Determination of elemental and organic carbon on damaged stone monuments

An analytical methodology was developed for the discrimination and evaluation of the different types of carbon matter, particularly carbonate, elemental and organic carbon, present on monuments and historical buildings, due to interaction between materials and atmospheric pollution. With this aim samples of black patinas were analysed by a procedure consisting of three different steps. Total, noncarbonate and elemental carbon were measured by combustion-chromatographic CO2 determination: Ct was obtained by burning the bulk samples (step 1), while Cnc and Ce were quantified after elimination of Cc with acid treatment (step 2) and elimination of Co by means of alternate attacks, followed by centrifugation, with concentrate acid and base solutions at high temperature and pressure (step 3); the carbonate carbon and the organic carbon were then calculated. Furthermore, for a complete sample characterization, oxalate, acetate, formate and the main anion contents were detected by ion chromatography. The methodology was also tested on standard samples containing the same carbon species as the black crusts. The results obtained indicate that this approach satisfactorily distinguishes between elemental and organic carbon and allows reliable elemental carbon determination at the ppm level in black damage crust samples from historic monuments and buildings.