Micro x-ray fluorescence spectroscopy (u-XRF) is a standard technique used for the elemental analysis of glass fragments in forensic casework. The glass specimens encountered in casework are usually small (< 1 mm), thin, irregularly-shaped fragments that are partially transparent to the exciting x-ray beam. Typically, the fragments are mounted on a thin plastic film and raised on an XRF sample cup (~≤ 3 cm in height) to reduce scatter from the stage. However, at these heights, there may still be significant stage scatter, which adversely affects the signal-to-background ratio (SBR) and the limit of detection (LOD). A plastic mount was designed and 3D-printed in-house to allow fragments to be raised as high as possible from the sample stage, thereby minimizing stage scatter. A small fragment (< 1 mm) of Standard Reference Material (SRM) 1831 was analyzed using the 3D-printed mount, using an XRF sample cup, and using no mount (i.e., directly on the stage). Most elements detected in glass showed an improvement in the SBR (and LOD) when using the 3D-printed mount for analyses. The greatest improvement (> 10%) was observed for lower atomic number elements (Na, Mg) and higher atomic number elements (Sr, Zr). Another simple method to improve SBR and LOD is through the use of filters. A small SRM 1831 glass fragment was analyzed using no filter and using various primary beam filters. Elements in the mid-energy range (Ti, Mn, Fe) showed the greatest improvement (> 20%) when using filters during analyses.
Forensic Science International
x-ray fluorescence, glass, forensics, signal-to-background ratio