| Abstract: | SUMMARIES. This work aimed to identify natural dyes in extracts from Coptic fibres. The objects examined originate from fourth- to twelfth-century AD Egypt Chromatographic separations of all the samples were carried out using reversed-phase HPLC (high performance liquid chromatography) with UV-Vis detection and fluorescence detection. Fluorescence detection proved to be better than UV-Vis diode array detection for the determination of some compounds. Selected samples were analysed with HPLC-MS (HPLC-mass spectroscopy) which confirmed the LC-UV findings and allowed the detection and identification of additional compounds. Most of the dyes mentioned in the literature as having been used by Copts were detected: Armenian cochineal, flavouoid yellow dyes, indigotin, lac dye, madder and tannins. Some new compositions of significant colours were also discovered, which had not been reported previously in Coptic textiles. Elemental analysis using SEM-EDS (scanning electron microscopy energy dispersive spectroscopy) was performed to identify mordants.
CONCLUSION. HPLC with different detectors is a powerful method for the identification of dyes. Fluorescence detection with Ga(III) solution as post-column reagent proved to be more sensitive than UV-Vis detection for purpurin. rhamnetin, quercetin, gallic acid, kaempferol and munjistin. However, UV-Vis diode array detection was more sensitive for the determination of carminic and ellagic acids, luteolin, alizarin, apigenin, lawsone and indigoid dyes. In the case of the samples investigated, the detection capability of LC-MS was competitive with those observed for UV-Vis and fluorescence detection and advantageous for luteolin, apigenin and indirubin. Hence, these three detection methods used with HPLC separation should be considered as complementary for the determination of dyes in extracts from archaeological samples. Most of the dyes reported earlier in the literature to be used by Copts were detected in the extracts investigated. Additional components of some colours were discovered, mainly because of very low detection limits obtained for flavonols with fluorometric detection. Using LC-MS analysis, monochloroalizarin and dichloroalizarin were identified in one sample and xanthopurpurin in some samples of fibres from Coptic textiles. FTIR microscopy did not provide any information about dyes on archaeological threads because of the presence of strong signals from wool. High amounts of some elements were detected on the Coptic threads investigated by SEM-EDS. Tin, whose salts were used as mordants in ancient Egypt, was not found, but chromium together with copper was identified on one sample. However, results of elemental analysis can only be properly interpreted when combined with other chemical, historical and archaeological data. |
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