HPLC-DAD-MS analysis of colorant and resinous components of lac-dye: A comparison between Kerria and Paratachardina genera

A database using high performance liquid chromatography with diode array detection was created for lac-dye insects (Kerria and Paratachardina genera) in order to identify the red dye used in historical textiles. Lac from Kerria and Paratachardina species was easily distinguished by liquid chromatography coupled to negative electrospray ionization tandem mass spectrometry. Seventy-six historical lac-dye specimens and seven reference insect specimens were analyzed and compared with 41 historical carpet samples. Using this approach, the presence of Kerria spp. was identified in three carpets, pointing to an Iranian provenance and corroborating a 16th/17th-century date for them, obtained previously with C14 analysis. Multivariate data analysis was applied to differentiate sources of Kerria and improve the lac-dye database. PCA indicates that discrimination can be obtained according to composition. Information regarding pigment and resin concentrations is recovered separately in first and second principal components, respectively, which offers a basis of separation for this type of data. The development of this lac-dye database is an important step towards improving research on lac-dye species, which can contribute to more accurate identification of the provenance of historical textiles. This work reinforces the importance of using taxonomically-verified specimens of Kerria, previously submitted to molecular taxonomic studies, to construct a more reliable lac-dye database capable of identifying the lac species present in historical textiles, as well as the provenance of the insect used.