Amino Acid Racemization Dating

Amino acid racemization dating (AAR) is a valuable technique used in geochronology and archaeology for estimating the age of biological materials based on the extent of racemization of amino acids. L-amino acids and D-amino acids are the two mirror-image forms, or enantiomers, of amino acids, which are the building blocks of proteins. Racemization is the process by which the L-amino acids gradually turn into D-amino acids, changing the ratio of these enantiomers over time. Amino acid racemization dating requires a number of important processes. Initially, a sample comprising of organic components is taken from the relevant geological or archaeological site. A rock from the Bahamas served as the sample. After that, acid hydrolysis is used to extract the amino acids from the sample. A two-step derivatization procedure including capping the side chains of the amino acids extracted from the sample may be used prior to the amino acids being submitted to gas chromatography. By changing amino acids into more volatile and stable derivatives, this procedure seeks to improve amino acid separation and detection. Using thionyl chloride and 2-propanol, one amino acid side chain is capped in the first step. Then comes the second derivatization, which caps the opposite side chain and uses pyridine and trimethyl acetyl chloride. As a result, the D/L enantiomers are more suited for gas chromatographic examination since they can separate more effectively. The derivatized amino acids were dissolved in methylene chloride and injected into the GC column using an autosampler to determine the relative abundance of L- and D-amino acids.