Department of IPM Chemistry and NIS-Centre of Excellence, University of Turin, Via Pietro Giuria n degrees 7, 10125 Torino, Italy.
Anal Bioanal Chem. 2010 Feb;396(4):1559-69. doi: 10.1007/s00216-009-3325-4. Epub 2009 Dec 13.
Plant gums are present in works of art as binding media for watercolours and adhesives for cellulosic substrates. Thermally assisted hydrolysis and methylation (THM) in combination with analytical pyrolysis coupled to GC/MS has been applied to the characterisation of plant gums typically used in artworks. THM products from standard samples of arabic gum, tragacanth gum and cherry gum were characterised. The main products identified are permethylated and partially methylated aldonic acids, characteristic of specific epimeric sugars. Aldonic acids were formed by alkaline hydrolysis of free reducing sugars and of reducing polysaccharide terminal groups, while methylation occurs during pyrolysis. The presence of these characteristic markers allows gum identification. A systematic analysis of all the parameters that can affect the marker yields was performed. In particular, the influence of pyrolysis temperature, reagent concentration and contact time between tetramethylammonium hydroxide and sample were studied, and different kinds of sample preparation procedures were tested. Some analyses on real watercolours were performed, and gum binders were classified using the peak area ratio of the main monosaccharide markers.
植物胶作为水彩画的黏合剂和纤维素基底的黏合剂存在于艺术品中。热辅助水解和甲基化（THM）与分析性热解相结合，与 GC/MS 耦联，已应用于通常用于艺术品中的植物胶的特征描述。对阿拉伯胶、黄蓍胶和樱桃胶的标准样品的 THM 产物进行了特征描述。鉴定出的主要产物是经 permethylation 和部分 methylation 的 aldonic 酸，这是特定差向异构体糖的特征。aldonic 酸是通过游离还原糖和还原多糖末端基团的碱性水解形成的，而甲基化发生在热解过程中。这些特征标记物的存在允许对胶进行鉴定。系统地分析了可能影响标记物产率的所有参数。特别是研究了热解温度、试剂浓度以及四甲基氢氧化铵与样品之间的接触时间的影响，并测试了不同种类的样品制备程序。对一些实际的水彩画进行了分析，并使用主要单糖标记物的峰面积比对胶黏剂进行了分类。
