Complementary protocol of investigation of proteinaceous additives in historical mortars

Proteomics is a novel area with many potential applications to the field of cultural heritage conservation and heritage science, mainly as far as the analysis of proteinaceous components (binders, adhesives, plasticizers and other additives) is concerned. Mortars from monumental structures were prepared according to various recipes employed since ancient times using natural additives such as milk (curd, whey, cheese and casein), blood and egg proteins. Mass spectrometric and immunological assays are valid techniques to be applied in the identification and quantification of the proteinaceous components of historical mortars. This paper presents preliminary results of research undertaken on model (fresh and aged) and real samples of mortars (from historical monuments in the Czech Republic) using a complementary approach based on MALDI-TOF-MS (Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry) and ELISA (Enzyme-Linked Immunosorbent Assay). Both techniques are micro-destructive, requiring small quantities of samples (range from 0.5-10 mg for fresh model samples, see Experimental part; 50-200 mg for real samples) but their high sensitivity and selectivity make them a valid alternative to other, more conventional techniques (micro-FTIR, GC-MS etc.). The peptide mass mapping method was successfully used for identification of protein additives in real samples, while the ELISA assay confirmed the presence of a proteinaceous component (bovine casein and/or egg) as well as the measurement of the amount of casein (and possibly egg) present in the analysed samples. The influence of ageing of the mortar on identification of protein additives and issues related to detection limits and sample preparation are discussed.