The Analysis of Indigoid Dyes by Mass Spectrometry

High-resolution mass spectrometry provides an expeditious technique for positively identified indigoid dyes of molluscan origin. Indigoids on modern and ancient textile fibres, as well as indigoid mixtures produced by reactions, are discussed. Steam treatment of the fibre or isolation of the dye by solvent extraction permits the analysis by mass spectrometry of dyes which bind more tightly to fibres, such as 6,6′-dibromoindigotin (C.I. 75800, Natural Vat Dye). The demonstration of the stepwise photolytic debromination of the leuco base of 6,6′-dibromoindigotin may be of more far-reaching significance in distinguishing between natural and intentional mixtures of indigotin and its dibromo derivative