文物蛋白胶料的气相色谱-质谱分析方法探讨

Methodological Study of Proteinaceous Binders in Artworks by GC-MS

为了探讨文物蛋白胶结材料的气相色谱-质谱(GC-MS)分析方法,以正亮氨酸为内标,N-(叔丁基二甲硅烷基)-N-甲基三氟乙酰胺(简称MTBSTFA)+1%特丁基二甲基氯代硅烷作为衍生化试剂,建立了蛋白胶料中常见的丙氨酸、甘氨酸等11种氨基酸的标准曲线,测定了每种氨基酸的精密度和检出限,并将该方法用于现代参考胶料和文物样品的分析测量。结果表明,GC-MS法对氨基酸的分离效果较好,除羟脯氨酸的稳定性略差外,其余10种氨基酸标准曲线的相关系数(R)均大于0.99,11种氨基酸的相对标准偏差(RSD)为2.7%~6.3%。甘氨酸的检出限最低,为0.066μg/g;亮氨酸的检出限最高,为0.676μg/g。在对猪皮胶、全蛋和牛奶3种现代参考胶料氨基酸分析的基础上,结合主成分分析(PCA)法揭示了3种胶料的特征性,并采用该方法鉴定了广西服饰金线文物样品中的蛋白胶料,表明该方法适用于文物蛋白胶料的定量分析。

Being one of the most important parts of polychrome cultural relics, a binder is used as an adhesive of pigments, but it is closely related to various kinds of cultural relic diseases. Recently, there are some reports on analyses of binders in artworks, such as egg, animal glues, milk(casein), plant waxes, oils, resins, polysaccharide materials and so on. However, methodological study of proteinaceous binders in artworks by gas chromatography-mass spectrometry(GC-MS) is rarely reported. In this study, a method of GC-MS was developed for identification of proteinaceous binders in artworks depending on determination of the eleven common amino acids(alanine, glycine, valine, leucine, isoleucine, serine, proline, phenylalanine, aspartic acid, glutamic acid and hydroxyproline). The mainly analytical procedure was as follows: 1) extraction by ammonia with an ultrasonic cleaner;2) enrichment and purification by a C4 solid phase extraction column;3) digestion to amino acids in a microwave oven with 6 mol/L HCl;4) derivatization by using N-tert-butyldimethylsilyl-N-methyltrifluoroacetamide(MTBSTFA) with 1% tert-butyldimethylchlorosilane as a derivatization reagent;5) analyses by a 7890 A-5975 C GC-MS(Agilent, USA) with norleucine as the internal standard. The results showed that they had good linear relationships with the linear correlation coefficients(R) of no less than 0.99, and the limits of detection of the amino acids ranged from 0.066 to 0.676 μg/g. The relative standard deviations(RSDs) were from 2.7% to 6.3% of 11 kinds of mixed standard solutions(n=6), and RSDs were below 5% excepting for that of serine and hydroxyproline. Based on the analyses of three kinds of modern reference samples(pigskin glue, egg and milk), the results showed that each binder was characterized by a specific set of amino acid percentages, which could be used as a "fingerprint". Animal glue binder contains hydroxyproline(Hyp) as a special amino acid and has high percentage of glycine(Gly). Egg binder has high percentages of aspartic acid(Asp) and serine(Ser), while milk has high percentage of glutamic acid(Glu). Moreover, based on combination of principal component analysis(PCA), the proteinaceous binders in the golden wire of Guangxi clothing were identified as mixture glues consisting of animal glue and egg. From experimental results it has been proved that GC-MS is suitable for quantitative analysis of proteinaceous binders in artworks.