Bone preparation at the KCCAMS laboratory
Introduction
Radiocarbon dating of bone is particularly difficult because the porous and easily alterable apatite matrix of bone allows potential contamination of bone collagen by environmentally mobile soil carbon. Brown et al. [1] developed a modified Longin method using ultrafiltration to select large protein fragments (hereafter referred to operationally as “collagen”) most likely to be uncontaminated. This technique has been used in North America for over 20 years (all bone samples prepared by the RIDDL group [1], and subsequently at the CAMS/LLNL and UC Irvine AMS labs, have been prepared with this technique) and is now also being used extensively by researchers at Oxford [2]. Here we describe the technique as used at the UCI-KCCAMS lab and report on tests to maximize collagen yields and to characterize process blanks.
Section snippets
Methodology
Collagen production at the UCI-KCCAMS lab follows a modified Longin method [1]. Approximately 100 mg of bone is manually cleaned and crushed to particles roughly 2 mm in size. The sample is then decalcified in 0.5 N HCl for 24–36 h. After rinsing with Milli-Q water to neutral pH, the sample is hydrolyzed with 0.01 N HCl at 60 °C for 8–12 h. The high MW fraction of the gelatin solution is selected using precleaned 30 kDa Centriprep ultrafilters (Fisher Scientific). The sample is ultrafiltered twice,
Decalcification
Acid strength and decalcification time should be optimized in order to maximize collagen yield. Collagen yield decreases strongly with increasing acid strength and HCl strengths above 1 N should not be used (Fig. 1). Decalcification time is highly dependant on bone preservation state and the size of bone pieces chosen (Fig. 2). We use a 24–36 h decalcification period, with visual inspection to check for completion. Decalcification temperature appears to have little effect on the yield (Fig. 2).
Gelatinization
Conclusions
These and similar samples tests can help to validate bone preparation procedures and can point the way to further improvements such as the rapid gelatinization developed by Semal and Orban [4]. A significant obstacle in such tests has been the lack of a well characterized “dirty bone” standard that is known to be seriously contaminated. We urge all laboratories undertaking bone preparation to be aware of the need for suitably large samples of such material and to report them to the community if
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Address: Cotsen Institute of Archaeology, University of California, Los Angeles, CA 90021, USA.