Identification of proteinaceous binding media of easel paintings by gas chromatography of the amino acid derivatives after catalytic hydrolysis by a protonated cation exchanger

Characterisation of standard tempera painting layers containing proteinaceous binders by pyrolysis (/methylation)-gas chromatography-mass spectrometry

“…Characterisation of proteinaceous binders by means of chromatographic techniques has been recently reviewed [2]. The identification is commonly carried out by determining the amino acid composition of the binding media using gas chromatography (GC) [3,4] or high-performance liquid chromatography (HPLC) [5,6] of pretreated samples. The principal disadvantages of these methods are related to the need of timeconsuming chemical steps (hydrolysis, extraction, derivatization) which can cause loss of amino acids.…”

GC/MS in the Characterisation of Protein Paint Binders

“…A decrease of the total recovery of proteins from tempera layers has been correlated with the presence of inorganic cations [11][12][13][14][15][16] that may reduce the solubility of the organic materials due to cross-linking reactions where cations may be active as catalysers.…”

“…The range of chromatographic techniques applied to the characterisation of the proteinaceous constituents in paint includes paper chromatography [32,33], thin-layer chromatography (TLC) [34][35][36], ionic exchange chromatography [37,38], reversed phase high-performance liquid chromatography with pre-column derivatisation [14,[39][40][41][42][43][44][45], gas chromatography [7,15,16,30,[46][47][48][49][50][51][52][53][54][55][56][57], and pyrolysis combined with gas chromatography-mass spectrometry (Py-GC/MS) [58][59][60][61][62][63][64][65][66]. Gas chromatography (GC) and gas chromatography-mass spectrometry (GC/MS) are among the most commonly used techniques for the identification of proteinaceous paint media, and they generally give more accurate and reliable results than other methods due to their high specificity and sensitivity [5,11,67].…”

“…This often leads to the formation of humins at the expense of amino acid content. A method has been suggested in the literature [16,55] to overcome this type of interference. It relies on a mild hydrolysis, performed under vacuum at 110°C for 24 h, in the presence of a strongly acidic ion exchange resin (suspended in water/ethanol solution) that acts as a catalyser.…”

“…The above-mentioned interactions with cations may selectively subtract some amino acids from the analysis or give rise to interferences during the analytical pretreatment and thus may hamper the correct identification of the proteinaceous binder [7]. In fact, a decrease in the total recovery of proteins from paint layers has been related to the presence of these inorganic cations and this may be due to the reduced solubility of the organic materials because of cross-linking reactions where cations may be active as catalysers or the formation of stable complexes with the amino acids [11][12][13][14][15][16]. It has been reported that the recovery of egg protein significantly decreases when gypsum, calcium oxalate or both are present [80].…”