Application of DESI–MS for dye analysis of historical textiles

One key issue in the dye analysis field is the need to sample culturally significant objects. This issue is amplified when working with more fragile objects, such as historical textiles, where sampling is often impossible without threatening the structural integrity of the object. To circumvent the impact of dye analysis, micro-invasive or non-invasive analytical approaches have been recently developed to the study of museum collections (Tamburini and Dyer, 2019; Sandström et al., 2021; Chavanne et al., 2022). However, the application of non-invasive techniques, such as fibre optic reflectance spectroscopy (FORS), still requires significant modelling for data interpretation due to the complexity of dyestuff mixtures (Chavanne et al., 2022).Mass spectrometry is one of the main techniques used in heritage science due to its high sensitivity and selectivity, but its use is still restricted by the sampling requirement. The development of ambient mass spectrometry techniques, such as direct analysis in real time mass spectrometry (DART-MS) and desorption electrospray ionisation mass spectrometry (DESI-MS) (Takáts et al., 2004), bypass the need for sampling, enabling the analysis of hitherto inaccessible objects, without reducing the information gained from the analysis. Although DART-MS has successfully been applied for dye analysis (Selvius DeRoo and Armitage, 2011; Armitage et al., 2019), DESI-MS was only recently developed for the study of ink in historical manuscripts (Newton, 2019) and is yet to be fully introduced for the analysis of dyes in historical textiles. A DESI source was built and optimised for dye analysis at the University of Edinburgh. The source has the sprayer holder mounted onto positioners for manual control of the x-, y- and z-axes and a rotation mount for manual adjustment of the sprayer angle. A Bruker 7T SolariX FT-ICR-MS was used for all analyses. Initial testing and optimisation were undertaken on silk, wool and cellulosic samples dyed with a range of natural and early synthetic dyes. The versatility of the DESI technique was tested on a variety of objects, including embroidery samplers from 1800–1838 and a reference book by the dye chemist Adolf Lehne dated to 1893. Overall, the project has demonstrated the applicability of DESI-MS for dye analysis of historical textiles.