From Plant Extracts to Historical Textiles: Characterization of Dyestuffs by GC-MS

A gas chromatographic-mass spectrometric procedure for the analysis of dyes from plant extracts was optimized and applied for the detection of components in extracts from 12 dyeing plants native from all over the world. The main marker molecules in each of the dyestuffs, as well as accessory compounds, were successfully separated and identified by means of their electron impact mass spectra, thus demonstrating that a single GC-MS procedure can be conveniently applied to the detection of natural dyes such as flavonoids, neoflavonoids, anthraquinones and tannins. Other constituents of plant extracts, such as organic acids, oils and sugars, that hydrolyse during the extraction process, were also detected and recognized in the same chromatographic run. The GC-MS method was tested on woollen references dyed according to traditional recipes, and on historical wool samples taken from a tapestry of the sixteenth century, and the main dyestuffs used for colouring could be traced even with the low amounts usually available with the archaeometric samples. Besides some limitations, that are addressed, the results show that the GC analysis is a useful tool for quick assessment and control of natural extracts and the application of the technique for the characterization of dyes in historical textiles, in addition or in place of the more widely used procedures that employ liquid chromatography, is encouraged.