Identification of drying oils in mixtures of natural binding media used for artistic and historic works by capillary electrophoresis

Novel analytical methods for characterising binding media and protective coatings in artworks

Since the first reported analytical studies and technical examinations of art and archaeological objects conducted in the late 18th century, analytical techniques and methods applied to the study of artworks have constantly grown. Among the materials composing the art object, organic compounds used as binding media or protective coatings have attracted the attention of the conservation profession given their noticeable ability for undergoing morphological and chemical changes on ageing. Thus, the aim of this paper is to review the most recent advances in the identification and determination of organic compounds present in art and art conservation materials. Immunofluorescence techniques have been proposed in recent decades as an alternative to the classical and simpler microchemical tests. Besides, a variety of instrumental techniques have also been improved in an attempt to enhance the sensitivity, repeatability and accuracy of the analytical results. Spectroscopic techniques, such as UV-vis, FTIR and Raman spectroscopy, have been coupled with light microscopes for these purposes. Synchrotron radiation FTIR microspectroscopy has also been successfully applied to the analysis of artworks. Mass spectrometry has also been increasingly used as a detector system coupled with a chromatographic device. Chromatographic methods have also improved in recent years. Paper and thin layer chromatographic techniques have been progressively replaced with gas chromatography (GC), pyrolysis-GC, high performance liquid chromatography and capillary electrophoresis. More complex proteomics hyphenated techniques, such as nano-liquid chromatography-nano-electrospray ionisation/collision quadrupole time-of-flight tandem mass spectrometry, have been recently applied to the identification and determination of proteinaceous binders. Microbeam analytical techniques have also been incorporated into the list of advanced instrumental techniques for art conservation purposes. Finally, a number of new instrumental techniques have been proposed as a suitable alternative to the conventional microscopy techniques for morphological studies.

Analysis of diterpenoic compounds in natural resins applied as binders in museum objects by capillary electrophoresis

The exudates of conifers consist mainly of diterpenoic acids of the abietane and pimarane type (abietic, neoabietic, dehydroabietic, palustric, pimaric, isopimaric, levopimaric and sandaracopimaric acid) and larixol acetate. These natural resins were used as adhesives, coatings, varnishes or plasticizers in artistic and historic works since ancient times. For the purpose of conservation and restoration and for art historic examination of such museum objects the identification of the binding media used is undoubtedly of paramount importance. In the present paper, the characterization of these resins based on the pattern of their diterpenoid constituents is carried out by capillary electrophoresis. For separation a background electrolyte which has been initially introduced for the analysis of chlorinated and natural resin acids in waste water was modified and the experimental conditions were adjusted in terms of resolution and analysis time. Separation was carried out in borate buffer at pH 9.25 (ionic strength 20 mmol L(-1)) with methyl-beta-cyclodextrin and sulfobutylether-beta-cyclodextrin as additives to increase selectivity and enhance the solubility of the analytes. With this electrophoretic system the resin acids of interest and larixol acetate--all as anionic cyclodextrin complexes--were separated within 5 min and detected at 200, 250 and 270 nm with a diode array detector. The electrophoretic patterns served for the characterisation of the relevant diterpenoic resins, balsams and copals. Sample pre-treatment was limited to sonication in methanol at 55 degrees C for 30 min. This enables the identification of the resins in mixtures with other binders like plant gums, animal glues or drying oils, even when these media are present in excess. Colophony was identified as resinous constituent of a modelling mass for gilded frames originating from the 19th century.

An evaluation of GC-MS and HPLC-FD methods for analysis of protein binders in paintings

Two chromatographic methods have been compared for analysis of protein-binding media used in paintings, namely, HPLC with fluorescence detection and GC-MS. The proteins were hydrolyzed to the corresponding amino acids (AAs) by gaseous HCl and the AAs were derivatized with methyl chloroformate, followed by GC-MS or by HPLC after derivatization with the AccQ fluorescence reagent. The hydrolysis, derivatization reactions and the chromatographic procedures have been optimized and applied to standard binding media, model and real samples of paintings. The methods have been compared and critically evaluated.