Development of new extraction methods for analysis of natural and synthetic organic colourants from historical and artistic matrices

Abstract

Abstract: In this thesis, an innovative approach for the extraction and clean-up of natural and synthetic textile dyes based on a recently developed ammonia extraction protocol and a novel Dispersive Liquid-Liquid Microextraction (DLLME) is presented. The thesis builds upon recent research highlighting the benefits of the ammonia-based extraction protocol for efficient extraction and preservation of the glycosyl moieties present in some types of natural dyes. This state-of-the-art extraction technique requires the use of a clean-up step to purify and preconcentrate the dye molecules for analysis. This clean-up step has never before been investigated or developed, and current methods rely upon traditional Liquid-Liquid Extractions (LLE), which are not well suited to the very small quantities of materials available for the analysis of artefacts of cultural heritage. The novel DLLME protocol presented by this thesis was developed in order to improve the recovery of natural dyes for analysis, and is also the first clean-up protocol to be developed for the analysis of synthetic textile dyes from cultural heritage matrices. Whilst a clean-up system has never before been applied to synthetic dyes within cultural heritage, pre-concentration and pre-treatment protocols are frequently reported for analysis of the same type of dyes used in food colourants. For this reason, this research adapts a DLLME method from the analysis of edible products, and combines this with the state-of-the-art ammonia extraction method reported in literature. DLLME protocols for both natural and synthetic dyes were developed and optimised first on known analytical standards, considered representative of the possible structures of natural dyes and synthetic azoic acid dyes respectively. The extraction recoveries of a variety of disperser and extraction solvents were analysed using HPLC coupled with targeted mass spectrometry. The optimised conditions were then coupled with the ammonia based extraction to ensure coherence of the methods. The results showed significant improvements in the recovery of natural dye analytes compared to current methods, as well as increased precision and efficiency. For synthetic dyes, results showed adequate recovery of analytes and allowed the ammonia-based extraction method to be applied successfully for the first time. After optimisation, the protocol for synthetic dyes was applied successfully to 15 samples (11 fibres, 4 powders) of suspected azo dyes from the Azienda Coloranti Nazionali e Affini (ACNA) synthetic dye collection housed at Sapienza University of Rome’s Museum of Chemistry. The novel protocol was performed after preliminary Raman screening to obtain some introductory information about the unknown samples in the collection. After application of the novel protocol, the samples were identified through untargeted analysis by HPLC-HRMS.