Chromatographic analysis of indigo from Maya Blue by LC–DAD–QTOF

Indigotin and indirubin, main components of indigo dye, extracted from Maya Blue pigment, have been separated and identified by liquid chromatography coupled to a diode array detector and a mass spectrometer with a quadruple-time-of-flight analyser (LC–DAD–QTOF). The development of a suitable extraction method combined with the powerful capabilities of the LC–DAD–QTOF system (combination of mass accuracy, high sensitivity and mass/mass (MS/MS) data), allowed the identification of indigotin and indirubin in blue and green microsamples of less than 0.1 mg, taken from the some drawings contained in one of the Códices Matritenses by Fray Bernardino de Sahagún (16th century). This provides a valuable tool for systematic investigation of Maya Blue from archaeological materials, especially from manuscripts, where the available sample amount is generally veriest restricted.

► A novel and rapid extraction method for indigo from Maya Blue was developed.
► Indigotin and indirubin were identified by LC–DAD–QTOF.
►  For the first time indigo components in Maya Blue could be chemically confirmed.
► Maya Blue was identified in three samples from a 16th century codex by B. Sahagún.
► The study provides a helpful tool to determine Maya Blue in archaeological material.