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Assessment of the Utility of X-ray Fluorescence for the Chemical Characterization and Comparison of Black Electrical Tape Backings

NCJ Number
Forensic Chemistry Volume: 13 Dated: May 2019
Date Published
May 2019
6 pages
This study used X-ray Fluorescence (XRF) in the chemical characterization and comparison of black electrical tape backings and compared the utility of this process to previously published SEM-EDS and LA-ICP-MS data.

Elemental analysis of electrical tapes is typically conducted by Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS), although Laser Ablation-Inductively Coupled Plasma - Mass Spectrometry (LA-ICP-MS) was recently shown to improve the sensitivity of the determinations. In the current study, three XRF systems were used to evaluate a range of configurations commonly available at crime laboratories. A set of 40 electrical tape backings known to originate from different sources were used to assess the inter-roll variability, discrimination, and classification capabilities of the method. The discrimination for this tape set increased from 78.8 percent achieved by SEM-EDS to 81.5-91.0 percent by XRF, depending on the instrumental configuration. In comparison, LA-ICP-MS achieved 84.6 percent discrimination on these tapes. The overall characterization, classification, and discrimination capabilities for this set improved as follows: SEM-EDS<iXRF<small spot size benchtop XRF with SDD, LA-ICP-MS<large spot size XRF. A set of 20 pieces of tapes collected from the same roll were analyzed for intra-roll variability. Duplicate control same-source samples were used to evaluate inter-day and intra-day instrument variability. No false exclusions were observed in the data set, demonstrating the within-sample variability and instrumental variability are relatively lower than the inter-sample variability. One concern of the method is the penetration depth of the X-ray beam beyond the target backing, requiring careful sample preparation to avoid interference from the adhesive or sample holder. XRF is a viable analytical tool for the forensic examination of electrical tapes, with advantages of speed of analysis, minimal destruction of the tape, and high informing power. (publisher abstract modified)

Date Published: May 1, 2019