Early synthetic dyes--a challenge for tandem mass spectrometry

Abstract

The present study concerns identification of early yellow synthetic dyes from silk fibers taken from the 1930 spring color palette of the Lyon Dyers' Guild (La Chambre Syndicale des Teinturiers). The identification was based mainly on the electrospray ionization tandem mass spectrometry spectra obtained in the positive and negative ion modes. This technique was combined with high-performance liquid chromatography, which enabled separation of the analyzed compounds. Spectra registered for each of the examined synthetic dye allowed identification of their lost fragments. Moreover, isotopic profiles and exact measurements of m/z by using time of flight analyzer made possible to evaluate their elemental composition. In consequence, all obtained data, including UV-vis spectra, allowed to reconstruct molecular structures of examined colorants. Due to the lack of standards, the identification of the dyes was based only on the registration of fragment and quasi-molecular ions, what is rather uncommon in such analysis and means groping for the correct structure rather than proving signal identity by comparison with standards. Depending on substituents present in dye molecules, the lost fragments of the examined compounds involved SO(2), NO(•), NO(2)(•), CH(4), C(2)H(4), C(2)H(5)(•), C(2)H(6), CH(2)=N-CH(3), (CH(3))(2)NH, CH(2)= NH, CH(3)-NH(2), as well as CO and CO(2). The performed study led to identification of various colorants: rhodamine 6 G, rhodamine B, malachite green, quinoline yellow, picric acid and acetoquinone yellow 5JZ.