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
A mean of estimates based on two amino acids would have a standard error of S.E.= Jl\Sy + sj 1/4 and 95% confidence limits can be established as С I. = Mean of two Y values ± S.E. (t 0 .os). Since the average based on the smallest number of samples would have 15 degrees of freedom, the value of t 0 .os used in the following estimates was 2.13. The ± deviations were calculated for each pair of amino acids and are shown below. The confidence intervals at mean values are shown above the diagonal and confidence intervals at extreme values are below the diagonal: Phe Asp Ala He Phe 313 454 388 Asp 601 473 409 Ala 1109 1160 524 He 650 733 1186 If both D/L values were near the mean, we would be 95% confident that our estimate was in the range of mean Y ± 313 to 524 years. If both estimates were based on extreme values of D/L, we would be 95% confident that our estimate was in the range of mean Y ± 601 to 1186 years. The confidence interval for each estimate of age of an unknown sample would be calculated individually. Finally, the applicability of calibration curves is presented. As an example, one bone sample of unknown age was analysed for L- and D-amino acids and the following results were obtained: L-His: 0.0697 mg, D-His: 0.0289 mg, D/LHis= 0.428. Age calculated from calibration curve: 7100 year; S.E. = 337. L-Phe: 0.0543 mg, D-Phe: 0.0138 mg, D/LPhe=0.254. Age calculated from calibration curve: 6950 year; S.E. = 191. L-Asp: 0.1346mg, D-Asp: 0.0245 mg, D/LAsp=0.182. Age calculated from calibration curve: 6900 year; S.E. = 465. The estimated age of the sample is the mean value of the above estimates or 6980 years. This mean value has a standard error of 202 years and the 95% confidence interval would be 6554 to 7406 years. 2.4. Conclusions The D- and L-amino acid composition was determined in fossil bone samples of known age. Ages were determined by the radiocarbon method. The D/L ratio was plotted as a function of time which resulted in a calibration curve which can be used for age estimation after the D- and L-amino acid contents in samples of unknown age have been determined. However, this method includes the analytical error of age estimation by the С method, but the effects of temperature, pH and the composition of soil on AAR can be eliminated. The D/L ratio for 2 to 4 amino acids should be determined for each sample, and the mean value of estimated ages based on calibration curves is considered the best estimate of age of the fossil sample. 35
