific compounds. Br in the first and P and S in the second will give useful information to specify the chemicals. For this application confocal micro XRF has to be extended to the detection of low Z elements. Several requirements are necessary: measurements have to be performed under vacuum conditions, excitation conditions have to be optimized to excite light elements efficiently and a special detector suitable for the detection of low energy fluorescence radiation is necessary. The aims of the project are: vacuum chamber for confocal micro-XRF setup, with the possibility to adjust under vacuum conditions. evaluation the performance of the new developed system with standard samples. Determination of detection limits and special resolution evaluation of quantification models specially for low Z elements application in the field of forensic science to the detection of drugs after TLC to reduce scattering in air and absorption in air to determine Phosphor and Sulphur. testing the ability of the developed system for fast screening. The project should join the capacities of the Austrian and the Japanese research groups to the described application. The Austrian group has long term experience in the development of instruments to perform EDXRF measurements of light elements. The Japanese group of Prof. Tsuji has expertise in confocal micro XRF using X-ray tubes and improving their performance. A synergy of both expertise`s is the main goal of the project including the exchange of knowledge of young scientists.

Micro X-ray fluorescence (micro-XRF) is an analytical method to determine the spatial distribution of major, minor and trace elements in a sample on the micrometer scale. Confocal micro-XRF extends the technique to allow for three dimensional analyses thereby greatly increasing the versatility of the method. While the technique is well established on synchrotron radiation sources, spectrometers in the laboratory are not used routinely. In order to improve laboratory spectrometers a joint research project has been carried out comparing a spectrometer for light element analysis installed at the Atominstitut in Vienna (ATI) and a high spatial resolution spectrometer at Osaka City University in Japan (OCU). In the course of this program an improved spectrometer combining advantages of both systems has been designed and installed at OCU, using insights gained by both research groups. Comparing results of three spectrometers improved our understanding of confocal micro-XRF and showed that both features, high spatial resolution and a wide elemental range, are important and can be achieved.XRF based methods are ideally suited for forensic elemental analysis as they are non-destructive, require little sample preparation and offer simultaneous multi element detection when using an energy dispersive detector. Applications in other fields like cultural heritage have often the same requirements making this a very versatile technique. Analysing forensic samples with the different spectrometers showed the improvements that were achieved with the new setup at OCU and that the analysis of forensic samples with this method is feasible. 3D analysis allows for the depth profiling of a sample on the micrometer scale. This is an important feature to analyse e.g. chipped car paint in order to determine their origin. However, interpreting acquired data can be difficult. In order to improve our understanding a simulation model was developed and tested. Parameter studies with this model also showed the capabilities and limitations of the current setup at ATI and how to improve the system in the future. It will also help to develop quantification models for micro-XRF.The joint research project improved the understanding of confocal micro-XRF for both research groups, besides the extensive exchange of knowledge between Japanese and Austrian young scientists. We compared the experimental setups using real world samples and reference materials and were able to improve the analytical capabilities with a new setup at OCU. A new simulation model improved the understanding of non-destructive depth profiling using confocal micro-XRF.