DART-MS for rapid identification of logwood (Hematoxylum campechianum) dye in textile fibers: Effects of yarn composition and mordants

Document Type

Book Chapter

Publication Date

2023

Department/School

Chemistry

Publication Title

Chemistry in the Service of Archaeology

Abstract

Logwood dye, obtained from the heartwood of the Hematoxylum campechianum tree, produces a rainbow of purples, blues, and blacks when used with metal mordants on cotton, wool, and silk. This broad variety of colors made it a popular choice as a textile dye in Europe by the 18th century. Identifying logwood in historic textiles is often difficult; the most common extraction procedures used result in low signal by HPLC with absorbance detection, primarily due to decomposition and oxidation of the main colorant molecule, hematoxylin. Ambient ionization mass spectrometry has many advantages over HPLC for identification of dyes in minute samples of historic textiles. Direct analysis in real time (DART) mass spectrometry indicates the presence of hematoxylin and its derivatives in reference samples prepared with logwood on proteinaceous fibers like wool and silk in just a few seconds of analysis time. Adding a few microliters of concentrated formic acid to fibers immediately before introducing them into the ion source results in stronger signals from the proteinaceous fibers and makes possible the identification of logwood on cotton as well. The signal intensity for these species is also related to the metal salt used as a mordant. We report here on our DART-MS characterization of logwood dyes in a reference collection to better understand how the mordants and fiber composition may influence our ability to identify logwood in historic textiles.

Comments

R. A. Armitage is a faculty member in EMU's Department of Chemistry.

*T. Fairchild is an EMU student.

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