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An analytical procedure for the characterization of proteinaceous binders (milk or casein, egg and animal glue) in artistic wall painting samples is described The method is based on microwave-assisted acid hydrolysis of the sample, and on derivatization of the amino acids freed with a silylating agent and their quantitative determination by gas chromatography/mass spectrometry. The procedure was tested on wall painting reference samples, and showed a typical protein recovery of about 70% at 0.1mg sample size. Fourteen amino acids were determined and some ratios between their concentrations were selected, so that the proteinaceous binders in the sample could be identified. Results on some samples from frescoes from the Monumental Cemetery in Pisa (Italy) showed that the amino acid composition of casein differed significantly from that expected, as a result of degradation processes due to aging and moisture. [ABSTRACT FROM AUTHOR]