Assessing Methodological Contamination in Organic Residue Analysis using FT-IR Spectroscopy

Abstract

Organic residue analysis (ORA) has become a mainstay in modern archaeological and conservation research. Organic residues recovered from archaeological and conservation contexts represent an accumulation of materials by original deposition and post-depositional processes. However, the organic material of interest in the residue can be obscured by contaminants from the environment, and field and laboratory materials. Fourier Transform Infrared Spectroscopy (FTIR) is an analytical technique that is becoming increasingly popular in ORA, due to its ease of use, cheap cost, easily repeatable results, and ubiquity in academic laboratories. Infrared spectroscopy has inherent limitations in differentiating components of mixtures. This brings into questions its effectiveness at differentiating target archaeological analytes from contaminants. In this thesis, the question is asked whether materials commonly used in organic residue analysis projects are introducing analytically significant contaminants which have the potential to obscure data generation, analysis, and interpretation. A research project in ORA using FTIR spectroscopy is presented as a case study to address the research question. My research demonstrates that many field and laboratory materials commonly used in ORA sample recovery and laboratory analysis introduce analytically significant contaminants into samples. These include materials for both general use and those which have been manufactured and marketed specifically for use in spectroscopy. ORA projects using IR spectroscopy are cautioned to acknowledge all potential sources of methodological contamination, engage in rigorous control methodologies to independently assess methodological contaminants in their research, and include primary control data in final project publications.