Estimation of Chronological Age from the Racemization Rate of l- and d-Aspartic Acid: How to Completely Separate Enantiomers from Dentin

Estimation of chronological age is essential in forensic and archeological science. The racemization method is one of the best methods to meet the demands of these scientific fields, providing both accuracy of the estimated age and simplicity of technique. In general, living organs are composed of
l-form amino acids. Conversion from
l-form to
d-form amino acids is a first-order chemical reaction. Thus, the quantity of
d-form amino acids in an organ is proportional to the passed time (age) after organ completion if no protein turnover occurs after organization. However, every living organ undergoes some degree of protein turnover. Therefore, organs with low metabolic rates, such as teeth and bone, should be targeted for the racemization method. The most critical point of the technique may be the complete separation of
d- and
l-forms by gas chromatography because of the very small amounts of
d-form amino acids present. We describe the detailed procedures and the critical points for obtaining reliable estimated ages using the racemization method.