Preparation of bone carbonate for stable isotope analysis: the effects of treatment time and acid concentration Sandra J. Garvie-Lok a *, Tamara L. Varney b , M. Anne Katzenberg c a Department of Anthropology, University of Alberta, 13–15 HM Tory Building, Edmonton, Alberta T6G 2H4, Canada b Department of Anthropology, University of Manitoba, Winnipeg, Manitoba R3T 5V5, Canada c Department of Archaeology, University of Calgary, Calgary, Alberta T2N 1N4, Canada Received 27 October 2002; received in revised form 22 August 2003; accepted 27 October 2003 Abstract While apatite carbonate  13 C analysis is a useful tool in palaeodietary research, the vulnerability of carbonates to diagenesis necessitates careful sample preparation. The most common preparation method involves dilute acetic acid treatments to remove highly soluble mineral contaminants. However, there is variation in both treatment time and acid concentration. This study addresses the impact of such variation on carbonate  13 C and  18 O, sample loss in solution, and sample Fourier transform infrared spectroscopy (FTIR) characteristics. Samples of fresh and archaeological bone were treated with 1.0 M and 0.1 M acetic acid. Carbonate  13 C and  18 O, sample loss and FTIR characteristics were measured at treatment times of 4 to 24 h. The results suggest that 4 h of treatment suffice to remove highly soluble contaminants, and that longer treatment times can lead to sample recrystallization. Some samples treated with 1.0 M acid showed unacceptable loss or possible recrystallization, suggesting that 0.1 M acid treatment is preferable. However, the more dilute acid caused smaller shifts in  13 C and  18 O for all samples and treatment times. Thus, while 0.1 M acid appears to produce superior sample quality, it may not produce results directly comparable to those of 1.0 M acid treatments. This has important implications for the comparison of apatite carbonate stable isotope values reported in the literature.  2003 Elsevier Ltd. All rights reserved. Keywords: Archaeological bone; Bone carbonate; Bioapatite; Stable carbon isotopes; Stable oxygen isotopes; Sample preparation 1. Introduction The analysis of stable isotopes of carbon in preserved bone collagen for the purpose of reconstructing past diet and ecology has become routine in bioarchaeological studies since its introduction in the 1970s [40,41]. More recently the carbonate in bone mineral has been used as a source of biologically deposited carbon for stable isotope studies. Bone carbonate is present in samples that are very ancient [16] and in samples from tropical regions where preservation is often very poor [12]. When collagen is preserved, analysis of stable carbon isotopes from both collagen and carbonate is useful because the two tissues reflect different dietary sources. Specifically, collagen is formed largely from ingested protein while carbonate is deposited from dissolved bicarbonate in the circulation, which is drawn from all dietary components [1,14,38]. While the use of apatite carbonate  13 C analysis in palaeodietary reconstruction is becoming increasingly common, the vulnerability of bone mineral to diagenesis necessitates careful preparation and evaluation of car- bonate samples to ensure that the biogenic isotopic signals are being obtained. This paper presents the results of a test of varying preparation methods for the isolation of bone carbonate and discusses the chemical properties of samples prepared using these methods. 1.1. Background Sullivan and Krueger [36] first provided evidence that carbon isotopes from carbonate provide useful * Corresponding author. Tel.: +1-708-492-0137; fax: +1-708-492-5273. E-mail address: sandra.garvie-lok@ualberta.ca (S.J. Garvie-Lok). Journal of Archaeological Science 31 (2004) 763–776 SCIENCE Journal of Archaeological http://www.elsevier.com/locate/jas SCIENCE Journal of Archaeological http://www.elsevier.com/locate/jas 0305-4403/04/$ - see front matter  2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.jas.2003.10.014