RAPID COMMUNICATIONS IN MASS SPECTROMETRY Rapid Commun. Mass Spectrom. 2005; 19: 1899–1905 Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/rcm.2000 13 C-Isotope ratio mass spectrometry as a potential tool for the forensic analysis of white architectural paint: a preliminary study L. J. Reidy*, W. Meier-Augenstein and R. M. Kalin Environmental Engineering Research Centre, Queen’s University of Belfast, David Keir Building, Stranmillis Road, Belfast BT9 5AG, UK Received 14 January 2005; Revised 7 May 2005; Accepted 7 May 2005 Paints have a dual role in society, to protect materials from environmental agents such as ultraviolet light, moisture and oxygen, and to make painted materials look more attractive. Variability in paint samples is often due to binder and pigment type within the sample. The most common resin used in decorative paints is drying oil alkyd resin, which incorporates soybean oil and vinyl acrylic based latexes. Traditional analytical methods used by forensic scientists may be able to say whether two paint samples are indistinguishable but cannot conclusively say that they both origi- nate from the same source. To find out if isotopic composition can provide an added dimension of information, 28 different white architectural paints were analysed for 13 C abundance using isotope ratio mass spectrometry. In addition, variations in application, drying time and thickness were also investigated to assess the discriminatory power of 13 C data from white paints with an unknown history. Preliminary results indicate that this method could aid screening of paint samples. Copyright # 2005 John Wiley & Sons, Ltd. Paints have a dual role in society. First, to protect materials from environmental agents such as ultraviolet light, moisture and oxygen, and secondly to decorate the material to which they are being applied, thus allowing the concealment of imperfections. Paints can be broadly divided into two cate- gories; decorative or architectural paints, and industrial paints. 1 Paint consists of three main elements, binder, pigment and solvent. In addition to these components it contains various additives, for example, dispersing agents, plasticisers, driers, antifungal substance and rust inhibitors. 2 The chemical composition of paints can differ and depends on whether the paints are emulsion polymers or solvent based (Table 1). The two classifications of paint differ in the physical form of the binder, the nature of the carrying solvent and in the chemistry of the drying process (Dr. Peter White, personal communication, 2002). Binders have evolved from naturally available vegetable oils, gums and resins. In modern society, these resins are largely based on synthetic polymer materials with the incorporation of some natural products. 4 There is a vast range of resins and polymers added to paints. High molecular weight resins include nitrocellulose, acrylic and polyvinyl acetate, and low molecular weight resins, which incorporate alkyds, amino resins and epoxides. 5 Alkyds that are to be air-dried contain a moderate oil content, and many of the cross-links form after application. The most common resins used in decorative paints are drying oil alkyd resins that incorporate soybean oil, and vinyl acrylic based latexes, which are used in solvent-based paints. 1 Paint is commonly encountered as trace evidence in a forensic laboratory. 6 This material is usually a result of trace evidence transfer. The presence of paint on a foreign surface is regarded as being evidentially significant since it indicates contact with a surface. 7 At forensic laboratories, paint fragments are subjected to a variety of tests. An excellent guide to paint analysis is found in the SWGMAT document entitled ‘‘A Forensic Paint Analysis Guideline’’. 6 Mass spectrometric methods have been applied to paint for several years. The most common method is pyrolysis/gas chromatography/mass spectroscopy (Py/GC/MS), 7,8 which gives additional information on polymer type and the additives present. GC/MS has been used in several aspects of identifying paint including the characterisation of paint varnish. 9–12 Problems can arise when analysing alkyds modified with silicones, aminoresins and nitrocellulose paints by Py/GC/MS. This method does, however, yield good discrimination when analysing acrylic and vinyl acetate paints. 7 Laser ablation inductively coupled plasma techni- ques 13 complement the characterisation of inorganic compo- nents in paints by analysing their metal composition. This information supplements that from techniques such as scanning electron microscopy-energy dispersive spectro- metry (SEM-EDS), which also determines the elemental composition of the sample. These analytical techniques provide information on che- mical composition, layer sequences, colour and additives of paints. 14 The evidential value is dependent on the significant individuality in these paints. Forensic paint examiners encounter problems when trying to reach any type of Copyright # 2005 John Wiley & Sons, Ltd. *Correspondence to: L. J. Reidy, Environmental Engineering Research Centre, Queen’s University of Belfast, David Keir Building, Stranmillis Road, Belfast BT9 5AG, UK. E-mail: l.reidy@qub.ac.uk