The forensic analysis of paint fragments can be prone to interference from their complex composition, warn analytical chemists. 

Organic ions or compounds such as talc or barite can interfere with the spectral profiles of certain transition metals. 'Neglecting their influence can lead to misinterpretation of the analysis data obtained,' said Frank Vanhaecke, professor of analytical chemistry at Ghent University.

Vanhaecke and colleagues have refined the spectroscopic method used in forensics.  They say they can eliminate interference by using a field-based mass spectrometer, which can weed out interfering ions on the basis of their mass-to-charge ratio.

The analysis of small fragments of paint left behind at the scenes of car accidents can be used to match them to a specific vehicle. The forensic study of the paint includes analysis of the pigment types or additives present as well as its physical nature - colour, thickness, multiple layers, etc. Several techniques are used in forensic analysis, including highly sensitive mass spectrometry.

Laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) is used for forensic elemental analysis, with its high resolution and detection range of below parts-per-billion. Major, minor and trace elements can be detected and in this way car paints of the same colour can be discriminated from one another on the basis of elemental composition.

The team, which includes researchers from the Belgian National Institute for Criminology and Criminalistics, has suggested that measuring the ratio of the target elements to titanium (present at high concentrations in most primers) is a first step towards finding hit-and-run culprits.

Michael J Spencelayh