Figure 1
From: Mapping Natural Dyes in Archeological Textiles by Imaging Mass Spectrometry
MALDI-TOF-MS spectra of (a) an authentic indigo reference and (b) blue-colored historic fibers (sample ID VA57042). Measurements were carried out with the assistance of Universal MALDI matrix in reflector positive mode. Indigo-type dyestuffs were detected as radical cation [M]•+ (m/z 262) and protonated ion [M + H]+ (m/z 263). Note: Besides these signals, a mass peak at m/z 264 was detected. A similar signal was also observed in positive ion MALDI-TOF-MS and TOF-SIMS spectra of indigo by Xu et al.41 and Lee et al.42. Presumably, it is a product of a redox reaction ([M + 2H]•+ as putative species, compare43,44).
