14C Measurements on Santa Catalina petrosal bones
Creators: name: Daniel Garcia Martinez
name: Pedro R. Moya-Maleno
Publisher: name: Zenodo
Year: 2023
Subjects: 14C
Petrosal bone
Radiocarbon Age
Thermo Flash
samples
bones
fossils

description: Sample preparation
CSN'13_CEF6 - Petrosal bone
CSN'13_CEF8 - Petrosal bone
SCT'15_T1UF21_5005 FI4767, FI4775 Petrosal bone
SCT'15_T1UF21_5006 Fi4763, Fi4765 Petrosal bone
Before any radiocarbon measurement, the sample to be dated has to be prepared in order to remove all the possible contaminations and to isolate the original carbon.
As a first step, for each of the samples, the portion chosen for the measurement was first mechanically cleaned using a scalpel to remove the most external layers and then crushed. Since a translucent material, probably indicating the use of some consolidating product, was present on the samples, we decided to clean the selected powdered material by several extractions in chloroform before proceeding with collagen collection. Four extractions in chloroform were applied. Then, collagen was extracted following the so-called Longin method:
• complete demineralization in aqueous 0.5M HCl at room temperature for about 24 hours, at least;
• purification in aqueous 0.1M NaOH at room temperature for 2 hours;
• further bath in 1M HCl at room temperature for 2 hours to remove any CO2 possibly absorbed from atmosphere during the previous step;
• gelatinization of the collagen-based acidified solution (pH ~3) at 80°C.
During this procedure, collagen cannot be extracted from samples CSN'13_CEF6 and CSN'13_CEF8. Actually, after the pre-treatment, the two samples showed significant reddish residues (see Figure 2), which were insoluble in acidic solution (such a behaviour suggests that the original bone matrix might have replaced by other minerals).
After pre-treatment, carbon was extracted from SCT'15_T1UF21_5005 and SCT'15_T1UF21_5006 samples as gaseous CO2 by combustion in elemental analyser (CHN
Thermo Flash1112) and then converted to graphite, i.e. solid carbon, exploiting the reaction of carbon dioxide with hydrogen (with iron as catalyst). Two separate fractions from the same cleaned sample were independently combusted and graphitised (see Table 1 for the laboratory codes).
Results
Graphite pellets were measured by Accelerator Mass Spectrometry (AMS) at the dedicated beam line of the Tandem accelerator at INFN-LABEC laboratory in Florence.
Radiocarbon concentration in the unknown samples was estimated by normalizing the measured 14C/12C isotopic ratios to the 14C/12C ratios measured for a set of samples prepared from a standard reference material (NIST Oxalic Acid II, 134.06 pMCi). Measured isotopic ratios were also corrected for isotopic fractionation, by measuring the 13C/12C ratios, and for background, by measuring blank samples, i.e., samples with nominally no 14C. Table 2 shows the summary of results: 14C concentrations and conventional radiocarbon age are expressed as pMC and years BPii, respectively. For each sample, the weighted average of the concentrations measured in the two prepared graphite pellets was calculated, after verifying that they were statistically consistent.
The calibrated ages were obtained using OxCal v.4.4.2 software, taking into account the calibration curve IntCal20iii as a reference. The age ranges are reported at 68% and 95% of probability, respectively.According to the international agreement, the two samples, whose radiocarbon age is less than 200 years BP, can be classified just as moderniv. 
Nevertheless, for further information, figures 3 and 4 show calibrated ages. IntCal20 calibration curve, with its experimental uncertainty, is drawn in blue; the measured radiocarbon age is reported in red on the y axis and treated as a Gaussian distributed random variable (the experimental error corresponds to the width of the Gaussian distribution); the distribution of probability for the calibrated age is shown on the x axis in dark grey.
Footnote: measurements data reported here were the result of the best of the experience of the laboratory, considering our knowledge of the conservation and selection conditions of the samples
"This report acknowledges the financial support of the Access to Research Infrastructures activity in the H2020-INFRAIA-2019-1 of the EU (IPERION HS Grant Agreement n. 871034)"