Identification of natural indigo in historical textiles by GC–MS

Abstract

The possibility of successfully applying a common GC-MS procedure for identification in one step of all types of dyes from plants of unknown origin and from historical objects is particularly attractive due to the high separation efficiency of the capillary columns, the MS detection sensitivity and the reproducibility of results. In this work, GC-MS analysis, previously and successfully used for the characterization of anthraquinones, flavonoids and tannins from plant extracts and historical samples, has been tested on indigoid dyestuffs. An analytical procedure based on the silylating agent N,O-bis-(trimethylsilyl)trifluoroacetamide (BSTFA) with 1% trimethylchlorosilane (TMCS) was applied to pure molecules of indigotin and indirubin and to plant extracts of Indigofera tinctoria L. and Isatis tinctoria L. Preliminary tests have been done to establish the chromatographic conditions and the derivatization amounts most suitable for the simultaneous detection of indigoid molecules and of the other natural compounds, such as fatty acids, carboxylic acids and sugars, contained within the plant extracts. In order to assess the capacity and the sensitivity of the analytical procedure in typical archaeometric applications, wool samples dyed in the laboratory with indigo were analysed by mimicking the sample amounts typically available with historical objects. The electron ionization (EI) spectra of the main silylated derivatives of indigoid molecules obtained in this way constitute the necessary data set for the characterization of natural extracts and historical works of art. Subsequently, the procedure has been applied to historical samples for the detection of indigo and of other dyestuffs eventually contained in samples. Additional information, useful for restoration and preservation of works of art, could be also obtained on the nature of stains and smudges present on the sampled textile material. The GC-MS method turns out to be an efficient and fast analytical tool also for the identification of natural indigo in plants and textile artefacts, providing results complementary to those from high-performance liquid chromatography (HPLC).

Molecular Structures and Spectral Properties of Natural Indigo and Indirubin: Experimental and DFT Studies

“…Previous works on indigo mainly focused on the dyeing process optimization and ancient textile identification [7,8,9]. In order to improve the dyeing performance of indigo and expand its application in electronics and other fields, considerable research efforts have been devoted to the DFT studies of indigo and its derivatives [10,11,12,13,14].…”

Perception of Everyday Sounds: A Developmental Study of a Free Sorting Task

“…As the participants progressed in the task, they used internal representations of the classes that they had previously built to remember the sounds that constitute them. The binary association, which may be induced by the initial stimuli choice, allows a one-to-one comparison between two elements, which is easier than a multiple comparison of several elements [ 63 , 80 ].…”

From natural dye to herbal medicine: a systematic review of chemical constituents, pharmacological effects and clinical applications of indigo naturalis

“…The inorganic ingredients of indigo naturalis was consist of 70% calcium carbonate, 10% silica dioxide and calcium hydroxide [ 3 , 11 ]. In addition, it may also include Fe 2 (CO 3 ) 3 , Al 2 (CO 3 ) 3 , etc [ 11 ]. Calcium carbonate and calcium hydroxide are derived from lime, and silica dioxide and other impurities are derived from soil.…”

“…Besides TLC and HPLC, there are many other quality control methods for indigo naturalis. Degani et al [ 11 ] describe an analytical procedure based on the silylating agent N,O-bis-(trimethylsilyl) trifluoroacetamide with 1% trimethylchlorosilane for pure molecules of indigo, indirubin and plant extracts of indigo naturalis. Gas Chromatography–mass spectrometry turns out to be an efficient and fast analytical tool for the identification of natural indigo in plants and textile artifacts.…”