ORIGINAL PAPER The identification of synthetic organic pigments in modern paints and modern paintings using pyrolysis-gas chromatography–mass spectrometry Joanna Russell & Brian W. Singer & Justin J. Perry & Anne Bacon Received: 10 January 2011 /Revised: 17 February 2011 /Accepted: 19 February 2011 /Published online: 17 March 2011 # Springer-Verlag 2011 Abstract A collection of more than 70 synthetic organic pigments were analysed using pyrolysis-gas chromatogra- phy–mass spectrometry (Py-GC–MS). We report on the analysis of diketo-pyrrolo-pyrrole, isoindolinone and per- ylene pigments which are classes not previously reported as being analysed by this technique. We also report on a number of azo pigments (2-naphthol, naphthol AS, arylide, diarylide, benzimidazolone and disazo condensation pig- ments) and phthalocyanine pigments, the Py-GC–MS analysis of which has not been previously reported. The members of each class were found to fragment in a consistent way and the pyrolysis products are reported. The technique was successfully applied to the analysis of paints used by the artist Francis Bacon (1909–1992), to simultaneously identify synthetic organic pigments and synthetic binding media in two samples of paint taken from Bacon’ s studio and micro-samples taken from three of his paintings and one painting attributed to him. Keywords Py-GC–MS . Francis Bacon . Synthetic organic pigment . Pyrolysis . Art . Mass spectrometry Introduction Over the twentieth century, increasing numbers of synthetic organic pigments have been introduced and used in industrial, household and artists’ paints. Conservators, conservation scientists and art historians often wish to identify the pigments present in a work of art; however, the identification of modern organic pigments often presents greater difficulties to the analyst compared with that of inorganic artists’ pigments. The elemental analysis techni- ques which have been proven so useful for the identifica- tion of inorganic pigments are not so effective with organic pigments, where the range of elements is small. In addition, these pigments often have very small particle sizes, meaning optical microscopy cannot be used effectively. Many have high tinting strength, meaning a low concen- tration of pigment is needed to colour the paint so little will be present for analysis. The rapid development of new organic pigments also complicates identification, as this has led to a far greater range of different colorants being used in artists’ paints than was the case with traditional pigments. A wide variety of different methods have been described for the analysis of synthetic organic pigments. The large number of different structures means there is often a lack of reference data to aid in identification, especially given the spread of methods and research. A recent review described the different classes of synthetic organic pigments before going on to discuss methods for their identification [1]. Other reviews discuss the history, synthesis and uses of specific classes of pigments, and also include information on methods of identification. Such papers have been published on the subject of azo pigments [2], phthalocya- nine and quinacridone pigments [3] and arylide yellows [4]. Techniques which have been applied to the identification of modern organic pigments include: Fourier transform infra- red spectroscopy (FTIR) [5–8], Raman spectroscopy [8– 11], pyrolysis-gas chromatography–mass spectrometry (Py- GC–MS) [7, 12–14], direct temperature mass spectrometry [5, 7, 15, 16] and laser desorption (ionisation) mass J. Russell : B. W. Singer : A. Bacon School of Arts and Social Sciences, Northumbria University, Newcastle upon Tyne NE1 8ST, UK B. W. Singer (*) : J. J. Perry School of Life Sciences, Northumbria University, Newcastle upon Tyne NE1 8ST, UK e-mail: brian.singer@northumbria.ac.uk Anal Bioanal Chem (2011) 400:1473–1491 DOI 10.1007/s00216-011-4822-9