Chemical techniques to extract organic fractions from fossil bones for accurate 14C dating

We examined different concentrations of HCI, such as 0.4, 0.6, 0.8, 1.0 and 1.2 M, for decalcification of fossil bones and different times of 0.1 M NaOH treatment on collagens to determine the best conditions for purifying collagen through extraction of humic contaminants, and compared the alkali treatment method with the XAD-2 treatment method for several types of fossils. The yield of acid-insoluble bone fractions did not change over the range from 0.4 to 1.0 M HCI and decreased suddenly with 1.2 M HCl on decalcification, and the 14 C ages of the extracted gelatins from the five decalcified fractions were unchanged, suggesting that <1.0 M, and probably about 0.4 M, is recommended to the best concentration of HCI to decalcify fossil bones efficiently. The alkali treatment was done with 0.1 M NaOH at room temperature. The NaOH-treated collagens, with a considerable loss of organic bone protein especially for long treatment time, gave almost the same C-14 ages as those of the XAD-purified hydrolysates. The NaOH-treatment time should be less than several hours to avoid a loss of collagen. The fossil bones used are relatively well-preserved, but the alkali treatment could bring about a lot of loss of organic bone proteins for poorly-preserved bones. The XAD-2 treatment method is effective for accurate radiocarbon dating of fossil bones, if the XAD-2 resin is completely precleaned. (C) 2004 Elsevier B.V. All rights reserved.