Comparison of extraction methods for the analysis of natural dyes in historical textiles by high-performance liquid chromatography |
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Authors: | Lemonia Valianou Ioannis Karapanagiotis Yannis Chryssoulakis |
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Institution: | (1) Ormylia Art Diagnosis Center, Ormylia, 63071, Chalkidiki, Greece;(2) School of Chemical Engineering, National Technical University of Athens, Athens, 15773, Greece; |
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Abstract: | Different methods for the extraction of Dactylopius coccus Costa, Rubia tinctorum L., Isatis tinctoria L., Reseda luteola L., Curcuma longa L. and Cotinus coggygria Scop. from wool fibres are investigated using high-performance liquid chromatography with diode array detector (HPLC-DAD).
The efficiencies of five extraction methods which include the use of HCl (widely used extraction method), citric acid, oxalic
acid, TFA and a combination of HCOOH and EDTA are compared on the basis of the (a) number, (b) relative quantities, measured
as HPLC peak areas and (c) signal-to-noise ratios (S/N) of the compounds extracted from the wool substrates. Flavonoid glycosides and curcuminoids contained in R. luteola L. and C. longa L., respectively, according to liquid chromatography with mass spectrometry (LC-MS) identifications, are not detected after
treating the fibres with HCl. All the other milder methods are successful in extracting these compounds. Experiments are performed
using HPLC-DAD to compare the HPLC peak areas and the S/N of the following extracted compounds: indigotin, indirubin, curcumin, demethoxycurcumin, bisdemethoxycurcumin, fisetin, sulfuretin,
luteolin, luteolin-7-O-glucoside, apigenin, carminic acid, alizarin, puruprin and rubiadin. It is shown that the TFA method provides overall the
best results as it gives elevated extraction yields except for fisetin, luteolin, apigenin and luteolin-7-O-glucoside and highest S/N except for fisetin and luteolin-7-O-glucoside. It is noteworthy that treatment of the fibres with the typical HCl extraction method results overall in very low
S/N. The TFA method is selected for further studies, as follows. First, it is applied on silk dyed samples and compared with
the HCl method. The same relative differences of the TFA and HCl methods observed for the wool dyed samples are reported for
the silk dyed samples too, except for rubiadin, luteolin and apigenin. Thus, in most cases, the nature of the substrate (wool
or silk) appears to have negligible effects on the relative difference of the two extraction methods. Second, the selected
TFA method is applied to treat wool and silk historical samples extracted from textiles of the Mamluk period, resulting in
the identification of several colouring compounds. In all extraction methods mentioned above, DMSO is used to dissolve the
dyes, after acid treatment. |
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