Identification of plant and animal glues in museum objects by GC-MS, aftercatalytic hydrolysis of the proteins by the use of a cation exchanger, with simultaneous separation from the carbohydrates

A method is described which enables the group-separation of proteinaceous b inding media from vegetable glues (carbohydrates), and simultaneous hydroly sis of the proteins in mixtures of both. The mixtures of the binders are su spended in aqueous-ethanolic solvent with the H+ form of a strong cation ex changer and treated at elevated temperature in scaled vials. The polypeptid es are cleaved by H+-catalysed hydrolysis. On abstraction the amino acids a re transformed into the ammonium ions by the protons, and the cations are a dsorbed by the exchanger resin. The amino acids are retrieved from solution in this way, thus suppressing interfering reactions with other binders, e. g. humin formation with carbohydrates. Clear and colourless solutions were obtained with all mixtures of vegetable and animal glues. Two fractions can be obtained after separation of the solid resin from the liquid supernatan t - the resin fraction with the adsorbed amino acids, and the aqueous-ethan olic solution with the carbohydrates. In each of these fractions the two cl asses of binder can be identified separately by GC-MS; this avoids the occu rrence of unresolved GC peaks and superimposed mass spectra. The method has been used to identify the binder found between fabric layers of a Burgundian liturgical vestment of the Order of the Golden Fleece from the first half of the 15th century, the Cope of the Virgin Mary. With the aid of the GC pattern obtained, and the mass spectra of the main peaks, whi ch were identified as glucopyranose anomers, the binding medium was identif ied as starch.