Capillary electrophoresis equipped with laser induced fluorescence: a novel technique for separation and identification of natural dyes from historical textiles

The aim of this research was to evaluate the feasibility of capillary electrophoresis in micellar electrokinetic mode (MEKC) equipped with laser induced fluorescence (LIF) as a novel technique to study dyes extracted from valuable textiles. CE identification of dyes requires extraction of dyes from the substrate, which is one of the most challenging aspects in conservation science. Therefore, developing a technique with minimum destructive effect on objects is favorable. The most important advantages of using LIF are the low detection limits and high sensitivity which allow for the separation of very small quantities of sample, which makes it suitable for working with historical objects. Feasibility studies were performed to explore separation properties of a small number of historical dyes (alizarin, purpurin, carmine and morin) using: different concentrations of modifiers and borate buffer at different pH values, and applied voltages. By manipulating separation parameters the optimum separation condition for a mixture of 10 dyes was defined as: under 22 kV, 20 mM borate buffer at pH = 8.5; 20 mM SDS with 5% acetonitrile. The separation of flavonols and purpurin using CE at pH>9.2 appeared to be complicated by reproducibility in peak height and peak shape of purpurin. In this study the poor peak reproducibility of CE separations was attributed to photochemical properties of dyes. The 1st order rate constants ( for the decomposition of purpurin and selected flavonol dyes were determined under different pH conditions, for purpurin at pH=9.0 under dark condition was The stability of these dyes was greatly affected by pH, a modest decrease in pH (pH = 8.5) improved the stability and peak reproducibility of these dyes. To extract dyes from textiles, the existing extraction methods with focus on Hanson solubility parameters were evaluated. It appeared that methanol was the most suitable solvent and the dyes in the following samples were extracted by methanol and identifi