Assessing the expanded capacity of modern μ-XRF SDD systems for forensic analysis through an interlaboratory study: Part I—Electrical tapes

Recent modernization of micro-X-ray Fluorescence Spectrometry (μ-XRF) instrumentation has increased capabilities for elemental analysis in forensic casework. In this study, the analytical performance of several μ-XRF instrument configurations, each equipped with silicon drift detectors (SDDs), is assessed through an interlaboratory study (ILS) using two novel poly(vinyl chloride) (PVC) matrix-matched standards (de Bruin-Hoegée et al., 2023 [1]). Also, the informative value of μ-XRF in casework-like electrical tape samples is evaluated, and a quantitative metric known as spectral contrast angle ratio (SCAR) for spectral data interpretation is mathematically normalized. The ILS evaluates inter-instrumental and inter-examiner variability in comparing and interpreting spectral data. The ILS exercise consists of ten sets of electrical tapes from various ground truth sources (same roll, same package, different rolls), each with five sections per set. Data is collected across eight laboratories, with 11 instrumental configurations. Results from spectral overlay and SCAR pairwise comparisons (45 each) are compared between each laboratory and each set of instrumental parameters (495 comparison pairs, 15 replicates per sample). The results of this study reinforce the utility of μ-XRF in tape examinations and indicate strong inter-laboratory agreement, with low false-inclusion and exclusion rates (<2.4 % and < 4.6 %, respectively). The study demonstrates the benefits of comparing SCAR metrics across laboratories. The observed trends in detection capabilities across different instrumental configurations can help identify relevant parameters for consistent analysis and interpretation across different laboratories and future methodology implementation in forensic casework. Ultimately, standardized interpretation adds value to the tape evidence to further substantiate conclusions during investigative stages and in the courtroom.