Achaeometrical Research in Hungary II., 1988

PROSPECTING and DATING - János CSAPÓ - Zsuzsanna CSAPÓ-KISS - János CSAPÓ JR.: How the amino acids and amino acid racemization can be used and with what limits for age determination of fossil materials in archaeometry

materials for AAR testing, particularly if they come from a warm environment. The statement was based on differences observed between the age of the California bones determined by C

14 accelerator mass spectrometry (5,000 - 6,000 years) and by AAR (50,000 - 60,000 years). MILFORD WOLPOFF, a palaeoanthropologist, expressed the opinion (cited by MARSHALL, 1990), that many people currently regard AAR as „some kind of joke". Since various changes in temperature during the past and other conditions influencing dead biological organisms are not well known, the reaction temperature of racemization can only be estimated and not accurately determined. This is the reason why - in this study - contents of D- and L- amino acids and their ratio were determined in samples of known ages (as determined by the radiocarbon method). These data were then compared with data obtained from the analysis of amino acids in samples of unknown age. To make the comparison more accurate, the antecedents of samples of known age when analysed were the same as or similar to those of unknown ages. Therefore, approximately 100 fossil bone samples, previously analysed by the radiocarbon method, were collected from various Hungarian museums, and their D- and L- amino acid contents were determined. The D/L ratio was calculated and plotted against time which produced a calibration curve. This curve can be used in the age estimation of samples of unknown age after their D- and L- amino acid contents have been determined. The D/L ratio for 2 to 3 various amino acids was determined for each sample and the mean value of ages estimated from calibration curves was considered the true age of the fossil sample. 2.2. Materials and methods 2.2.1. Sample preparation The samples were washed in running- and distilled water, dried in a vacuum drying oven and ground to produce a powdered material as fine as flour. Apolar contaminants were removed with petroleum ether in a Soxhiet extractor for 3 hours at 40 °C. The free amino acids were extracted by 0.Î M HCl solution for 16 hours. The nitrogen content of the residue was determined by Kjel-Foss nitrogen analyser. Sample size (200-2 000 mg residual material containing app. 10-20 mg protein) was dependent on nitrogen content. Samples were weighed and hydrolysed with 6 M HCl at 110 °C for 24 h. HCl was removed by lyophylysation, the residue was dissolved in water, and the precipitated silicate compounds were separated from the liquid containing free amino acids using a centrifuge. The solution was alkalised to pH=9 for a moment and precipitated metal hydroxides were filtered. The hydrolysed solution was neutralised and evaporated to dryness by lyophylysation. 2.2.2. Determination of amino acids An aliquot of hydrolysed material was dissolved in a citrate buffer solution of pH=2.2 and isoleucine and D-allo isoleucine were determined by LKB 4101 type amino acid analyser as described by CSAPÓ ET AL. (1986). The other D- and L- amino acids were separated in the form of alanyi- (CSAPÓ ET AL., 1991a) and 2-suîphonylic acid alanyi diastereomerisomer dipeptides (CSAPÓ ET AL., 1990b) by ion exchange column chromatography and by the method of EINARSSON ET AL. (1987b) with reversed-phase HPLC using precolumn derivatization with the chiral reagent O-phthalaldehyde/2,3,4,6,tetra-O-acetyl1 -thio-ß-glucopyranoside. .?/