Signal-to-noise ratios in forensic glass analysis by micro X-ray fluorescence spectrometry

Micro X-ray fluorescence (-XRF) spectrometry using an energy dispersive X-ray (EDS) detector is capable of detecting certain major, minor, and trace elements that permit potential discrimination of glass fragments in forensic cases on the basis of differences in elemental composition. Often, elements used for discrimination are present at concentrations near the detection limit of the EDS system, and the decision whether to utilize these minor peaks in a comparative analysis has generally been left to the discretion of the examiner. The use of signal-to-noise ratios (SNRs) of spectral peaks provides additional objectivity in peak identification/label decisions and in the selection of elements in semiquantitative ratio comparisons. In addition, the use of SNRs enables calculations of limits of detection and limits of quantitation and the monitoring of instrument performance, and facilitates performance comparisons of different -XRF configurations. This paper demonstrates a practical method for applying the concepts of SNR, limits of detection, and limits of quantitation to -XRF generated EDS-based spectra, discusses the implications of such determinations, addresses spectral features that must be considered when making the calculations, and illustrates the application of these concepts to the example of forensic examination and comparison of glass samples. Copyright (c) 2012 John Wiley & Sons, Ltd.