The requirements of extracting minute amounts of organic carbon in solution with high yield and minimum background are a prerequisite for radiocarbon dating of microgram amounts of carbon. Samples for biomedical or environmental research often arrive at the accelerator mass spectrometry (AMS) lab as concentrates dissolved in 1 mL of water or less. We have developed a new extraction method based on photo-oxidation by ultraviolet (UV) light. The solution is transferred into UV-transparent quartz vials with a head volume of pure oxygen and UV from low-pressure mercury discharge lamps is applied. To exclude the introduction of carbon background, we avoid any additional oxidizing agents. Under these conditions, only the 185 nm line is considered effective. To characterize the yield and the background, we have investigated artificial samples prepared from different materials. The setup developed allows parallel oxidation of 9 samples within typically 2 hr, connected directly to our graphitization setup for extremely small samples. The method was applied successfully for a study on dissolved organic carbon (DOC) in ice from 26 Austrian glaciers. A special advantage of the UV oxidation method in this case was that phosphoric acid could be used to remove carbonates, while its low vapor pressure prevented complete lyophilization. We see the most promising field of application in biomed research and compound-specific analysis.

Carbonaceous particles that comprise organic carbon (OC) and elemental carbon (EC) are of increasing interest in climate research because of their influence on the radiation balance of the Earth. The radiocarbon determination of particulate OC and EC extracted from ice cores provides a powerful tool to reconstruct the long-term natural and anthropogenic emissions of carbonaceous particles. However, this 14C-based source apportionment method has not been applied for the firn section, which is the uppermost part of Alpine glaciers with a typical thickness of up to 50 m. In contrast to glacier ice, firn samples are more easily contaminated through drilling and handling operations. In this study, an alternative decontamination method for firn samples consisting of chiselling off the outer parts instead of rinsing them was developed and verified. The obtained procedural blank of 2.8 ± 0.8 μg C for OC is a factor of 2 higher compared to the rinsing method used for ice, but still relatively low compared to the typical OC concentration in firn samples from Alpine glaciers. The EC blank of 0.3 ± 0.1 μg C is similar for both methods. For separation of OC and EC for subsequent 14C analysis, a thermal-optical method instead of the purely thermal method was applied for the first time to firn and ice samples, resulting in a reduced uncertainty of both the mass and 14C determination. OC and EC concentrations as well as their corresponding fraction of modern for firn and ice samples from Fiescherhorn and Jungfraujoch agree well with published results, validating the new method.

We conducted an interlaboratory comparison between our radiocarbon-related research group at Lund University and the established ETH-Zurich facility to test the quality of the results obtained in Lund and to identify sources of potential background differences and scatter. We did find differences between the 2 laboratories in the contributions of chemical preparation, graphitization, and measurements to the overall background. The resulting overall background is, however, almost similar. Multiple measurements on 2 wood samples of known calendar age yield consistent and accurate 14C ages in both laboratories. However, one of our known samples indicates that IntCal09 is ≃38 ± 16 14C BP too young at 7020 calendar yr BP, which is consistent with one of the raw data sets contributing to IntCal09. Overall, our results show that a systematic approach to compare the different steps involved in 14C age determination is a useful exercise to pinpoint targets for improvement of lab routines and assess interlaboratory differences. These effects do not necessarily become apparent when comparing 14C measurements that integrate over the whole process of preparation and measurement of different laboratories.

Preservation of seawater samples was tested for total inorganic carbon (∑CO2), stable carbon isotope (δ13C), and radiocarbon (14C) applications using foil bags and storage by refrigeration and freezing. The aim was to preserve representative samples with minimal storage effects but without using toxic methods such as mercuric chloride poisoning. Hydrolysis of samples to CO2 was based on existing methods. Results of IAEA-C2 standard used with deionized water stored in the foil bags showed complete reaction yields, 14C results within 2σ of the consensus value, and δ13C that were internally consistent, indicating that there were no procedural effects associated with the foil bags. 14C results were statistically indistinguishable across the storage times, for frozen and refrigerated seawater samples from a coastal site, Elie Ness, Fife, UK. The scatter of ∑CO2 concentrations and δ13C was within scatter observed in other studies for lake- and seawater samples preserved by acidification or using mercuric chloride. However, both ∑CO2 and δ13C were less variable for frozen samples compared with refrigerated samples. The foil bags are lighter, safer to transport, and similar in cost to glass bottles and allow sample collection in the field and transfer to the hydrolysis vessel without exposure of the sample to atmosphere. Storage of seawater samples in the foil bags was considered a reliable, alternative method to poisoning for ∑CO2, δ13C, and 14C, and freezing the samples is recommended for storage time beyond a week.

Cartridges containing a zeolite molecular sieve are used for the field collection of CO2 from a variety of environments (e.g. atmosphere, soil respiration, evasion from surface waters) for accelerator mass spectrometry (AMS) radiocarbon analysis by the NERC Radiocarbon Facility. Previously, sample CO2 was recovered from the sieves by heating under vacuum prior to cryogenic purification and graphitization. An additional heating and evacuation stage was used to prepare the cartridge for the next sample. We have recently developed an alternative method using heating and purging with nitrogen gas to remove sample CO2 from the molecular sieve. An infrared gas analyzer (IRGA) is used to continuously monitor CO2 content in the purge gas. The preparation of the molecular sieve cartridge for the next use is performed simultaneously and the IRGA reading is used to verify that all sample CO2 has been removed from the sieve, ensuring insignificant carryover of CO2 into the next sample. We present the results of a suite of standards of distinctly different 14C and stable-carbon isotope composition, which we used to confirm the reliability of the new procedure. The new method has considerably reduced the time required to process a single sample from at least 2 hr to less than 40 min, and reduced the minimum sample size by 50%.

Molecular sieves are a promising way to sample and manipulate gaseous samples for radiocarbon analyses. Molecular sieve material can adsorb CO2 selectively, enabling sampling of CO2 from large air volumes in a small amount of adsorbent. The sieve material can be regenerated via heating and reused without removing the sieve material from its container. This results in ease of use and reduced risks of atmospheric contamination. Because sieve container volume is small and can be filled with synthetic air or nitrogen, it does not introduce underpressure to the system under study. Hence, sieves are suitable for many different experimental setups, from collection of CO2 from small soil chambers to atmospheric CO2 collection. The most common sieve material in use for sampling CO2 is the 13X zeolite. For environmental measurements starting this year, we have studied the properties of 13X zeolites in more detail. For reliable 14CO2 sampling, there are several caveats that should and can be avoided. In this contribution, we discuss these caveats and solutions to optimize the molecular sieve sampling process.

At the Seoul National University accelerator mass spectrometry (AMS) laboratory, we are planning to develop an automated sample preparation system for higher throughput of radiocarbon dating. This system will consist of several sections, including a combustion line, CO2 trap, graphitization system, and so on. We usually collect CO2 by cryogenic trapping. However, since handling liquid nitrogen is expected to be rather difficult, we are interested in replacing the cryogenic method with the molecular sieve method for the collection of CO2. In this study, we compare the performance of the cryogenic trapping method and molecular sieve method. Zeolite 13X is used as a molecular sieve, and as test samples we use the oxalic acid standard (NIST SRM 4990C), high-purity graphite powder, and archaeological charcoals. The pMC values and the radiocarbon ages (BP) obtained from samples prepared by the above 2 methods are very similar. We especially focused on the memory effect of the molecular sieve, meaning the CO2 contamination from a previous sample, which can cause errors in age determination. To reduce this effect, we flowed He gas through a zeolite container for several minutes at a high temperature before the CO2 was introduced. By the adding this step, we have obtained more reliable results.

It has been reported that the characteristics of a very old wood charcoal sample are different from those of modern wood charcoal according to its state of preservation (Cohen-Ofri et al. 2006; Rebollo et al. 2008). It can be assumed that these differences may lead to some difficulties when radiocarbon dating very old wood charcoal samples. To investigate this problem, we studied a carbonized trunk of Prunus pendula for. acendens tree buried in lava and found at the Hantan River lava plateau on the Korean Peninsula. The 14C date of this sample was previously measured as >30,000 BP. However, separate 14C results of its outer crust and inner wood showed a considerable difference, exceeding the estimated age differences by tree-ring counting. To study the reason for this discrepancy, optical microscopy and FTIR (Fourier transform infrared spectroscopy) were performed to examine the differences in the structural and chemical states of the samples. For reference data and to expand our understanding of very old wood charcoal, we applied the same analysis tools (AMS, FTIR, FE-SEM, EDS, and optical microscopy) to a variety of wood charcoals and original wood. From these analyses, we noticed considerable chemical changes in the outer crust sample, and this might explain the age discrepancy. Although it seems that the age difference might be due to the digestion of 14C-free CO2 from a volcanic environment, this explanation would not account for such a large value in the age difference.

Direct dating of prehistoric paintings is playing a major role in Paleolithic art studies. Very few figures can be directly dated since the necessary condition is that they contain organic carbon-based material. Thus, it is very important to check the presence of organic carbon-based material in situ before sampling in order to protect the visual integrity of the paintings or drawings. We have tested and compared 3 different portable analytical systems that can be used in cave environments for detecting carbon in prehistoric paintings: (1) a very compact X-ray fluorescence (XRF) system in Villars Cave (Dordogne, France); (2) a portable micro-Raman spectrometer in Rouffignac Cave (Dordogne, France); and (3) an infrared reflectography camera in both caves. These techniques have been chosen for their non-destructiveness: no sample has to be taken from the rock surface and no contact is made between the probes and the paintings or drawings. The analyses have shown that all the animal figures have been drawn with manganese oxides and cannot be directly dated by radiocarbon. However, carbon has been detected in several spots such as black dots and lines and torch marks. 14C results were obtained from 5 torch marks selected in Villars Cave, with ages between 17.1–18.0 ka cal BP. Three methods were used to identify carbon in black pigments or to confirm the presence of torch marks by carbon detection. Thanks to these new analytical developments, it will be now possible to select more accurately the samples to be taken for 14C dating prehistoric paintings and drawings.

Archaeological bones are now routinely dated in many radiocarbon laboratories through the extraction of “collagen.” Methods for “collagen” extraction vary, and several laboratories now apply an ultrafiltration step after gelatinization to extract the higher molecular weight (usually >10 or 30kDa) fraction for dating, thereby removing low molecular weight contaminants. Ultrafiltration has been demonstrated to result in products that are easier to handle and have more acceptable C:N ratios, and in some instances can result in significantly improved (generally older) 14C dates when compared to non-ultrafiltered products from the same bone. Although it has been suggested that ultrafiltration removes potential contaminants such as short-chain degraded collagen and other peptides and amino acids, fulvic acids, and salts, there remains little published evidence to support this. This paper presents data from a pilot study investigating the most suitable techniques with which to study the products of the routine “collagen” extraction procedures employed at the Oxford Radiocarbon Accelerator Unit (ORAU) (modified Longin followed by ultrafiltration). The preliminary data demonstrates that the final product of “collagen” extraction at ORAU appears to be an aggregate consisting of a range of proteins of different molecular weights, including collagen, as well as some other organic matter and inorganic species. Ultrafiltration is removing some, but not all, of the <30kDa fraction from the samples. Further work to investigate the nature of this aggregate and how best to improve the efficiency of “collagen” extraction procedures is discussed.

We investigated the radiocarbon age and stable isotope composition of bioapatite from bone, enamel, and dentine material from 3 different species of extinct mammals in South America. Most samples of Eremotherium laurillardi, Toxodon platensis, and Notiomastodon platensis were collected in natural depressions located in the northeastern Brazilian provinces of Sergipe, Bahia, and Rio Grande do Norte. All samples studied were devoid of collagen, which had decomposed as a result of high microbiological activity in this tropical region. We have instead analyzed the bioapatite fraction of the samples, which was relatively well preserved even in these harsh tropical conditions. The mineral fraction of bone and tooth material does not usually undergo microbiological decomposition but may be exposed to isotopic exchange with environmental carbonates. The problem thus becomes one of separating the diagenetic carbonates without destroying the bioapatite. We offer a technique for removing the secondary diagenetic carbonates by treatment with diluted acetic acid in a vacuum. We also demonstrate that proper pretreatment of bone and tooth samples allows the separation of diagenetic carbonates from bioapatite, as long as the carbon in these samples has not degraded completely. Bone, enamel, and dentine samples from individuals of the 3 mammalian species were dated using this technique and were compared to results by other researchers from the literature. Date ranges for the species presented were in good agreement with prior research. A comparison with other dating techniques such as U/Th and ESR shows the reliability of the treatment described and the feasibility of 14C dating the bioapatite fraction given certain conditions. In 2 cases, we dated bone enamel and dentine samples from the same individuals of N. platensis, with results between 14 and 21 ka. Results from dating samples of T. platensis are between 11.5 and 13 ka. The oldest tissue in both cases was dentine. The dating of enamel and dentine from the same species did not show regular differences; however, more often the dentine material was older. The oldest date, ≃22.5 ka for E. laurillardi, was obtained on the bioapatite fraction of dentine.

Radiocarbon dating of bones can be very useful in archaeological contexts, especially when dealing with funerary deposits lacking material culture, e.g. pottery vessels. 14C measurements of bone samples are usually performed on the extracted collagen residue. The content and the quality of collagen can vary significantly, mainly depending on bone preservation and diagenesis. Generally speaking, environmental conditions such as low pH level of soils, high temperatures, and percolating groundwaters, typical of arid and tropical zones, can affect the preservation of collagen; at the same time, bones recovered in such environments are more likely to be contaminated with carbon from the surrounding environment. Possible contamination of samples can also occur in temperate zones. While low collagen content is a condition we cannot overcome, we can use several chemical and elemental indicators in order to assess collagen quality. Among these, the C/N atomic ratio is considered a good parameter for detecting low-quality collagen and possibly contaminated samples. In a combustion and graphitization setup like that installed at INFN-LABEC, Florence, measurement can be easily performed using an elemental analyzer when combusting the sample prior to graphitization, thus requiring no extra effort (or extra amount of sample) during the preparation procedure. Bone samples recently 14C dated at INFN-LABEC have confirmed that the measurement of C/N atomic ratios can give some indications of the collagen quality. The bone material was collected from 3 necropoles of the Bronze Age period in Cyprus (Erimi-Laonin tou Porakou, Lophou-Kolaouzou, and Erimi-Kafkalla&Pitharka, along the Kouris Valley), an area characterized by environmental conditions that do not favor bone preservation. Samples were treated to extract collagen and measured by accelerator mass spectrometry (AMS). 14C results have been compared with the archaeological evidence, showing some relationship between measured C/N atomic ratios and collagen quality. In particular, when grouping the measured samples according to their C/N ratio, the agreement between 14C dates and archaeological evidence is good or inconsistent when the C/N ratio clearly falls inside or outside the “recommended” range, respectively, with a still reasonable agreement also when it is slightly above the upper limit of that range.

To study the effect of ultrafiltration on the radiocarbon ages of relatively poorly preserved bones in Japan, we analyzed the 14C dates of high-molecular-weight (HMW) gelatin samples and compared them with those of other extracted organic fractions, unfiltered gelatin samples extracted from NaOH-treated or NaOH-untreated collagen, and XAD-purified hydrolysates of animal fossil bones (∼4600 BP; gelatin yield of 2–4%) from the Awazu underwater archaeological site, Shiga, Japan. NaOH-treated, unfiltered gelatins and XAD-purified hydrolysates showed statistically similar 14C ages to those of HMW gelatins. The 14C ages of the HMW gelatins were the oldest and similar to those of wood collected from the same layer as the bones, and the NaOH-treated, unfiltered gelatins gave 14C ages within the acceptable margins of error; therefore, ultrafiltration was effective for accurate 14C dating, while NaOH-treated gelatin without ultrafiltration was also sufficient to obtain accurate 14C dates on the animal bones. The 14C ages of human skeletons (∼750 BP; gelatin yield of 2–11%) from 5 individuals excavated from an archaeological site in Yuigahama, Kamakura, Japan, showed statistically the same 14C ages as NaOH-treated, unfiltered gelatins and HMW gelatins within the margins of error, although HMW gelatins were likely to give slightly older ages than unfiltered gelatin with a yield of less than ∼3%. These results indicate that unfiltered gelatins extracted from fossil bones of gelatin yield more than ∼3% can produce accurate 14C ages without the need for ultrafiltration. Ten bone fragments from 3 humans showed the same 14C ages for each individual, suggesting that any bone part from an individual can be used to obtain a representative age. The 14C ages of tooth enamels of 2 individuals were 35 and 70 yr older than their bone ages. Death dates obtained from these age gaps agreed with those determined by morphology.

We conducted analyses to identify the most suitable bone pretreatment protocol to be used by the recently established Radiocarbon Laboratory at the University of Cologne, CologneAMS. In 2 sets of analyses, we determined 14C ages for subsamples taken from 3 14C bone standards (Oxford Mammoth, VIRI I, and VIRI H) complemented by age determinations of 12 unknown bone samples. Our results suggest that the strength and duration of the acid and alkali steps and the temperature of gelatinization might have a larger influence on the obtained ages than the presence or absence of ultrafiltration as a pretreatment step.

This paper reports the results of the application of a calcined bone dating protocol to samples collected from the Sanctuary of Zeus on Mt. Lykaion in southern Greece. The site is a mountaintop ash altar rich in anthropogenic sediments, burned bone, and artifacts offered to the god Zeus. Experiments involving time series hydrolysis measurements were conducted on calcined bones from stratified layers throughout the sequence to determine if any of the samples underwent surface contamination from carbonate exchange with the surrounding sedimentary matrix. It was determined that such exchange was unlikely, but samples were acid-etched before pretreatment as a precautionary measure. Paired samples of seeds, charcoal, and calcined animal bone collected from a sediment column in the altar demonstrate the effectiveness of the calcined bone dating technique in this context. The results of dating indicate that the altar was in use from the Mycenaean period through the late Classical period, though samples were not collected from the upper levels of the site due to possible mixing of surface sediments. Fourier transform infrared spectroscopy (FTIR) measurements were taken and crystallinity index values calculated, confirming that the bone samples are indeed calcined. The results presented here correspond with literary accounts of ritual animal sacrifice from historical texts from the 8th century BCE, including the Homeric epics.

This paper reports the results from applying the Cryo2SoniC (Cryobreaking, Sonication, Centrifugation) protocol to some lime mortars sampled from the citadel of Shayzar (Syria). The overall aims of this project are 1) to use the properties offered by high-precision accelerator mass spectrometry (AMS) radiocarbon dating for the evaluation of absolute chronology with its typical robust time constraints (i.e. 25 14C yr), and 2) to apply the dating directly to the citadel structures in order to prevent possible biasing effects potentially affecting indirect 14C dating on organic materials found at the study site. The analyses presented in this paper have been mainly performed as a preliminary check of the Cryo2SoniC methodology in order to assess its applicability to this study site by comparing observed mortar results with archaeological expectations about the citadel development phasing and charcoals found encased in mortars. Petrographic and mineralogical thin-section analyses by optical microscopy (TSOM), X-ray powder diffraction (XRD), and scanning electron microscopy plus energy dispersive spectroscopy (SEM/EDS) investigations were carried out for characterization of the mortar samples to verify the occurrence of some features, related to their production technology, which may introduce dating offsets. The resulting 14C calibrated ages were in agreement with the archaeological expectations based on type and stratigraphic site reconstructions, in situ inscriptions, and written sources. Such results showed also a general (with 1 exception) statistical agreement among the charcoals and the analyzed mortars simultaneously, confirming the archaeological expectations for the Shayzar citadel. Results presented in this paper indicate good accuracy for the applied procedure for chronology reconstruction and highlight the capability of Cryo2SoniC to further characterize the Shayzar site.

The San Lorenzo Cathedral of Alba is a Romanesque church (rebuilt in Gothic epoch) located in northwest Italy. Since 2007, this church has been subjected to renovations and archaeological excavations that led to the finding of the lower part of the basin and the water drainage pipe of a baptismal font of unknown age. Thermoluminescence and radiocarbon dating have been carried out respectively on some ceramic elements and lime mortar samples used in both the pipe and basin of the font. Thermoluminescence results suggest that some of the bricks may have been reused from previous structures while 14C results suggest that the font was built between the 9th and the 11th centuries AD, most probably in the 10th century AD.

The acid-base-acid (ABA) procedure is a common chemical pretreatment used on most organic matter samples. Although this pretreatment is straightforward, there is no consensus among labs about the optimum strength of the chemicals, or even the temperature, to be used for digestions. Comparisons between 14C results obtained by samples undergoing ABA against other wet oxidations, such as acid-base oxidation followed by stepped-combustion (ABOX-SC) or α-cellulose on wood, have sometimes suggested that ABA does not always remove all contaminating carbon. In addition, if not all ABA protocols are the same, could it be said that one procedure is better than others or comparable to wet-oxidation pretreatments, if rigorously applied? To determine whether 14C-free samples showed any fraction modern carbon (FmC) deviations due to pretreatment strategies, 3 experiments were carried out. The first compared 14C results for wood samples at or near the limit of 14C dating, pretreated with a standard ABA protocol used at UC Irvine's Keck Carbon Cycle Accelerator Mass Spectrometry (KCCAMS) facility, with those obtained from ABA- and ABOX-SC-prepared aliquots of the same samples performed at Australian National University (ANU) in 2001. The second experiment subjected wood samples, ranging from ∼12 ka BP to 14C-free, to 5 selected published ABA pretreatments. Third, we evaluated whether the ABA protocol needs a higher-strength final acid step (particularly important for removing CO2 absorption when samples are submerged in alkaline solutions). We are able to show that rigorous ABA treatments exist that can provide robust, reproducible results for many wood samples that are known to be >>50 ka BP, implying that a lack of control over the procedure's outcome might be sample-related, rather than due simply to inadequacies in the chemical pretreatment.

We present a method for the extraction of dissolved organic carbon (DOC) from water. The method is adapted from Burr et al. (2001) using the basic steps: 1) sample filtration; 2) acidification to liberate and remove dissolved inorganic carbon (DIC); 3) evaporation of the sample to isolate salts that include trace quantities of carbon; 4) combustion of the salts; and 5) purification of the CO2. Two significant improvements have been made to the earlier method. The first is to use wet oxidation with potassium permanganate to oxidize organics in place of the combustion step and the second is the development of a reduction/oxidation purification procedure to remove sulfur and nitrogen oxides that may form during the oxidation step. Wet oxidation has a practical advantage over the previous method because it proceeds at low temperature (70 °C). The original method required quartz vessels to oxidize the salts at 900 °C. At this temperature, salts in the samples formed gases that interfered with the isolation of CO2 and the quartz vessels degraded with each combustion, affecting their structural integrity. The expensive quartz vessels could only be used for a limited number of samples, whereas Pyrex vessels used for wet oxidation are inexpensive and can be used indefinitely.

The blank fraction modern carbon (f) and its mass dependence for the refined technique was determined from repeat analyses of salicylic acid produced from petrochemicals. For samples with a mass m above 0.5 mg, F = 0.0083 ± 0.0011. For samples below 0.5 mg, the blank follows a 1/m dependence as observed for other accelerator mass spectrometry (AMS) 14C measurements (Donahue et al. 1990). The reproducibility of the method is demonstrated using repeat measurements from a variety of samples, including a sample measured with the former high-temperature 900 °C combustion technique. The virtues of the wet oxidation method are that it is economical, produces a low blank, and provides good reproducibility.

We discuss a radiocarbon study of sediment samples collected from Nanfu terrace in western Taiwan. From these, we extracted humic acids (HA) and humin from the very fine and coarse grain-size fractions using a standard acid-alkali-acid pretreatment. The humin extracts were combusted at 400 and 1100 °C by stepped-combustion, to yield a low-temperature (LT) carbon component and a high-temperature (HT) carbon component. We compare the ages of the LT and HT humin fractions to the HA fractions, in samples collected at 2 depths within the Nanfu terrace. As in previous stepped-combustion studies on sediments, we find that the HA ages are the youngest on average, and overlap the LT ages, and that the carbon contained in the HT fraction is always distinctly older than the LT and HA ages. To better understand the relationship between 14C age and combustion temperature, we conducted an incremental stepped-combustion experiment with one of the samples (1E) using 50 °C steps that ranged from 300 to 1100 °C. The 14C results of the stepped-combustion products show a clear division between 2 isotopically identifiable carbon constituents, from carbon released below 400 °C and carbon released above 550 °C. By comparing the δ13C and 14C results, we find evidence for a third carbon isotopic component in the humin that is released when combusted at ∼500 °C.