Comparative Bullet Lead and Antimony Analysis using XRF and ICP-OES

1.  Comparative Bullet Lead and Antimony Analysis using XRF and ICP-OES Rob Harvey Nate Birth

2. Background • When the physical markings of a fired bullet recovered from a crime scene are too mutilated for visual comparison or the firearm used in the crime is not recovered, the bullet can be compared with other bullets associated with a suspect by its elemental composition (Peters, 2002)

3. Background • During the manufacturing processes, thousands of lead specimens (bullets and bullet cores) are produced with analytically indistinguishable compositions. However, those lead specimens that share the same composition are generally packaged within the same box of cartridges, or in boxes of cartridges of the same caliber and type at the same manufacturing plant, on or about the same date (Peters, 2002)

4. Background • In one research effort, the group acquired and analyzed samples from bullet lead manufacturers. The results of these analyses confirmed that a cast billet poured from a pot of molten lead is relatively homogeneous, but that leads poured from separate molten batches are distinguishable. As a result, comparative bullet lead analysis has been adopted by laboratories and accepted by courts internationally (Peters, 2002)

5. Significance • Compositional bullet lead comparisons are possible because each melt of lead has its own characteristic composition (Peters, 2002) • Also backed by a study in 2005 by Koons and Buscaqlia • Looked at 1837 samples, determined that 76% of them can be distinguished from one another

6. Quote from FBI • "The bullet removed from the victim and 10 of the 15 analyzed cartridges from the suspect residence are analytically indistinguishable from one another. Therefore, they likely originated from the same manufacturer's source (melt) of lead.” (Peters, 2002) • This conclusion does not associate a bullet to a box but rather to a melt of lead that has bullet specimens within that box and perhaps other boxes.

7. Methods

8. 4 Bullet Samples Flowchart Run in XRF Dissolve Bullets Run in ICP-OES Compare Bullets

9. Bullet Samples • Bullet 1 • Fired, Smashed, Full Metal Jacket • Bullet 2 • Unfired, Hollow Point • Bullet 3 • Unfired, Standard • Bullet 4 • Unfired, Standard

10. XRF Runs • XRF works by exciting the sample • Reads the unique X-rays given off • Gives percentage amount of metals • Bullets ran, and the resulting table printed

11. Bullet Dissolving Method • Concentrated Nitric Acid was used • Bullets were cut with a hack saw • Shavings were weighed as close to 1.00 g as possible • The bullets sat in the acid for a week

12. ICP-OES • Standards were made for both lead and antimony for 10, 20, 30, 40, 50, 75, 100, and 500 ppm • Samples spiked with 2 ppm of both metals, before dilution, after dilution, value is 0.20 ppm • The bullet/acid solution was diluted to 50 ml with a volumetric flask, and then later to 500 ml • Standards were ran to make a calibration curve • Samples were ran to plot on the curve

13. Calculations • To get total ppm of the dissolve bullet: • To make standard solutions: • Experimental values were calculated using the linear regression equation • Percent Composition from ICP:

14. Results

15. XRF Data

16. ICP Calibration Curve Table

19. Bullet ppm Levels • Bullet 1 – 2136 ppm • Bullet 2 – 2004 ppm • Bullet 3 – 2000 ppm • Bullet 4 – 2014 ppm

20. Experimental Lead Levels • Bullet 1 – 150.8 ppm • Bullet 2 – 1391.0 ppm • Bullet 3 – 1077.3 ppm • Bullet 4 – 385.5 ppm

21. Experimental Antimony Levels • Bullet 1 – 0 ppm • Bullet 2 – 1.26 ppm • Bullet 3 – 0.016 ppm • Bullet 4 – 6.83 ppm

22. Summary Table

23. Discussion

24. Evaluation of Method • Used the XRF and ICP-OES to look at bullet composition • XRF provided a fast accurate analysis • ICP-OES was able to detect lower levels of analytes • Detected antimony in all samples but 1, XRF only found 2 bullets with antimony • Bullet Dissolving process could be changed

25. Issues to be Addressed • Dissolving process • Not everything dissolved, longer sonication could result in more material dissolving • Place watch glass on top of beaker • ICP Runs • Concentration of the bullets was higher then expected, not enough dilution was done • Calculating ppm and percent composition • Account for the fact that not all the mass measured was dissolved, lead to percents from ICP to be low

26. Comparison of Bullets • Concept that different bullets have different compositions was shown • XRF data and ICP-OES data both shows this • Lead varied among the bullets, but was always the most prevalent • Antimony was found in all bullets but one, so it could be a good analyte to look for

27. Future Studies • Increase Sample Size • Compare different brands • Compare different types • Look at different metals

28. Overall • Project showed that the levels of lead and antimony vary between bullets • Method is fairly straightforward and solid • Has kinks that need to be worked out • Issue of using a watch glass to minimize evaporation, diluting the sample enough, and accounting for undissolved mass • With the few issues resolved this method can be used to help possibly identify bullets at crime scenes that have been too badly damaged for visual study

29. Literature Cited • Forensic significance of bullet lead compositions RD Koons and J. BuscaqliaJournal of Forensic Science 2005 50(2), 341-351 • The Basis for Compositional Bullet Lead Comparisons CharlesA. Peters Forensic Science Communications 20024(3)