Characterization of Different Chemical Procedures for¹⁴C Dating of Buried, Cremated, and Modern Bone Samples at Circe

Abstract

ABSTRACT. Bone chemical treatment for radiocarbon dating has drawn the attention of different laboratories because dates of bones and charcoals found in the same layer often disagree. Excluding diet-related reservoir effects, this observation is likely due to a nonoptimized procedure of contaminant removal from the extracted collagen. In this study, systematic work on the bone chemical treatment was performed with the aim to investigate the effect of each known procedure (i.e. AAA, GEL, and ULTR) on the collagen used for 14 C dating. Isolation and purification of lipids from animal tissues were performed to estimate eventual offsets induced by the applied methods, by comparing the 14 C ages of lipids with those of collagen. Moreover, cremated bones were treated for the first time at CIRCE. Measured 14 C isotopic ratios on these samples were used to evaluate the accuracy of the applied procedure by comparing against the results for charcoals found in the same archaeological context as the bones.

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“…The sample preparation methodology at PSU was carried out as previously reported 58 , where bone collagen was extracted and purified using a modified Longin method with ultrafiltration 59 (>30 kDa gelatin); if collagen yields were low, a modified XAD process 60 (XAD amino acids) was used. Sample preparation at CIRCE was carried out following the lab-adapted Longin method 61 . Supplementary Data 3 lists the preparation method used for each sample.…”

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“…Then the GEL fraction was obtained by heating the collagen to 70°C in a solution with pH 3 for 20 h [23]. Finally the gel was freeze-dried and used for the successive combustion and graphitization processes [24,25].…”

“…Several rinses with de-ionized water were carried out after each step, until neutrality was achieved, before drying the samples in an oven. Finally the gelatinization protocol [23] was applied. In order to test the quality of the collagen, C and N fractions of dry collagen were measured by an elemental analyser (CN Flash EA 1112, Thermo Scientific, Bremen) and expressed in % C and % N. Samples were retained for isotope analyses provided the extracted collagen achieved a yield higher than 1% and an atomic C:N ratio between 2.9 and 3.6 [33][34][35] …”

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“…Samples of about 1 g from each US were pulverized and chemically treated for the collagen extraction, performed by following standard procedures used at CIRCE and described by Passariello et al [12].…”

“…One portion of the collagen was treated to a GEL stage, and the second collagen portion underwent to gelatinization and then ultrafiltration (ULTR) to evaluate the possible differences introduced by different sample preparation methods (Table 1). Ultrafiltration was performed by means of Vivaspin™ 15-30,000 MWCO filters, after their cleaning with ultrapure water [12].…”