Combining grazing incidence X-rays and micro-diffraction for qualitative phase identification in forensic powdered micro-samples.

Capillary diffraction or microdiffraction are standard techniques for characterizing small samples when only a few milligrams are available. On the other hand, we have typical grazing incidence diffraction or different variations of grazing incidence (GI) diffraction used, such as in-plane grazing incidence (IP-GI) or GI using a micro focusing source, to study thin films. However, when few powder micrograms are available, the characterization task is complicated. In the present work, few micrograms of typical forensic samples are analyzed using standard Bragg-Brentano, X-ray powder diffraction geometry, and grazing incidence X-ray micro-diffraction (GIµXRD). Samples include soils, cosmetic eyeshadows, two different pyrotechnic materials, and a highly explosive mixture contained at primer cup of ammunition. The analysis was carried out from 1 to 5 degrees of the incident parallel beam with a shaking sample. Depending on the fixed incident angle, different small regions of the diffraction patterns showed an improvement in the intensity of the peaks with respect to the conventional Bragg-Brentano configuration. However, 3-5 degrees of the fixed incident beam showed the best results. This new data acquisition technique, based on the combination of two known diffraction methods, could be a powerful tool for studying samples outside of forensic sciences such as nanomaterials, medicine, or any other field where the sample quantity is extremely small, also, without the need to transport evidence and travel to external facilities with higher analytical performance such as synchrotron radiation installations or other large experimental facilities.