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Trejos T.,Florida International University | Becker S.,Forensic Science Institute | Berman T.,Orlando Regional Operations Center | Duecking M.,Forensic Science Institute | And 12 more authors.
Analytical and Bioanalytical Chemistry | Year: 2013

Elemental analysis of glass was conducted by 16 forensic science laboratories, providing a direct comparison between three analytical methods [micro-x-ray fluorescence spectroscopy (μ-XRF), solution analysis using inductively coupled plasma mass spectrometry (ICP-MS), and laser ablation inductively coupled plasma mass spectrometry]. Interlaboratory studies using glass standard reference materials and other glass samples were designed to (a) evaluate the analytical performance between different laboratories using the same method, (b) evaluate the analytical performance of the different methods, (c) evaluate the capabilities of the methods to correctly associate glass that originated from the same source and to correctly discriminate glass samples that do not share the same source, and (d) standardize the methods of analysis and interpretation of results. Reference materials NIST 612, NIST 1831, FGS 1, and FGS 2 were employed to cross-validate these sensitive techniques and to optimize and standardize the analytical protocols. The resulting figures of merit for the ICP-MS methods include repeatability better than 5 % RSD, reproducibility between laboratories better than 10 % RSD, bias better than 10 %, and limits of detection between 0.03 and 9 μg g-1 for the majority of the elements monitored. The figures of merit for the μ-XRF methods include repeatability better than 11 % RSD, reproducibility between laboratories after normalization of the data better than 16 % RSD, and limits of detection between 5.8 and 7,400 μg g-1. The results from this study also compare the analytical performance of different forensic science laboratories conducting elemental analysis of glass evidence fragments using the three analytical methods. [Figure not available: see fulltext.] © 2013 Springer-Verlag Berlin Heidelberg. Source


Ernst T.,Trace Evidence Unit | Berman T.,Orlando Regional Operations Center | Eckert-Lumsdon T.,U.S. Army | Olsson K.,Johnson County Crime Laboratory | And 5 more authors.
X-Ray Spectrometry | Year: 2014

Micro X-ray fluorescence (μ-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 μ-XRF configurations. This paper demonstrates a practical method for applying the concepts of SNR, limits of detection, and limits of quantitation to μ-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. © 2012 John Wiley & Sons, Ltd. Source


Trejos T.,Florida International University | Weis P.,Forensic Science Institute | Becker S.,Forensic Science Institute | Berman T.,Orlando Regional Operations Center | And 16 more authors.
Journal of Analytical Atomic Spectrometry | Year: 2013

Four interlaboratory tests were designed to evaluate the performance of match criteria for forensic comparisons of elemental composition of glass by μ-XRF, solution nebulization SN-ICP-MS, LA-ICP-OES and LA-ICP-MS. A total of 24 analysts in 18 laboratories participated in the tests. Glass specimens were selected to study the capabilities of the techniques to discriminate glass produced in the same manufacturing plant at different time intervals and to associate samples that originated from a single source. The assessment of the effectiveness of several match criteria included: confidence interval (±6s, ±5s, ±4s, ±3s, ±2s), modified confidence interval, t-test, range overlap, and Hotelling's T2. Error rates are reported for each of these criteria. Recommended match criteria were those found to produce the lowest combinations of type 1 and type 2 error rates. Performance of the studied match criteria was dependent on the homogeneity of the glass sources, the repeatability between analytical measurements, and the number of elements that were measured. The best results for μ-XRF data were obtained using spectral overlay followed by a ±3s confidence interval or range overlap. For ICP-based measurements, a wider match criterion, such as a modified confidence interval based on a fixed minimum relative standard deviation (±4s, >3-5% RSD), is recommended due to the inherent precision of those methods (typically <1-5% RSD) and the greater number of elements measured. Glass samples that were manufactured in different plants, or at the same plant weeks or months apart, were readily differentiated by elemental composition when analyzed by these sensitive methods. This journal is © 2013 The Royal Society of Chemistry. Source


Tiscione N.B.,Palm Beach County Sheriffs Office | Vacha R.E.,Orlando Regional Operations Center | Alford I.,Palm Beach County Sheriffs Office | Yeatman D.T.,Palm Beach County Sheriffs Office | Shan X.,Palm Beach County Sheriffs Office
Journal of Analytical Toxicology | Year: 2015

The effect of long-term room temperature storage on the stability of ethanol in whole blood specimens was investigated. One hundred and seventeen preservedwhole blood case samples (110 of 117with two tubes of blood in each case) were used for this study. One tube from each case was initially tested for blood alcohol concentration (BAC) for criminal driving under the influence proceedings. Cases positive for ethanol ranged in BAC from 0.023 to 0.281 g/dL. The second tube, if present, remained sealed. All blood samples were then stored at room temperature. After 5.4-10.3 years, the opened tubes were reanalyzed for BAC by the same laboratory that performed the initial testing using the same method and same instrumentation. After the same storage period, the unopened tubes were sent to a different laboratory, using a different method and different instrumentation, and reanalyzed for BAC after a total of 5.6-10.5 years of room temperature storage. Seven samples initially negative for alcohol remained negative. All samples initially positive for ethanol demonstrated a decrease in BAC over time with a statistically significant difference in loss observed based on blood sample volume and whether or not the tube had been previously opened. The decrease in BAC ranged from 0.005 to 0.234 g/dL. Tubes that were not previously opened and were more than half full demonstrated better BAC stability with 89% of these tubes demonstrating a loss of BAC between 0.01 and 0.05 g/dL. © The Author 2015. Source

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