UV-induced degradation of wool and silk dyed with shellfish purple

The effects of harsh UV radiation (lambda = 254 nm) on wool and silk dyed with Hexaplex (Murex) trunculus extract are investigated using HPLC-DAD, colourimetry, SEM and FTIR. Indigotin, 6-bromoindigotin, 6,6'-dibromoindigotin and 6,6'-dibromoindirubin were quantified by an efficient HPLC-DAD method which was validated in terms of linearity, detection and quantification limits, precision and accuracy. Under optimal conditions, the developed analytical scheme offers limits of detection in the range 0.02-0.12 mu g mL(-1) and satisfactory linearity up to 5.0 mu g mL(-1). The purple dyes, extracted from the wool and silk fibres, were analysed by the established HPLC method, using the standards addition approach. To evaluate the matrix effect, the matrix-induced signal suppression/enhancement was determined. The accuracy was evaluated by recovery experiments. The effect of the UV light was initially dramatic, leading to (i) a rapid decrease in the amounts of the four shellfish compounds in the wool/silk fibres and (ii) severe colour changes of the dyed fibres. After extensive ( > 10 days) exposure in harsh UV light, only slight changes in the dye composition and the colour of the fibres were observed. Overall, larger reductions are reported in the amounts of the dibrominated molecules, whereas indigotin and 6-bromoindigotin appear to be more stable against the UV radiation. However, it is reported that the % relative composition of the shellfish dye is practically unaffected by the degradation process. Finally, the UV-induced structural and chemical changes of the wool and silk fibres were investigated using SEM and FTIR, respectively.