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Forensic Applications of LA-ICP-MS: Elemental Profiling and Homogeneity in Soda-Lime Glass

This study explores the use of laser ablation (LA)-ICP-MS for elemental profiling and evaluation of homogeneity in soda-lime container glass. The research aims to determine the consistency of elemental profiles in glass bottles, appropriate match-criteria, and variability within a manufacturer. The results show that bottles manufactured from the same furnace are typically indistinguishable, while bottles manufactured from different furnaces can be distinguished.

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Forensic Applications of LA-ICP-MS: Elemental Profiling and Homogeneity in Soda-Lime Glass

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  1. FORENSIC APPLICATIONS OF LA-ICP-MS: ELEMENTAL PROFILING AND EVALUATION OF HOMOGENEITY IN SODA-LIME CONTAINER GLASS Karen J. Harrington

  2. Inductively Coupled Plasma Mass Spectrometry (ICP-MS) • Previous method of RI predominantly used • Elemental analysis research began three decades ago • Allows classification of product type and use • Shown to be a discriminating technique for forensic analysis • Drawbacks • Dangerous digestions • Sample size requirements • Destructive nature

  3. Laser ablation (LA)-ICP-MS • A viable method for forensic glass comparisons • Creates aerosol of super-fine glass fragments • Advantages • Decreased sample prep. time • Minimal sample consumption • Maintains good sensitivity for most elements • Less risk of contamination

  4. Homogeneity • Are elements consistent within a glass item (micro-homogeneity)? • Natural heterogeneity (result of manufacturing) Contamination, natural variation in raw material • How do elements vary between glass items? • Variation beyond natural fluctuation?

  5. Previous Research on Homogeneity • LA-ICP-MS does reveal natural variations in glass • Understanding homogeneity within a unit of glass is a factor when: • Comparing samples from different categorical sources • Comparing samples from different manufacturers

  6. Homogeneity • Glass items typically maintain some homogeneity overall • Glass of the same type can often be distinguished on an item-item basis • Glass bottles tend to be more variable and may not be distinguishable from each other within one manufacturer

  7. Project Goals • How consistent are elemental profiles in glass bottles? • What are appropriate match-criteria to balance false positives and false negatives? • How variable are glass bottles within a manufacturer?

  8. Background – Stage I • Verify valid set of match-criteria • Examine homogeneity of a single bottle • Determine what criteria allow for treatment of bottle as a whole unit

  9. Background – Stage II • Determine normal/natural manufacturer variability • Hourly runs • Daily runs • Simultaneous/daily for multiple furnaces

  10. Method – Sample Selection • Gallo Glass Company, Modesto, CA • Typical soda-lime, with cullet (25% recycled) • Stage 1 • 10 bottles from two furnaces, variable time intervals, colors, types (3 fragments each from neck, sidewall, base regions of each bottle) • Stage 2 • Hourly, daily, daily simultaneous furnace

  11. Method – Analyte Selection • Analytes were selected from an acid digestion of selected bottles from the population. • Ratios were determined based on %RSD and mass-to-charge values.

  12. Method – Comparison Criteria • T-tests and ANOVA were found to be unacceptable for the purposes of this project. • Typical case-work match-criteria of ±2 SD was used

  13. a b Method – Instrumentation • Perkin-Elmer ELAN DRC II ICP-MS (a) • New Wave Research Nd: YAG LA (1 = 213nm) unit (b) a, b Dodds, A.J., Land, D.P., Pollock, E.M. Determination of Elemental Homogeneity in Automotive Windshields by LA-ICP-MS. The CACNews. 4th Quarter 2005. 17 – 20.

  14. Results – Stage I • 10 comparison of multiple regions showed indistinguishable elemental profiles for 13 ratios with ± 2SD. • When ± 3SD was applied to Sr/Zr and Fe/Cr (the two consistently problematic ratios), all 10 bottles showed indistinguishable elemental profiles for 15 elements.

  15. Results – Stage I

  16. Results – Stage I

  17. Results – Stage I

  18. Results – Stage I

  19. Results – Stage 2 (hourly) * Group 1 (one bottle distinguishable for 1 element) and Group 2 (two bottles distinguishable for 3 elements) show some distinguishable elemental profiles from other bottles.

  20. Results – Stage 2 (hourly) * Group 1 (bottle # 38 for 1 element) and Group 2 (bottles #48 and #50 for 3 elements) show some distinguishable elemental profiles from other bottles.

  21. Results – Stage 2 (daily) * 1 bottle was indistinguishable from another that was 11 days apart

  22. Results – Stage 2 (daily) *1 bottle was only distinguishable from others that were 11 days or more apart.

  23. Results – Stage 2 (simultaneous daily)

  24. Results – Stage 2 (simultaneous daily)

  25. Conclusion - hourly • Bottles manufactured from the same furnace are typically not distinguishable when compared hourly • 80 – 90% of bottles manufactured within a daily production lot from the same furnace share indistinguishable elemental profiles

  26. Conclusion - daily • Bottles manufactured from the same furnace between 4 and 8 days apart (11 maximum) are typically distinguishable.

  27. Conclusion – simultaneous daily • Bottles manufactured at the same time from different furnaces are distinguishable. • Additionally, some bottles manufactured at the same time on two consecutive days from the same furnace may be distinguishable.

  28. Conclusion – significant information • Supports previous research • Same case/six-pack are indistinguishable 1 • Indistinguishable profiles are typically from same manufacturer 2 • Gallo Glass Company • Produces 800 cases/hour • 1 billion bottles per year • Trejos, T and Almirall, J.R. Sampling strategies for the analysis of glass fragments by LA-ICP-MS Part I. Micro-homogeneity study of glass and its application to the interpretation of forensic evidence. Talanta. 67(2) 388 – 395 (August 2005). • J.R. Almirall. Glass as evidence of association. In Mute Witness; When Trace Evidence Makes the Case, M. Houck (Ed.), Academic Press, San Diego, CA, USE, 139-155 (2001).

  29. Final Conclusions • Still important to collect/examine multiple fragments from question sample 1 • Provides evidentiary value to forensic examinations • Can distinguish between furnaces of same manufacturer • Can distinguish between bottles from the same furnace after approximately 8-11 days 1 Trejos, T and Almirall, J.R. Sampling strategies for the analysis of glass fragments by LA-ICP-MS Part I. Micro-homogeneity study of glass and its application to the interpretation of forensic evidence. Talanta. 67(2) 388 – 395 (August 2005).

  30. Future Research • Multiple manufacturer studies • Bottle distribution (cases, vendors) • More effective statistical studies

  31. Acknowledgments • Sacramento County District Attorney Laboratory of Forensic Services and Staff • Gallo Glass Company • University of California, Davis: Forensic Science Masters program • California Criminalistics Institute

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