Solid sampling electrothermal vaporization inductively coupled plasma optical emission spectrometry for discrimination of automotive paint samples in forensic analysis

Abstract

Pieces of automotive paint often constitute trace evidence at crime scenes, especially in hit-and-run cases. As minute amounts of sample generally are available for forensic analysis, sensitive direct analysis methods are preferable to multi-step methods that may lead to sample contamination and/or analyte loss. Such a simple method was developed for discrimination of automotive paint samples. It involves solid sampling electrothermal vaporization (ETV) coupled to inductively coupled plasma optical emission spectrometry (ICP-OES) and multivariate analysis. A total of 18 automotive paint fragments were collected by scraping six red-colored car wrecks from three sides (front, side and back). Two replicates of each paint fragment were analysed. In each case, 0.8-2.0 mg paint was directly weighed onto an ETV graphite boat, which was then inserted into the ETV furnace for vaporization at 2200 C. The vaporization products were carried into the ICP by Ar carrier gas containing dichlorodifluoromethane reactant gas. For classification of paint samples according to their sources, several elements were simultaneously monitored. No sample pretreatment or quantification of the elements was needed. Point-by-point normalization of the emission signal of each analyte to an Ar emission line was carried out, followed by integration of the resulting transient signal. The data matrices composed of the integrated areas (divided by sample mass) for the different elements were then subjected to principal component analysis (PCA), cluster analysis and linear discriminant analysis (LDA). After identifying the major contributing variables by PCA, LDA was performed and showed that a combination of three/four variables from Cr, Pb, Sn, and Zn correctly assigned each of 18 red paint samples to the correct source car. Hence, solid sampling ETV-ICP-OES, which only requires a very small amount of sample, is a simple technique for forensic automotive paint analysis, i.e. for the identification of the make and model of a car in question.

Atomic spectrometry update: review of advances in the analysis of metals, chemicals and materials

“…Solid sampling electrothermal vaporisation coupled with ICP-OES has been developed for the discrimination of automotive paint samples. 135 In this paper, 18 samples of paint fragments were collected from 6 red car wrecks, sampled from the front, side and back. For each sample, 2 replicates of 0.8 to 2.0 mg of paint were weighed directly onto a graphite ETV boat which was placed into the ETV furnace for vaporisation at 2200 C. The vapour was then transferred into the ICP in an Ar carrier containing Cl 2 F 2 C reactant gas.…”

Improvements in the direct analysis of advanced materials using ICP-based measurement techniques

“…Although quantitative measurements are desired in most cases, it has to be considered that quantication is not always necessary. Asfaw et al 45 have successfully discriminated between different types of red automotive paint chips, only by normalizing the signals to the sample intake and to one argon emission line. The temporal changes in the argon emission lines reect the conditions in the ICP.…”

Heavy metal ion detection using a capacitive micromechanical biosensor array for environmental monitoring

“…Toward this goal, a number of Pb 2+ sensing techniques have been developed. While spectroscopic techniques, such as atomic absorption spectroscopy and inductively coupled plasma atomic emission spectroscopy, can offer high sensitivity for Pb 2+ detection [9] the need for accurate, on-site and real time measurements has led to the development of sensors based on biomolecules that fulfill these requirements without compromising neither on selectivity nor sensitivity. Among them, DNAzymes have emerged recently as a promising class of molecules to build sensors.…”