Use of amino acids and their racemisation for age determination in archaeometry

Abstract

After reviewing previous attempts to use the extent of amino acid racemisation (AAR) for the determination of the age of archaeological samples containing proteins, the authors describe their own approach. Following an optimised protein hydrolysis with low racemisation the d- and l-amino acid content in fossil bone samples of known age (radiocarbon method) was determined by HPLC after precolumn derivatisation. Based on the obtained half-lives of racemisation and plotting the d/ l ratio as a function of time for various amino acids, calibration curves are obtained which can be used for the age determination of fossil bone samples in the range of 2000–500 000 years. Another method is presented for the determination of age of textiles in the range of 100–1800 years. This method is based on the determination by an amino acid analyser of the age-dependent alteration of amino acid composition of proteins. Cystine, methionine and tyrosine content decreases, while cysteic acid content increases with age. Prediction equations were developed as linear regressions of the age of wool based on cysteic acid, cystine and tyrosine contents.