ORIGINAL PAPER Analytical diagnosis methodology to evaluate nitrate impact on historical building materials M. Maguregui & A. Sarmiento & I. Martínez-Arkarazo & M. Angulo & K. Castro & G. Arana & N. Etxebarria & J. M. Madariaga Received: 15 October 2007 / Revised: 20 December 2007 / Accepted: 8 January 2008 / Published online: 13 February 2008 # Springer-Verlag 2008 Abstract Nitrate salts have become of greater importance in the decay of materials from historical buildings due to changes in the environment. This work presents an ana- lytical diagnosis methodology to evaluate the impact of nitrate salts in mortars and bricks, combining noninvasive and microdestructive analytical techniques together with chemometric and thermodynamic data analyses. The impact of nitrate salts cannot be well ascertained if other soluble salts are not taken into account. Therefore, the principal results from this work relate to nitrate salts but some results for other kinds of salts are included. Data from Raman microprobe spectroscopy and micro X-ray fluorescence (μ-XRF) are used to characterise the original composition and a first approximation of the nature of the decay com- pounds, mainly nitrates. The soluble salts are extracted and the anions and cations are quantified by means of ion chromatography with conductimetric detection for anions/ cations and inductively coupled plasma mass spectrometry (ICP/MS) for cations. The values obtained allow two dif- ferent data treatments to be applied. First, chemometric analysis is carried out to search for correlations among anions and cations. Second, thermodynamic modelling with the RUNSALT program is performed to search for en- vironmental conditions of soluble salt formation. All the results are finally used to diagnose the impact of nitrates. Keywords Mortar . Brick . Raman microprobre . Micro X-ray fluorescence . Ion chromatography Introduction Cultural heritage, including buildings, forms the basis of our present and future. Historical buildings not only provide a rich diversity of learning but also revenue through tourism. Therefore, extensive efforts have been made to identify the different decay pathologies and decay mechanisms involved in order to look for strategies focused on future restoration and preservation of building heritage [1]. Building materials suffer diverse mechanisms of deterio- ration due to chemical, physical and biological phenomena that are caused by atmospheric factors. One of the principal results of these kinds of deterioration is the formation of soluble salts [2]. This damage takes place as a consequence of dissolution–crystallisation and hydration–dehydration cycles that contribute to the crystallisation of different salts with different numbers of water molecules within porous building materials, contributing to the porous material decay [3]. In contrast to the previous centuries, when the natural factors contributing to decay (temperature, filling of the cracks by dust particles, freezing of water in the small fissure, etc.) prevailed, nowadays, buildings are affected by the destructive influence of many more anthropogenic pollutants such as aerosols and/or particle deposition (dry and wet deposition) [4, 5]. In the dry depositions, the atmospheric pollutant gases can react with both the porous material surface and the aerosol particles [6]. Moreover, the increase of some factors such as concentration of pollutants, turbulence of the air, heterogene- ity of the surface, chemical affinity between the surface and pollutants can favour the deposition process [7]. Regarding the formation of the soluble salts, some areas of buildings are more susceptible to salt accumulation depending on the prevailing wind direction, the distance from pollution sources, regularity of wetting and wet-drying cycles, etc. Anal Bioanal Chem (2008) 391:1361–1370 DOI 10.1007/s00216-008-1844-z M. Maguregui (*) : A. Sarmiento : I. Martínez-Arkarazo : M. Angulo : K. Castro : G. Arana : N. Etxebarria : J. M. Madariaga Department of Analytical Chemistry, University of the Basque Country, P.O. Box 644, 48080 Bilbao, Spain e-mail: maite.maguregui@ehu.es