Session: New Developments and State of the Art in Trace Evidence Examinations Laser Ablation ICP-MS...

Session: New Developments and State of the Art in Trace Evidence Examinations

Laser Ablation ICP-MS in Forensic Glass Analysis:

A Decade of Experience

BundeskriminalamtForensic Science Institute

Germany

[email protected]

LA-ICP-MS in Forensic Glass Analysis

1996 Trace Symposium San AntonioWilfried StoeckleinThe Forensic Analysis of Float GlassCharacterization of Glasses fromInternational Sources


The Forensic Analysis of Float Glass -Characterization of Glasses from International SourcesW. 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


The Forensic Analysis of Float Glass -Characterization of Glasses from International SourcesW. 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


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).


The forensic Analysis of Float Glass -Characterization of Glasses from International Sources

ConclusionQuantitative analysis of 30 elements by ICP-MS improves evidential value of glass examination.

LA-ICP-MS in Forensic Glass Analysis:

Laser Ablation

Lase

r

Glass

Lase

rLa

ser

Glass

Lase

r

carrier gas (He)

Plasma~7000 °C

carrier gas and sample MS

Total destruction & ionisation of the sample


• 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

Why LA-ICP-MS ?

History of instrumentation

1992 Installation of ICP-MS Fisions PQ2+

1996 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)



ICP-MS Fisions PQ2+ IR-laser ablation VG Microprobe


LA

MSICP -

• 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

Why matrix matched standards ?

both are not given by NIST 612

FGS 1 standard(low concentration)

d = 9 cmh = 8 cm

R&D Project BKA - SCHOTT AG:Development of new calibration standards

BKA-FGS 1:diameter: 10 mm thickness: 3 mm

R&D Project BKA - SCHOTT AG:Development of new calibration standards

NITECRIME activities on glass

• EU network project 2001-2005

• Main focus on float glass (highest forensic interest)

• Development of a protocol for glass analysis with LA-ICP-MS

• Evaluation of new calibration standards

Workpackage 3.1 Instrumental validation ETH

Zürich Two interlaboratory tests (3.1.1. & 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 glassThree interlaboratory tests with similar set-

up

NITECRIME activities on glass

Instrument combinations:

193 nm

213 nm

266 nm

266 nm high power

Sector field ICP-MS

Quadrupole ICP-MS

Laser Ablation Mass spectrometer

Participants of collaborative exercisesCurtin University of Technology, Perth, AustraliaFBI, QuanticoFlorida International University, MiamiETH Zürich, Swiss Federal Institute of Technology NFI, Rijswijk, The NetherlandsUS Customs, SpringfieldBKA, Wiesbaden, Germany

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.

•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.

NITE CRIME Summary 2/2

Latkoczy, Becker et al. J. For. Sci. 2005; 50(6):1327-1341


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

Crater dimension: 5 - 100 µm

Nd:YAG-laser 213 nm

Smaller than a hair


Variation of main & minor element concentration

of 63 float glasses of global origin

Box-W hisker P lots for 63 float g lasses; concentrations m ain & m inor elem ents in µg/ g

Na Mg Al Si K Ca50

500

5000

50000

500000

M ed ian 25% -75% 10% -90% O utlier Extrem e value

Variation of trace element concentration of 63 float glasses of global origin

Box-W hisker P lots for 63 float g lasses; concentrations for trace elem ents in µg/ g

Ti Mn Sr Zr La Pb0,5

5,0

50,0

500,0

5000,0

M ed ian 25% -75% 10% -90% O utlier Extrem e values

Differentiation of origin by potassium and aluminum content

Alum inum (µg/ g)

Potassium (µg/g)

0 2000 4000 6000 8000 10000 120000

2000

4000

6000

8000

10000

E uropeU.S .A .Japan

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


float container

g lasses

0

2000

4000

6000

8000

10000

12000

39K

float container

g lasses

0

100

200

300

400

500

600

49Ti

float container

g lasses

0

50

100

150

200

250

300

350

400

55M

n

float container

g lasses

0

10000

20000

30000

40000

50000

60000

70000

80000

90000

42C

a

C a/M g

Pb [µg/g]

0 2 4 6 8 10 12 14 160

20

40

60

80

100

120

140

160

180

200

220

240

float g lassescon tain er g lasses


0

20000

40000

60000

80000

100000

120000

0 20 40 60 80 100

Time [sec]

Cou

nts

per

Se

cond

30 secIntegrationTime

Fragment 6271 µg

Time resolved analysis signal of Cerium from fragment 6

Analysis of small fragments

0

20000

40000

60000

80000

100000

120000

0 20 40 60 80 100

Time [sec]

Co

unts

per

Sec

ond


Fragment 4193 µg



0

20000

40000

60000

80000

100000

120000

0 20 40 60 80 100

Time [sec]

Cou

nts

per

Sec

ond


Fragment 3



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.

Glass case

Physical examinations/ GRIM case report

Chemical examinations

(ICP-MS, SEM, XRF)case report

samples distinguishable

Step by step approach in forensic glass analysis

Side view

mean RI (pre-ablation) = 1,51927 ± 3x10-5

Investigation of change of RI by LA interaction

FBI/BKA homogeneity study2006

• FBI laboratory bought commercial window pane

FBI: GRIM, ICP-OES BKA: LA-ICP-MS

• measurements on 44 fragments from the same source

Flat Sheet DiagramSheet – 48”x48” Squares – 4”x4”

1 2 3 4 5 6 7 8 9 10 11 12

13 14 15 16 17 18 19 20 21 22 23 24

25 26 27 28 29 30 31 32 33 34 35 36

37 38 39 40 41 42 43 44 45 46 47 48

49 50 51 52 53 54 55 56 57 58 59 60

61 62 63 64 65 66 67 68 69 70 71 72

73 74 75 76 77 78 79 80 81 82 83 84

85 86 87 88 89 90 91 92 93 94 95 96

97 98 99 100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

131

132

133

134

135

136

137

138

139

140

141

142

143

144

- 4 inch samples- 1 inch samples

• 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.

Results of the homogeneity study

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

Results of the homogeneity study

LA-ICP-MS: RSD for the mean values of 44 samples

0%

2%

4%

6%

8%

Li

Na

Mg Al K C

a Ti

Mn Fe

Rb Sr Zr

Sn

Ba

La

Ce

Nd Hf

Pb

Match criterion

Glass fragments originating from different sources

Glass fragments originating from the SAME

source

= Error Type II

=Error Type I

• 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

Possible match criteria

Amount of errors type I and type II in dependence on n and m

1

10

100

1000

2--0

2--1

2--2

2--3

3--0

3--1

3--2

3--3

4--0

4--1

4--2

4--3

6--0

6--1

6--2

6--3

10--010

--110

--210

--310

--520

--6

Match criteria (n-Sigma & m "allowed" elements)

Num

ber

of e

rror

s

Fehler 1. Art

Fehler 2. Art

Optimization of the match criterion

Error type IError type II

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 %)

=

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 17025 accreditation of LA-ICP-MS method in May 2007

• Routine application in casework

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, SwitzerlandS. Montero, G. van der Peijl, NFI, NetherlandsJ. Watling, Curtin University, Perth Australia,V. Zdanowicz, U.S. Customs, U.S.A.

A. Walther, SCHOTT AG, for the good co-operation.

Thanks

Session: New Developments and State of the Art in Trace Evidence Examinations Laser Ablation ICP-MS...

Documents

Transcript of Session: New Developments and State of the Art in Trace Evidence Examinations Laser Ablation ICP-MS...