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In this paper, partial least square (PLS) regression is innovatively applied for a semi-quantitative non invasive study of the most precious dye of Antiquity: Tyrian purple. This original approach for the study of organic dyes in the cultural heritage field, is based on the correlation of spectrophotometric (UV-Visible) and chromatographic (Fast-HT-HPLC-PDA) data from an extensive set of textiles prepared with different snail species according to historical recipes. A cross-validated PLS model, based on the quantity of 6,6'-dibromoindigotin, displays an excellent correlation factor (R(2)Y = 0.987) between values determined by chromatography and those predicted from reflectance spectra. This indicates that the spectral features of Tyrian purple on textile fibre is strictly related to the amount of this indigoid component whose content may be non invasively predicted from reflectance spectrum. The studied correlation also highlights that, independently of the dyeing method and nature of the textile fibre used, the relative content of 6,6'-dibromindigotin may be used as a parameter to distinguish samples prepared with Hexaplex trunculus L. snails from those prepared with further mollusc species. To validate this model, archaeological textile fragments dating from the Roman period were successfully examined. The results achieved open an absolutely new way in Tyrian purple analysis in cultural heritage by non invasive spectroscopic techniques attesting their convergence with HPLC and giving them a semi-quantitative value., (Copyright © 2016 Elsevier B.V. All rights reserved.)

CE with UV-Vis and MS detections was investigated as a technique for detection of main components of selected natural dyes of plant and insect origin. The BGE giving the best separation of the investigated flavonoids and anthraquinoids, suitable for MS detection consisted of 40 mM ammonium acetate solution of pH 9.5 with 40% ACN. LODs obtained with MS detection were even one order of magnitude lower than the ones obtained with UV-Vis detection. Application of MS detection enabled determination of eleven dye compounds from three different chemical groups in 15 min. and proved to be more satisfactory than diode-array detection in the electrophoretic analysis of main classes of natural dyes both in terms of selectivity and sensitivity of analysis.

LC with MS detection was optimized for sensitive and selective analysis of main classes of natural dyes used in ancient times for dyeing textiles -- red anthraquinoids, yellow flavonoids, and known degradation products of flavonols -- hydroxybenzoic acids. Fragmentation patterns of both negative and positive molecular ions for the above mentioned compounds were investigated. Three acquisition modes of MS analysis: scanning, SIM, and multiple reaction monitoring (MRM) in both positive and negative ion modes were optimized and compared with each other and with the UV-Vis diode-array detection. Even though in the applied chromatographic system formic acid was used in the mobile phase, SIM in the negative ion mode was the most selective and sensitive detection for all the investigated compounds when both mixtures of standards and analysis of extracts from archeological samples were concerned, with one exception -- alizarin, for which MS detection in positive ion mode was more sensitive. Detection limits obtained with MS detection for all investigated compounds except quinizarin were lower than the ones obtained with the diode-array UV-Vis detection, making MS detection the most suitable tool for the analysis of natural dyes and their degradation products in extracts from archeological samples.

Textiles excavated from Scottish sites belonging now to the collections of the National Museums of Scotland, including seventeenth century textiles from peat bogs in the Scottish Highlands and Islands, were selected for analysis by high performance liquid chromatography with photodiode array detection (PDA HPLC) to detect whether any dyes remained and, if so, to identify their biological sources. Dye components were identified in 36 of the 81 samples analysed. Although it was not possible to identify the exact sources of the dyestuffs because of the wide-spread occurrence of these natural dyes components, the study has shown that textiles previously not thought to have been coloured had detectable traces of dye. Before the historical textiles were analyzed, an improved extraction procedure that combined the routine acid hydrolysis method with one using dimethylformamide (DMF) was applied. The DMF method enabled increased recovery of major flavonoid and anthraquinoid compounds, and very high efficiency of recovery of indigotin even in textiles with no colour visible, thereby complementing the acid hydrolysis method already in use. Extracts from historical thread samples were analysed by PDA HPLC using a reversed-phase gradient system comprising of a C18 column (150 mm x 4.6 mm i.d., 25 +/- 1 degrees C) with water, methanol and o-phosphoric acid at an eluent flow rate of 1.2 ml/min. A preliminary investigation to improve the detection limits further for a selection of natural dyes was made by comparing results from the 4.6mm internal diameter (i.d.) column with a narrow bore C18 column (2.1 mm i.d.). An increase in the detector response was observed for narrow-bore column proving its possibility of enhancement of sensitivity.

The paper describes a high performance liquid chromatography-UV/Vis spectrometry detection analytical approach to the identification of some redwood species of historical importance in textile dyeing. The group of extracted dyestuffs considered as "insoluble" because of their non-aqueous or alkaline extraction conditions is present in the wood of the Pterocarpus family and Baphia nitida species. First, the crude extracts of tinctorial and related species and their chromatographic fingerprints were studied. This part of work shows that some species not yet mentioned in the literature have potential dyeing properties. Subsequent experiments performed on the redwood cargo of a 200-year-old archaeological shipwreck allowed identification of the water-logged wood species. Furthermore, the different methods of dyestuff extraction used for dyeing according to traditional recipes and their impact on analytical results were studied. They show that standard recovery obtained by acid hydrolysis of dyestuff from dyed yarns is inadequate. Hence, alternative solvent-based procedures were proposed. The identification of species in textile threads then becomes possible. The applied approach was validated by analysis of dyed reference yarns with some indications of crude material extraction mode. The employed method of analysis seems to be useful for "insoluble" wood species identification in cultural heritage artifacts as well as for phytochemical purposes, despite the fact that very few detected color compounds were chemically identified.

Liquid chromatography (LC) combined with ultraviolet-visible (UV-Vis) and mass spectrometric (MS) detection was utilized to study the chemical components present in extracts of natural dyes originating from fiber samples obtained from Coptic textiles from Early Christian Art Collection of National Museum in Warsaw. Chromatographic retention, ionization, UV-Vis and mass spectra of twenty selected dye compounds of flavanoid-, anthraquinone- and indigo-types were studied. Most of the investigated compounds could be ionized by positive and negative ion electrospray ionization. Difficulties with the ionization by electrospray were experienced for indigotin and brominated indigotins, but these were ionized by atmospheric pressure chemical ionization. Mass spectrometric detection, utilizing different scanning modes of a triple quadrupole mass spectrometer, combined with the UV-Vis detection was demonstrated to be a powerful approach to detection and identification of dyes in the extracts of archeological textiles. Using this approach the following compounds were identified in the extracts of Coptic textiles: luteolin, apigenin, rhamnetin, kaempferol, alizarin, purpurin, xanthopurpurin, monochloroalizarin, indirubin, and so the type of dye that was utilized to dye the textiles could be identified. Detection capabilities for several dye-type analytes were compared for the UV-Vis and mass spectrometric detection. The signal-to-noise ratios obtained for luteolin, apigenin, and rhamnetin were higher for the MS detection for most of the examined sample extracts. Purpurin, alizarin, and indirubin showed similar signal-to-noise ratios for UV-Vis and mass spectrometric detection.

Reversed-phase HPLC with diode-array UV-Vis spectrophotometric detection has been used for identification of natural dyes in extracts from wool and silk fibres from archeological textiles. The examined objects originate from 4th to 12th Century Egypt and belong to the collection of Early Christian Art of the National Museum in Warsaw. Extraction from fibres was carried out with HCl solution containing ethanol or with warm pyridine. As the main individual chemical components of natural dyes, anthraquinone, indigoid and flavonoid dyes including alizarin, purpurin, luteolin, apigenin, carminic acid, ellagic acid, gallic acid, laccaic acids A and B and indigotin were found. For pyridine extracts another mobile phase with an optimized gradient of organic modifier concentration was used. With such an eluent the appearance of double peaks for indigotin and indirubin was eliminated. For acidic extraction of dyes from fibres, ethanol was used. Due to its higher boiling point than methanol it evaporates slower from the extraction solution enabling a more efficient extraction of dyes.