Positive and negative-mode laser desorption/ionization-mass spectrometry (LDI-MS) for the detection of indigoids in archaeological purple
Article first published online: 12 MAR 2013
Copyright © 2013 John Wiley & Sons, Ltd.
Journal of Mass Spectrometry
Volume 48, Issue 3, pages 384–391, March 2013
How to Cite
Ribechini, E., Pérez-Arantegui, J. and Colombini, M. P. (2013), Positive and negative-mode laser desorption/ionization-mass spectrometry (LDI-MS) for the detection of indigoids in archaeological purple. J. Mass Spectrom., 48: 384–391. doi: 10.1002/jms.3169
- Issue published online: 27 FEB 2013
- Article first published online: 12 MAR 2013
- Manuscript Revised: 9 JAN 2013
- Manuscript Accepted: 9 JAN 2013
- Manuscript Received: 3 DEC 2012
- laser desorption/ionization mass spectrometry;
- cultural heritage
Laser-based ionization techniques have demonstrated to be a valuable analytical tool to study organic pigments by mass spectrometric analyses. Though laser-based ionization techniques have identified several natural and synthetic organic dyes and pigments, they have never been used in the characterization of purple.
In this work, positive and negative-mode laser desorption/ionization mass spectrometry (LDI-MS) was used for the first time to detect indigoids in shellfish purple. The method was used to study organic residues collected from archaeological ceramic fragments that were known to contain purple, as determined by a classical high-performance liquid chromatography-based procedure.
LDI-MS provides a mass spectral fingerprint of shellfish purple, and it was found to be a rapid and successful tool for the identification of purple. In addition, a comparison between positive and negative mode ionization highlighted the complementarity of the two ionization modes. On the one hand, the negative-ion mode LDI-MS showed a better selectivity and sensitivity to brominated molecules, such as 6,6'-dibromoindigo, 6-monobromoindigo, 6,6'-dibromoindirubin, 6- and 6’-monobromoindirubin, thanks to their electronegativity, and produced simpler mass spectra. On the other hand, negative-ion mode LDI-MS was found to have a lower sensitivity to non-brominated compounds, such as indigo and indirubin, whose presence can be established in any case by collecting the complementary positive-ion LDI mass spectrum. Copyright © 2013 John Wiley & Sons, Ltd.