UV/Vis spectra recorded for an indigotetrasulfonate (ITS) deoxygenated aqueous
solution mol dm−3, pH4): broken line. Upon reaction with a zinc amalgam pellet, the
blue ITS solution is reduced to leuco-indigotetrasulfonate
(leuco-ITS), signalled by the
decrease in absorbance at 590 nm and the increase at 390 nm (spectra were
recorded every 30 minutes). The insert
diagram illustrates the excitation spectrum (solid line; nm) and emission spectrum broken line; nm) of a mol dm−3leuco-ITS deoxygenated aqueous solution, at pH4.