M. Járó - L. Költő szerk.: Archaeometrical research in Hungary (Budapest, 1988)

Dating - CSAPÓ János, KÖLTŐ László , PAP Ildikó: Archaeological age determination based on the racemization and epimerization of amino acids

cleaned, washed and the contamination is generally removed by ultrasonic methods (Bada and Protsch, 1973; Wehmiller and Hare 1971). The sample is then dried and milled, after which the homogeneous mixture is ready for the extraction of amino acids. The sample is washed in dilute hydrochloric acid in order to free the amino acids. The mixture containing the free amino acid is removed by filtration from the remaining mixture containing the unextractable amino acids (Dungworth et al, 1975). The free amino acids are then ready for determining the D- and L-amino acids. (In some cases, a desalting may be justifiable.) The non-decomposable remainder is then hydrolyzed for 22-24 hours at 100-110 °C with hydrochloric acid of 6 moles, as in the usual process of amino acid analysis. Following the completion, the hydrochloric acid is removed by distillation, the residue is diluted in distilled water and is desalted. For desalting some experts prefer the removal of calcium (Wehmiller and Hare, 1971), while others apply the feeding of the compound through cation or anion-exchanging resin (Kvenvolden et al, 1970). It is not feasible to apply alkaline treatment during the preparation of the sample nor during the extraction of amino acids, as these are liable to racemization, and this should certainly be avoided during the prépara

tional phases. Several methods have been elaborated for the separation and determination of amino acid enantiomers. Initially polarimetry was used, which was mainly applicable to the examination of the racemization of clean amino acids (Bada, 1971; 1972, Sato et al, 1970). An enzyme technology was used to determine the D- and L-amino acids in soil (Aldag et al, 1971) and from some fossils (Hare and Abelson, 1967; Hare, 1969 and Petit, 1974). This method consists of the oxidation of the D- and L-amino acids, followed by the determination. The problem with the method is that it is not applicable for determining the traces of D-amino acids, and therefore it can be the source of error in the case of L-amino acids originating from enzymes. Manning and Moore (1968) have described an ion-exchanging column-chromatographic method for the separation of D- and Lamino acids. This is based on the reaction of an L-amino acid N carboxi anhydride on the D- and L-amino acids to be determined. Diastereomer dipeptides are formed that can be used for the ion-exchange separation. With this method Bada and Protsch (1973) succeeded in analysing aspartic acid from bone in the form of L-Leu-D-Asp and L-LeuL-Asp diastereomer dipeptide. One of the best methods for separating D- and L-amino acids - apart from high pressure liquid chromatography - is gas-chromatography. The enantiomers can be separated in the form of a diastereomer-pair prepared by an asymmetric reagent or, alternatively, on the basis of the derivatives separation by an optically active phase is possible

. Charles et al. (1963)used N-trifluoracetil-(±) 2-n-alcohols to prepare diastereomers. This method has been improved with the application of (±) 2-n-butanol by Pollack and his team in 1965; and Kvenvolden with his team made this suitable for the needs of organic geochemistry in 1971. The first optically active stationary phase in gas-chromatography was the N-trifluor-acetyl-D-isoleucine-lauril-ester, which was synthesized by Gil-Av et al. in 1966. Charles (Î975) used the N-lauril-L-vahl-tertier-butylamide to separate optical isomers. The technique of gas-cliromatography has been improved to such a degree that the error in determining the enantiomers is less than 5%, and reproducibility is extremely good. Nowadays high pressure liquid chromatography is used to an increasing degree for the separation of enantiomers. Weinstein and Weiner (1984) have prepared a fluorescent derivative, the 5-dimethyl-aminonaphtahne-l-sulpholin from the amino acids, and with an inverse phase liquid chromatography the N, N'-di-n-propyl-L-alanine (L-DPA) and