Two procedures for suppressing interference from inorganic pigments in the analysis by gas chromatography-mass spectrometry of proteinaceous binders in paintings

Two methods for suppressing the interference of inorganic pigments in the determination of amino acids in hydrolysates of wall painting samples by gas chromatography-mass spectrometry are described. One is based on the extraction of proteinaceous matter from the sample by a 2.5 M ammonia solution prior to the hydrolysis step, and the other on the elimination of inorganic ions from the hydrolysate by means of a cation-exchange resin. The proteinaceous binders present in the paint layer were identified using principal component analysis on the relative amino acid percentage. Some samples from "Giudizio Universale" in Florence Cathedral and from the Monumental Cemetery in Pisa (Italy), were analysed using both procedures. The presence of milk binder as the main organic component of the tempers was highlighted. (C) 1999 Elsevier Science B.V. All rights reserved.