Wspólnotowy Serwis Informacyjny Badan i Rozwoju - CORDIS

Identification of neoflavonoid dyes by PDA HPLC after acid extraction

The red dye, brazilwood (Caesalpinia spp.) and black dye, logwood (Haematoxylum campechianum) contains the neoflavonoids brasilein and haematein respectively. These have proved difficult to identify conclusively in historical yarn samples because the routine extraction method for preparing samples for PDA HPLC analysis, involving acid hydrolysis, alters the main colouring component. The chemical structure and properties of these altered components, detectable by PDA HPLC, was unknown.

The effect of the extraction process on both brazilwood and logwood (included in the study because it contains a structurally-related neoflavonoid compound, haematein, and was available in the historical period for the tapestries being researched) had to be established before analysing model and historical samples.

Studies with UV-visible spectrometry and PDA HPLC on pure standards and dye extracts confirmed that haematein and brasilein were both acid sensitive. Hematein was found to form reaction products, which gave reproducible chromatographic and spectral results. Following molecular structure elucidation studies by the UoE, the logwood marker compound was identified, giving confidence to PDA HPLC analysis results for the historical tapestry samples. The molecular structure for the brasilein-derived product was not possible to elucidate. However, the UoE was able to demonstrate that a second, uncoloured component in brazilwood dye extracts was consistent and reproducible, thus enabling it to be used as a reliable marker for this dye source in the PDA HPLC analysis of historical samples.

Reported by

National Museums of Scotland
Royal Museum of Scotland Chambers Street
EH1 1JF Edinburgh
United Kingdom
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