Laser Ablation ICP-MS in Forensic Glass Analysis: A Decade of Experience

Transcription

1 Session: New Developments and State of the Art in Trace Evidence Examinations Laser Ablation ICP-MS in Forensic Glass Analysis: A Decade of Experience Bundeskriminalamt Forensic Science Institute Germany KT13@bka.bund.de

2 1996 Trace Symposium San Antonio Wilfried Stoecklein The Forensic Analysis of Float Glass Characterization of Glasses from International Sources LA-ICP-MS in Forensic Glass Analysis

3 The Forensic Analysis of Float Glass Characterization of Glasses from International Sources W. Stoecklein, 1996 Elemental analysis of 61 glasses of global origin (28 Europe, 19 U.S.A., 14 Japan) (38 colorless, 21 green, 2 brown) (13 producers, 7 countries) Elemental analysis (ICP-MS, WDXRF) Determination of RI LA-ICP-MS in Forensic Glass Analysis

4 The Forensic Analysis of Float Glass Characterization of Glasses from International Sources W. Stoecklein, 1996 Liquid digestion: 0,5-2 mg of cleaned glass fragments (from bulk) + hydrofluoric acid, nitric acid, perfluoric acid Hot plate fuming to dryness Resolvation with 5 % nitric acid containing Rh int. std ICP-MS LA-ICP-MS in Forensic Glass Analysis

5 The Forensic Analysis of Float Glass Characterization of Glasses from International Sources Results 10 % of the examined glasses were indistinguishable by RI. Full differentiation of all glasses was possible by ICP-MS. Selection of elements which proved highest discrimination. Characterization of glass origin (Japan, U.S.A., Europe). LA-ICP-MS in Forensic Glass Analysis

6 The forensic Analysis of Float Glass Characterization of Glasses from International Sources Conclusion Quantitative analysis of 30 elements by ICP-MS improves evidential value of glass examination. LA-ICP-MS in Forensic Glass Analysis

7 Laser Laser Ablation carrier gas (He) Glass LA-ICP-MS in Forensic Glass Analysis:

8 Plasma ~7000 C carrier gas and sample MS Total destruction & ionisation of the sample

9 Why LA-ICP-MS? Measurements possible on small samples (~0,5 mm; ~ 0,02 in) No sample preparation (time saving) Quasi non-destructive analysis due to small sample uptake No problems measuring on rough surfaces (as in µ-xrf) Quantitative analysis of 20 major, minor and trace elements in one analytical run LA-ICP-MS in Forensic Glass Analysis:

10 History of instrumentation 1992 Installation of ICP-MS Fisions PQ Addition of UV-laser ablation system (1064 nm) 1997 Exchange of UV by Infrared laser ablation (266 nm) 2003 Replacement of old system with new LA-ICP-MS system (213 nm) LA-ICP-MS in Forensic Glass Analysis

11 ICP-MS Fisions PQ2+ IR-laser ablation VG Microprobe LA-ICP-MS in Forensic Glass Analysis:

12 ICP - MS LA LA-ICP-MS in Forensic Glass Analysis:

13 Why matrix matched standards? Until now SRM NIST 612 (50 ppm) is used for quantitative analysis of float glasses Better results by using a standard: with the same matrix (composition of main elements) with concentration of trace elements in the same range as typical float glass both are not given by NIST 612

14 R&D Project BKA - SCHOTT AG: Development of new calibration standards FGS 1 standard (low concentration) d = 9 cm h = 8 cm

15 R&D Project BKA - SCHOTT AG: Development of new calibration standards BKA-FGS 1: diameter: 10 mm thickness: 3 mm

16 NITECRIME activities on glass EU network project Main focus on float glass (highest forensic interest) Development of a protocol for glass analysis with LA-ICP-MS Evaluation of new calibration standards

17 NITECRIME activities on glass Workpackage 3.1 Instrumental validation ETH Zürich Two interlaboratory tests ( & 3.1.2) Workpackage 3.2 Glass BKA Two interlaboratory tests (3.2.1 & 3.2.2) Introduction of new matrix matchted standards (FGS 1 & 2) In total: Four interlaboratory tests dealing with glass Three interlaboratory tests with similar set-up

18 Instrument combinations: Laser Ablation Mass spectrometer 193 nm 213 nm 266 nm 266 nm high power Sector field ICP-MS Quadrupole ICP-MS

19 Participants of collaborative exercises Curtin University of Technology, Perth, Australia FBI, Quantico Florida International University, Miami ETH Zürich, Swiss Federal Institute of Technology NFI, Rijswijk, The Netherlands US Customs, Springfield BKA, Wiesbaden, Germany

20 NITE CRIME Summary 1/2 Similar quantitative results by labs with completely different LA-ICP-MS combinations (most RSD << 10 % intra-laboratory). Note: Results for float glass, not for std material! Note: Results for embedded glass, not for fragments! A protocol for optimised laser ablation conditions (as given in the fourth interlaboratory test) improved both the precision and the accuracy of quantitative results.

21 NITE CRIME Summary 2/2 The new matrix matched float glass standards FGS 1 and FGS 2 can be used as calibration or tuning standards for the quantitative analysis of float glass. Latkoczy, Becker et al. J. For. Sci. 2005; 50(6):

22 Reanalysis of the 63 float glasses of global origin by LA-ICP-MS Six replicate measurements App. 80 µm crater diameter Single shot Time resolved analysis 10 Hz, 10J/cm2 LA-ICP-MS in Forensic Glass Analysis:

23 Crater dimension: µm Smaller than a hair Nd:YAG-laser 213 nm

24 Variation of main & minor element concentration of 63 float glasses of global origin B o x - W h is k e r P lo t s f o r 6 3 f lo a t g la s s e s ; c o n c e n t r a t io n s m a in & m in o r e le m e n t s in µ g / g M e d ia n 25 % -75% 10 % -90% O u t lie r E x t r e m e v a lu e Na M g Al Si K Ca LA-ICP-MS in Forensic Glass Analysis:

25 Variation of trace element concentration of 63 float glasses of global origin B o x - W h is k e r P lo t s f o r 6 3 f lo a t g la s s e s ; c o n c e n t r a t io n s fo r t r a c e e le m e n t s in µ g / g , ,0 5 0,0 5,0 0,5 M e d ia n 25% -75% 10% -90% O u t lie r E x t r e m e v a lu e s Ti M n Sr Zr La Pb

26 Differentiation of origin by potassium and aluminum content Potassium (µg/g) 8000 E u ro p e U.S.A. Japan A lu m in u m ( µ g / g )

27 Differentiation of container glass from float glass Data set of 63 float glasses of global origin Data set of 20 container glasses of German origin

28 Differentiation of container glass from float glass Mn Ti Ca K flo a t c o n ta in e r g la s s e s flo a t c o n ta in e r g la s s e s 0 0 flo a t c o n ta in e r g la s s e s flo a t c o n ta in e r g la s s e s

29 Differentiation of container glass from float glass flo a t g la s s e s c o n t a in e r g l a s s e s Pb [ µg/ g] C a /M g

30 Analysis of small fragments sec Integration Time Counts per Second Fragment µg Time [sec] Time resolved analysis signal of Cerium from fragment 6

31 Analysis of small fragments sec Integration Time Counts per Second Fragment µg Time [sec] Time resolved analysis signal of Cerium from fragment 4

32 Analysis of small fragments sec Integration Time Counts per Second Fragment Time [sec] Time resolved analysis signal of Cerium from fragment 6

33 Findings 0,1-1,5 % lower RSD are achieved when excluding the results of the two measurements of fragment 3. Care should be taken when investigating very small and flat fragments, where only one or two shots are possible due to quantification problems with short TRA signals resulting in poorer reproducibilities.

34 Step by step approach in forensic glass analysis Glass case Physical examinations/ GRIM Chemical examinations (ICP-MS, SEM, XRF) samples distinguishable case report case report

35 Investigation of change of RI by LA interaction Side view mean RI (pre-ablation) = 1,51927 ± 3x10-5

36 FBI/BKA homogeneity study 2006 FBI laboratory bought commercial window pane FBI: GRIM, ICP-OES BKA: LA-ICP-MS measurements on 44 fragments from the same source

37 Flat Sheet Diagram Sheet 48 x48 Squares 4 x4-4 inch samples - 1 inch samples

38 Results of the homogeneity study RI analysis glass displays homogeneity The sheet does not show any trend in variation but varies as a whole within the expected range. ICP-OES analysis glass displays homogeneity There are no noticeable trends in the sheet. The error associated with the method is larger than the variation in the sheet.

39 Results of the homogeneity study LA-ICP-MS: RSD for the mean values of 44 samples 8% 6% 4% 2% Pb Hf Nd Ce La Ba Sn Zr Sr Rb Fe Mn Ti Ca K Al Mg Na Li 0% Analysis of variance significant influence of sample inhomogeneities on LA-ICP-MS results for several elements (Al, Zr, Hf, Pb) - due to the high spatial resolution of the method (sampling of 2 µg instead of mg) micro heterogeneity of the glass

40 Match criterion Glass fragments originating from different sources Glass fragments originating from the SAME source = Error Type I Error Type II =

41 Possible match criteria Hotellings T²-Test: requires more measurements than elements (i.e.20) impractical T-Test: often two fragments of the same glass can be discriminated too many Type I errors N-sigma criteria: best choice for our application

42 Optimization of the match criterion Amount of errors type I and type II in dependence on n and m 1000 I Fehler Error2. Art type II Number of errors Fehler Error1. Art type Match criteria (n-sigma & m "allowed" elements)

43 Optimised Match Criterion 4-sigma criterion 0 element may be distinguishable FBI-Glass: 44 data sets, 946 pairwise comparisons Type I errors: 10 (1,06 %) 05_Stat: 63 data sets, 1953 pairwise comparisons Type II errors: 3 (0,15 %) =

44 Summary Introduction of matrix matched std FGS 1 & 2 NITE CRIME activity: LA-ICP-MS produces accurate data for the comparison of float glasses (protocol) FBI/BKA glass project (micro homogeneity & type I error) Reanalyses of 63 float glasses of global origin (type II errors) Optimized match criterion: 4-sigma criterion Further validation led to ISO accreditation of LA-ICP-MS method in May 2007 Routine application in casework

45 Thanks Thanks to Maureen Bottrell, Jodi Webb & Robert Koons (FBI). Special thanks to Dr. Peter Weis, Marc Dücking, Peter Watzke/BKA. Thanks to all NITECRIME members for their support, especially: J. Almirall, FIU, U.S.A. J. Buscaglia, R. Koons, FBI Academy, U.S.A. D. Günther, C. Latkoczy, ETH Zürich, Switzerland S. Montero, G. van der Peijl, NFI, Netherlands J. Watling, Curtin University, Perth Australia, V. Zdanowicz, U.S. Customs, U.S.A.