Characterization of Dye Extracts from Historical Cultural-Heritage Objects Using State-of-the-Art Comprehensive Two-Dimensional Liquid Chromatography and Mass Spectrometry with Active Modulation and Optimized Shifting Gradients

Abstract

Unbiased characterization of dyes and their degradation products in cultural-heritage objects requires an analytical method which provides universal separation power regardless of dye classes. Dyes are small molecules that vary widely in chemical structure and properties, which renders their characterization by a single method challenging. We have developed a comprehensive two-dimensional liquid chromatography method hyphenated with mass spectrometry and UV–vis detection. We use stationary-phase-assisted modulation to enhance the method in terms of detection limits and solvent compatibility and to reduce the analysis time. The PIOTR program was used to optimize an assembly of shifting second-dimension gradients, which resulted in a high degree of orthogonality (80% in terms of the asterisk concept). The resulting method is universally applicable to all classes of dyes extracted from cultural-heritage objects. Thanks to the high peak capacity and orthogonality, dye components can be separated from chemically similar impurities and degradation products, providing a detailed fingerprint of the dyes mixture in a specific sample. The method was applied to a number of challenging dye extracts from 17th- and 19th-century cultural-heritage objects.

Exploring the transition from natural to synthetic dyes in the production of 19th-century Central Asian ikat textiles

“…42000), was identified based on the presence of its main component (λ max = 622 nm; [M+H] + at m/z 329) and a series of mono-demethylated (λ max = 608 nm; [M+H] + at m/z 315), bis-demethylated (λ max = 594 nm; [M+H] + at m/z 301) and tri-demethylated (λ max = 580 nm; [M+H] + at m/z 287) derivatives (Fig. 5), in agreement with literature data [38,63,64]. Several isomers were detected, corresponding to different demethylated positions.…”

“…7). These observations were again in agreement with previous works on the characterization of methyl violet [44,63], although the lack of tandem mass spectrometry detection did not allow us to precisely assign the various isomers. (Fig.…”

“…42510) and the identification was based on the presence of three compounds, respectively corresponding to the fuchsine molecule, also referred to as rosaniline or Magenta I, (λ max = 546 nm; [M+H] + at m/z 302) and the homologues with one additional methyl group (Magenta II; λ max = 548 nm; [M+H] + at m/z 316) and two additional methyl groups on the aromatic rings (Magenta III, λ max = 550 nm; [M+H] + at m/z 330) ( Fig. 6), also in agreement with published data [38,44,63,64].…”

“…In a blue sample from S2004.79, in addition to indigoids, one molecule was detected, whose UV-Vis spectrum (λ max = 444 nm) and retention time were similar to (but not perfectly matched) the reference of the azo dye orange IV (acid orange 5, C.I. 13080) [63,64]. The mass of the pseudomolecular ion or any other ion related to the molecule were not detected.…”

“…For both HPLC-DAD and HPLC-DAD-MS analysis, dye components were associated with natural and synthetic dye sources using data measured from reference materials (retention times, UV-Vis spectra and mass measurements) made available by the Getty Conservation Institute (Los Angeles, USA) [61], as well as from the published literature [14,23,24,27,37,38,40,44,[62][63][64]. The dates reported are those attributed based on stylistic interpretation, except for the ikats in which synthetic dyes were found (terminus post quem production dates are reported in bold for these textiles).…”