Investigation of natural dyes in 15th c. documents seal threads from the Romanian Academy Library, by LC-DAD-MS (triple quadrupole)

Dyes and biological sources in 40 samples from red seal threads in 38 documents issued by the Chancery of Moldavia between 1460 and 1503 were investigated by liquid chromatography with UV-Vis (DAD) and mass spectrometric (MS) detection. Lac dye (Kerria lacca Kerr), redwood type (Caesalpinia spp.) and madder (Rubia sp.), as individual dyes or in combinations, were responsible for the colour in all the dyed yarns while tannins were present in more than half of the total number of samples. The presence of major dyes, such as alizarin, purpurin, laccaic acid A and soluble redwood - a marker compound for Caesalpinia species were observed by both DAD and MS detectors while minor compounds (rubiadin, anthragallol, xanthopurpurin, munjistin, flavokermesic acid etc.) were only detected by mass spectrometry. Single stage MS detection was used in the Full Scan mode followed by data processing through Ion Extraction according to the molecular ions of compounds in the database. Tandem MS detection (MS2) was also achieved, through using the Product Ion Scan operating mode. Identification of dyes was made according to retention time, UV-Vis and MS data, based on information collected on standards - dyes and dyed fibers. The biological sources detected are discussed as compared with those identified in ecclesiastical embroideries from the same period, ordered by the same Prince, Stephan the Great (1457-1504).