Letter: The in Situ Identification of Indigo on Ancient Papers

Abdul-Sada A.K. Barnard M. Lawson P. Brovenko N.M. Petrosyan Y.A. Gibbs P.J. Jordan J.G. and Seddon K.R. , Eur. Mass Spectrom. 1, 217–219 (1995).

Barber M. Bordoli R.S. Elliot G.J. Sedgwick R.D. and Tyler A.N. , Anal. Chem. 54, 645A (1982).

Pachuta S.J. and Cooks R.G. , Chem. Rev. 87, 647–669 (1987).

Gibbs P.J. and Seddon K.R. , British Library Special Publication, in press.

The mass spectometer (a VG Autospec) has a sample holder for L-SIMS, known as a target, with an area of 5 mm × 1 mm. With this particular instrument, a sample size of at least 3 mm × 1 mm is required to ensure a “hit” with the ion beam; if the accuracy of the ion beam were increased, the sample size could be reduced to as small as 1 mm². Similar constraints applied to the FAB probe on a Kratos mass spectrometer.

Oka H. Ikai Y. Ohno T. Kawamura N. Hayakawa J. Harada K-I. and Suzuki M. , J. Chromatog. A 674, 301–307 (1994).

Gower J.L. , Biomed. Mass Spec. 12, 191–196 (1985).

It should be noted that one of the solvent systems appeared to be successful, the 1: 1 mix of DMSO and glycerol. But the strong peak at m/z 263 (as expected for protonated indigo) is attributable to the matrix [2 glycerol (RMM = 92) + 1 DMSO (RMM = 78) + 1 proton = 263]. In confirmation, the DMSO was replaced with DMSO-d₆ (RMM = 84), and no peak at 263 was observed.