Analysis of Art Objects Using Mass Spectrometry

This presentation reviews the latest progress in the identification of the proteinaceous materials and organic dyes presented in art and in historical building materials using mass spectrometry as a dominant method. The method of the peptide mass mapping for identification of proteinaceous binders in the colour layers of easel paintings and in the historical mortars was developed in our laboratory. It is based on specific enzymatic cleavage and subsequent analysis of the peptide mixture by MALDI-TOF MS (matrix-assisted laser desorption/ionisation time of flight mass spectrometry). The obtained mass spectrum creates a "mass fingerprint", which enables reliable identification by comparison of the spectrum of the analysed sample with those of reference samples from our library. The developed method was tested on the model and real colour layers as well as on the fresh and naturally aged model mortar samples and on the several hundred years old building materials. The direct analysis of organic dyes by mass spectrometry is based on identification of their molecular ions. No preliminary treatment of the sample is needed. The method was successfully applied on the microscopic amounts of pure dyes and organic pigments, on the fragments of colour layers in the weight of a few micrograms, and on the individual textile fibres. INTRODUCTION Identification of Proteins in Colour Layers of Easel Paintings and Historical Building Materials Identification of a small amount of a protein (in order of tens of picomoles) is nearly impossible by traditional methods of chemical analysis – e.g. gas chromatography [1-3], pyrolysis-gas chromatography [4,5], and high performance chromatography [4]. The situation is further complicated when a protein mixture of variable composition should be identified in complex matrix containing dyes, oils, inorganic pigments, lime, etc.; moreover, the analysed materials come often from the Middle Ages or even ancient times and the proteins in them could have undergone various modifications (e.g. oxidation, photodecomposition, microbial digestion) over the centuries. Luckily, during the last two decades, the methodology for mastering this challenging task has been developed by biochemists. The branch of biochemistry that seeks to identify all or at least the great majority of proteins occurring in cell, tissue or even entire organism under the given physiological or pathological conditions is called proteomics. Its experimental procedure is usually based on three steps: 1. Protein (as pure as possible) is specifically cleaved with certain protease under defined conditions. Bovine trypsin, which cleaves peptide chains after the positively charged amino acids of lysine and arginine, is used most frequently. Thus, the mixture of peptides, specific for the given protein, is obtained. 1 9th International Conference on NDT of Art, Jerusalem Israel, 25-30 May 2008 For more papers of this publication click: www.ndt.net/search/docs.php3?MainSource=65