Organic paint constituents are very challenging from an analytical point of view, given the simultaneous presence of inorganic and organic natural and synthetic substances, ageing and degradation processes, and the very low amount of organic matter (a few percentage points in the overall weight or even lower) in the minute heterogeneous paint sample (<< 1 mg)
At present, the coupling of chromatography with mass spectrometry is the preferred analytical approach to characterize organic paint materials. The choice of GC and LC is driven by the fact that natural organic substances are complex mixtures of many chemical species, which are very similar to each other: the resolution and determination of the molecular profile are essential in order to identify the materials present and the ageing pathways. Consequently, in this specific field, the coupling of chromatography with mass spectrometry is necessary due to the high number of compounds with similar retention times. In addition, because the most significant compounds are not available as commercial standards, identification cannot be based only on retention times, and requires the confirmation of mass spectra.
Methodology for the analysis of binders and varnishes
In this research we use a gas chromatography/mass spectrometry (GC/MS) analytical procedure based on the multi-step chemical pre-treatment of the sample. This analytical procedure permits the simultaneous characterization of glycerolipids, natural waxes, proteinaceous, resinous and polysaccharide materials in the same micro sample from painted works of art, avoiding analytical interferences from pigments and difficulties arising when the sample must be divided into several different aliquots to be chemically processed separately, for the characterization of the various classes of organic materials.
Methodology for the analysis of dyes
Our methodology for the analysis of organic pigments is based on the extraction of the main coloring components from the samples, followed by the analysis via high performance liquid chromatography (HPLC), which enables the separation and subsequent identification of tens of dyes molecules from a small amount of sample (less than 0.1 mg). The detection of the separated compounds is based on the acquisition of their UV-Vis spectra (Diode Array Detector) or their mass spectra (ElectroSpray Ionisation – High Resolution Tandem Mass Spectrometer).
Methodology for the analysis of lipid-based binders
Reverse Phase HPLC with ESI-Q-ToF detector will be used to determine the glyceride profile of the lipid fraction of oil-based paints and possibly to characterize the reaction products deriving from the synthetic process employed to produce the artistic material. We will use HPLC-ESI-Q-ToF profiling to fully characterize historical and modern materials and to clarify their ageing pathways.
Moreover, we will apply mass spectrometric analysis by flow injection-ESI-Q-ToF (FIA-ESI-Q-ToF) to obtain a fast fingerprint of the glyceride fraction and possible additives.
A. Lluveras, I. Bonaduce, A. Andreotti, M. P. Colombini, A GC/MS analytical procedure for the characterization of glycerolipids, natural waxes, terpenoid resins, proteinaceous and polysaccharide materials in the same paint micro sample avoiding interferences from inorganic mediaAnalytical Chemistry, 81 (2010) 376-386.).
I. Degano, M. Biesaga, M.P. Colombini, M. Trojanowicz, Historical and archaeological textiles: an insight on degradation products of wool yarns, Journal of Chromatography A, 1218, 2011, pp. 5837-5847.
J. La Nasa, I. Degano, F. Modugno, M.P. Colombini, Alkyd paints in art: Characterization using integrated mass spectrometry, Analytica Chimica Acta, 797, 2013, pp. 64-80.