Zastosowanie chromatografii w połączeniu ze spektrometrią masową (GC-MS) do analizy spoiw stosowanych w malarstwie

An analysis of bindings used in painting, polychromy sculpture and illuminated manuscripts is one of the most difficult problems in the conservation of historical monuments. Undoubtedly, this situation is connected with the application for bindings of mixtures of compounds of natural origin with assorted functional groups which are always a mixture of individual chemicals. The identification of those components is time-consuming and complex because it calls for the transition of multi-molecule compounds into simple substances, well-know and easily analysed. Literature data confirmed that the best analytical method of composite mixtures is gas chromatography combined with mass spectrometry since the former, which makes use of capillary columns, makes it possible to divide mixtures containing even hundreds of individual chemicals into components, while the mass spectrometer which registers the spectrum, allows unambiguous identification of the compound. This is the reason why precisely this method was chosen for an analysis of bindings as most precise and effective. It requires, however, a suitable preparation of a sample for subsequent examination. Due to the fact that compounds used as binding material belong to different classes of organic compounds and are frequently applied in painting technique alongside each other, it was necessary to discover the universal analysis procedure, effective for all potential components of the binding. A sample of the painting layer is subjected to hydrolysis and then derivatisation, in other words,volatile or less volatile products of hydrolysis are transformed into easily analysed derivatives. A comparison of the outcome of chromatographic analyses of the examined material with analyses of known bindings makes it possible to identify components. Part of the sample is subjected to acid hydrolysis with a suitable mixture of acids, which causes a hydrolysis of all components of the binding. After the removal of acids and water as well as silification, the components can be identified as trimethylsilite derivatives. The remaining part of the sample is subjected to alkaline hydrolysis by means of a methanol solution of tetramethylene ammonium or trimethylene aryl ammonium. The hydrolyzate prepared in this way allows us to identify independently various types of organic and non-organic acids as methyl esters. The application of gas chromatography and mass spectroscopy (GC-MS) for analysing bindings facilitates the identification of all the components of the bindings and a quantitative assessment of the contents of particular components.