The Heterogeneity Problem: Intermolecular Forces as They Relate to Solubility and Chromatography

Abstract

There is an inherent heterogeneity in works of art and with samples removed from them; this is the heart of many challenges to be addressed by art conservators and scientists. The problem of heterogeneity in art conservation analysis comes from recognizing that we rarely have a completely uniform chemical sample. But, without an understanding of the components (their identity and chemical and physical behavior) of the heterogeneous sample, conservation treatments and art historical interpretations can become more difficult. This is where the knowledge of chemistry principles and theories can assist in making informed choices. This chapter starts with the basics and develops the idea of heterogeneity at the molecular level to its consequences in art conservation practice. The molecular and intermolecular sources of solubility differences are discussed. This eventually leads to an explanation of Teas diagrams, a tool commonly used in art conservation to determine solvents for many uses. Aqueous solubility of ions and surfactants are discussed. Building on the knowledge of intermolecular forces, paper, high performance liquid and gas chromatography are introduced. Identification by mass spectrometry is explained with figures and analogies, and an example is given from a work of art in the National Gallery of Art collection. This chapter is modular and can be used in full or in parts to assist art conservators to more fully understand the chemistry they use every day. It is also useful for both General and Analytical Chemistry courses. Learning Objectives and Assessment exercises are given to assist the instructor and students for all these uses.