DMSO and DMF are selected for the detailed comparative investigation,
because theywere previously used to treat vat and direct dyes and
were furthermore recommended for the treatment of unknown historical/
archaeological samples prior to acid hydrolysis [2,20–25]. In our
initial preliminary experiments, the extraction efficiencies of pyridine
and ethyl acetate were also evaluated. However, these two solvents
were eliminated fromthe subsequent detailed study, as the preliminary
results showed that both DMSO and DMF provide clearly better extraction
yields. This finding is in agreementwith previously published, brief
investigations