Sampling strategies for the analysis of glass fragments by LA-ICP-MS Part II: Sample size and sample shape considerations.

Glass fragments recovered from crime scenes are usually very small and therefore the amount of sample available to conduct forensic analyses is limited. Elemental analysis using conventional digestion methods consumes at least 2-3mg of glass per replicate. LA-ICP-MS requires 10,000 times less glass consumption per analysis ( approximately 280ng), and therefore the sample remains practically unaltered. Typically, the recovered fragments (unknowns) are 0.1-1mm in length, while the "known" samples are usually larger, i.e. a broken fragment from a windshield (>3mm). For bulk digestion analysis, the difference in fragment size does not present a problem for elemental comparisons - other than requiring at least 6mg for triplicate analysis - because the sample is crushed and homogenized before weighing. Laser ablation sampling results in the creation of small craters ( approximately 50mum diameter and 80mum deep) drilled into the sample due to the interaction of the laser with the glass target. This study aims to evaluate whether the quantitative elemental analysis using the LA sampling method is affected by the size of the glass fragment due to differences in heat dissipation and surface-laser interaction. The analytical method employed for the analysis of glass by LA-ICP-MS had previously shown to possess the same or better performance than dissolution ICP-MS methods in terms of accuracy, precision, limits of detection and discrimination power. A 266nm Nd:YAG laser with a flat top beam profile was used in single point mode sampling a 50mum spot size for 50s at 10Hz. Standard glass reference materials SRM 612 and SRM 610 were selected to conduct this work in order to account for different concentration ranges and different opacities of the samples. The set under study was comprised of seven fragments originating from each standard at different sizes and shapes ranging from 6 to 0.2mm length. Analysis of variance (ANOVA) followed by the Tukey's honestly significant different test (HSD) was used for data analysis. The results show that there is no significant difference in the elemental composition of different sized fragments. The conclusions, however, cannot be generalized for fragments measuring less than 0.2mmx0.1mm.

[1]  T. Catterick,et al.  Rapid analysis of small glass fragments by atomic-absorption spectroscopy. , 1978, Talanta.

[2]  Steven Frederick Durrant,et al.  Laser ablation inductively coupled plasma mass spectrometry: achievements, problems, prospects , 1999 .

[3]  D. Grégoire,et al.  Determination of trace elemental signatures in placer gold by laser ablation–inductively coupled plasma–mass spectrometry as a potential aid for gold exploration , 1998 .

[5]  J. Almirall,et al.  Effect of fractionation on the forensic elemental analysis of glass using laser ablation inductively coupled plasma mass spectrometry. , 2004, Analytical chemistry.

[6]  J. Almirall,et al.  Analysis and comparison of glass fragments by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and ICP-MS , 2003, Analytical and bioanalytical chemistry.

[7]  P. Lienemann,et al.  Determination of impurities in antique silver objects for authentication by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) , 1999 .

[8]  H. Stephanowitz,et al.  Investigation of mercury migration in human teeth using spatially resolved analysis by laser ablation-ICP-MS , 2000 .

[9]  Xianglei Mao,et al.  Laser ablation in analytical chemistry-a review. , 2002, Talanta.

[10]  William L. Griffin,et al.  The application of laser ablation-inductively coupled plasma-mass spectrometry to in situ U–Pb zircon geochronology , 2004 .

[11]  R. Russo,et al.  Laser ablation sampling , 1998 .

[12]  C. Bayne,et al.  Analysis of variance in forensic glass analysis by ICP-MS: variance within the method , 2000 .

[13]  J. Buscaglia.  Elemental analysis of small glass fragments in forensic science , 1994 .

[14]  H. Stephanowitz,et al.  Collection and separation of particles by size from laser ablated material , 2002 .

[15]  Andria L. Hobbs,et al.  Trace elemental analysis of automotive paints by laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) , 2003, Analytical and bioanalytical chemistry.

[16]  J. Almirall.  Elemental analysis of glass fragments , 2001 .

[17]  H. Kobus,et al.  THE ANALYSIS OF SMALL GLASS FRAGMENTS USING INDUCTIVELY COUPLED PLASMA MASS SPECTROMETRY , 1996 .

[18]  R. Watling,et al.  Use of Laser Ablation Inductively Coupled Plasma Mass Spectrometry for Fingerprinting Scene of Crime Evidence , 1997 .

[19]  C. Bayne,et al.  Forensic glass analysis by ICP-MS: a multi-element assessment of discriminating power via analysis of variance and pairwise comparisons , 2002 .