Liquid chromatography determination of natural dyes in extracts from historical Scottish textiles excavated from peat bogs

Extracting natural dyes from wool—an evaluation of extraction methods

“…The procedure was the same as in HCl-1 method, but after the drying process, 400 μL of MeOH/DMF (1:1, v/v) solution was added to the residue, and the solution was heated at 100°C for 5 min [11]. Vials were cooled to room temperature, and the solvent was evaporated under vacuum.…”

“…Surowiec et al [28] in a study of archaeological Coptic textiles proposed an extraction procedure of alkaline hydrolisis, for samples containing blue dyestuffs (indigotin or its derivatives), based on hot pyridine, while yellow and red dyes were extracted by acidic hydrolysis with a mixture of 3 mol dm −3 HCl solution in ethanol (1:1), heated in a water bath at 90°C for about 30 min. Later, Surowiec et al [11], based on the acidic extraction with a mixture of 37% hydrochloric acid: MeOH:water (2:1:1, v/v/v) in a water bath at 100°C for 10 min, proposed an additional DMF/MeOH (1:1, v/v) extraction step to enhance the extraction of the vat dye indigotin, a component of the blue dyes woad and indigo, and mordant dyes released during hydrolysis step. The recovery efficiencies for flavonoids, plant-derived anthraquinones, ellagic acid and indigotin were improved with this additional MeOH/DMF extraction step and, particularly, the recovery of indigotin offered a notable improvement.…”

“…When indigoids dyestuffs are present in the fibre, the use of DMF [27], hot pyridine [28], MeOH/DMF [11] or dimethylsulfoxide (DMSO) [21] for the residue solubilisation is recommended instead of MeOH or MeOH/H 2 O, since indigotin and indirubin are insoluble in these solvents [11,21].…”

“…Dye analysis is usually performed by liquid chromatography with a diode array detector [6][7][8][9][10][11], but nowadays, mass detection is becoming increasingly important [12][13][14][15][16][17][18][19][20]. A successful approach to identify natural dyes requires that, prior to the chromatographic analysis, an adequate analytical methodology is used for their extraction from the textile fibres.…”

“…The chemical structure and properties of the different dye chromophores suggest that probably no single procedure is adequate for the dye's extraction. Despite the obvious importance of the sample preparation methodology for the ultimate relevance of the analytical data collected, few systematic studies on the recovery rates of the different chromophores with the available extraction methods have been published [11,16,21]. One of the most commonly used extraction methods involves the use of hydrochloric acid (HCl) and methanol (MeOH) at high temperature [5-7, 11, 14, 16, 17].…”