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Chapter 4
Developing Direct Analysis in Real Time Time-of-Flight Mass Spectrometric Methods for Identification of Organic Dyes in Historic Wool Textiles Calvin J. Day,1 Cathy Selvius DeRoo,2 and Ruth Ann Armitage*,1 1Department
of Chemistry, Eastern Michigan University, Ypsilanti, Michigan 48197 2Conservation Department, Detroit Institute of Arts, Detroit, Michigan 48202 *E-mail:
[email protected] Identifying organic dye compounds in textiles is a significant challenge in conservation science. Existing methods, such as liquid chromatography, require lengthy sample preparation procedures that can induce structural changes in the extracted colorants. Direct analysis in real time mass spectrometry is a simple method for identifying a number of classes of dye compounds in single fibers. Blue and red fibers from historic tapestries from the Detroit Institute of Arts collections yielded clear spectra for indigotin and several anthraquinones including alizarin and purpurin, indicating the use of indigo and madder as sources of the colorants. Flavonoid dyes that impart yellow colors are generally considered more difficult to identify, as many of the colorant compounds are structural isomers.
Introduction Identification of organic dye sources in historic textiles is a significant problem in archaeological and conservation sciences. Derived from a wide array of plant, animal, lichen, and insect sources, organic dyes are identified not just © 2013 American Chemical Society In Archaeological Chemistry VIII; Armitage, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2013.
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by the presence of a single colorant molecule, but generally by the ratios in which multiple colorant compounds are present relative to one another. Typically, samples must be extracted with acid to separate the colorants from the fiber matrix prior to analysis with chromatographic methods. Extraction protocols are well known to induce hydrolysis in many of the colorant compounds (1, 2). High performance liquid chromatography is the most commonly applied technique, usually using either photodiode array UV-visible spectroscopic or electrospray ionization mass spectrometric detection (3–6). The destructive nature of these sample preparation methods, the complexity of the separation protocols, and the length of time required for chromatographic analyses suggest that there is need for simple and rapid methods for identification of organic dye sources in cultural heritage materials. Surface-enhanced resonance Raman spectroscopy is one possible alternative to HPLC for this application (7, 8). The necessity of preparing the nanoparticle substrates, however, is a significant limitation. For the past three years, the collaborative efforts of scientists at the DIA and Eastern Michigan University have led to new methods for direct analysis in real time ionization coupled to high-resolution time-of-flight mass spectrometry (DART-MS) for characterization of organic colorants directly from textile fibers. DART ionization (9) is ideal for direct identification of small (
