NOSAMS

Note about δ¹³C analysis: If you have already measured the δ¹³C for your samples and plan to submit those values to us, or are considering using an assumed value, please consider letting us measure it from a split of CO₂ from your sample as well. We'd like to encourage you to let us measure δ¹³C here as a low-cost check for quality - it is useful for evaluating an unexpected ¹⁴C result.

Approximately 0.5 gram of bone material is required to extract enough collagen for a standard AMS sample. This is approximate since conditions for preservation vary and generally, the older the bone, the less collagen is extracted. Due to the labor-intensity of the extraction, if an inadequate amount of collagen is obtained from a sample for AMS, we will bill for partial processing up to the point of the collagen extraction.

Currently we are sending our bone samples to an outside specialist for the extraction of collagen, and in turn we combust the collagen and convert to graphite here in our Sample Prep Lab. The collagen extraction method used is referred to as EDTA (ethylenediaminetetra-acetic acid ). It takes generally no more than 30 days to get the collagen and we try our best to keep the total turnaround time to a minimum, but in some cases, the decalcification of bone can take longer. For instance, if the bone is poorly preserved or contains a lot of humic material or dirt, the process may take a few weeks longer than the average turnaround. Process used Organic Combustion.

The carbon content of charcoal can vary significantly. However, under good conditions, 40% is a reasonable estimate of the organic carbon by weight, therefore approximately 1 milligram of clean charcoal in good condition should suffice for a standard analysis and a minimum of approximately 0.05 milligrams for small sample analysis.

Often, charcoal becomes broken and disseminated in surrounding soil matrixes. Separation or purification of the charcoal component may be as simple as scraping away the outer surfaces, but if disseminated, can be performed by gently cleansing samples, sieving and using a wet "picking" brush under a microscopic or magnifier to collect the charcoal fragments. Then, if further cleaning is necessary, gently sonicate samples with distilled water and carefully draw off the supernate. Repeat until clean. Dry, weigh and transfer to clean glass vials. If a mixture of disseminated material is submitted, then the mixture will be combusted; our procedures do not include hand-picking out the fragments of charcoal.

If your sample weighs less than 0.7 milligrams and you request small sample analysis, keep in mind that the transfer of material, the pre-treatment of charcoal and a 10% split of CO₂ for in-line stable δ¹³C analysis will further reduce the available carbon. You may request to forego pretreatment (on the subittal form) or assume a δ¹³C value in order to conserve carbon. Process used Organic Combustion.

Compound-specific
These are typically collected by submitters with a PCGC, or preparative capillary gas chromatographic system (supplemented with a liquid-chromatographic system). Compound-specific samples are usually small samples (~ <300 ug C) requiring a solvent transfer to a combustion tube. Techniques to handle such small samples were initially developed at NOSAMS specifically to aid the development of compound-specific radiocarbon analysis of compounds like fatty acids, sterols, plant waxes, lignin phenols, PAHs, PCBs, and lipids.

Training is available for the PCGC technique. Compound-specific samples may be prepared and isolated by NOSAMS staff with fees determined upon request. (contact NOSAMS) Process used Organic Combustion.

Dissolved Organic Carbon
Currently we do not extract Dissolved Organic Carbon (DOC) in our Sample Prep Lab; these are submitted pre-processed/extracted by the investigator and we directly combust. Process used Organic Combustion.

Clean all non-plant/wood material from the sample using distilled water and thoroughly dry in a low temperature oven (50º C). Weigh and place in a clean, labeled vial. A general rule-of-thumb is to estimate 40% carbon by weight for plant/wood or charcoal. Some weight is potentially lost due to pre-treatment of plant/wood which involves the base extraction of mobile humic and fulvic substances and acid removal of inorganic carbon. If stable isotope analysis is requested, we will take approximately a 10% split of the CO₂ produced for in-line analysis.

If the sample is clean and in good condition, you could estimate that a regular-sized sample would weigh a minimum of approximately 1 mg and that a weight in the range of 0.25 - 1 mg would likely require small sample techniques. If your sample falls within this range, please indicate on the Submittal Form (question 4) that we may use these techniques if necessary. Process used Organic Combustion.

The organic carbon content of sediments vary considerably. We must know the measured % organic carbon content before we can gauge how much sample to combust. Too much material can cause the combustion tube to explode and sample loss; too little material will result in an insufficient amount for AMS analysis. Please indicate on the submittal form whether you have measured the %OC or not. If not, we will determine it for a small additional fee.

Sediment (Corg) samples typically undergo the acid pretreatment only, to remove inorganic carbon before combustion. We also offer vapor-phase acidification when requested. If your sediment contains plant material like peat, then we recommend the same treatment as plant/wood samples to remove any mobile humic or fulvic components. If the sediment contains a peat component, please indicate your preference for acid only or an acid-base-acid series of leaches on the submittal form.

Submit dry sediment samples in well-labeled, clean glass or plastic containers. We assume samples are homogeneous. Some submitters dry and grind sediment samples prior to submission to ensure homogeneity. Process used Organic Combustion.

Aerosols (total organic)
Particulates collected on *quartz* filters can be combusted at high temperature (850 deg C) together with the sample. If pyrex filters are used, the temperature must be reduced (550 deg C) which could reult in incomplete combustion of total organic carbon. Please provide the carbon loading (in milligrams C) in order for us to assess how much of the sample/filter to pack into a combustion tube. It's best to receive the filters flat rather than packed or rolled to fit into vials or containers. Past clients have used cleaned/baked aluminum foil to double wrap the sample and filter, freeze and send to us. Pre-combust foil at 550 degrees for one hour before using. Aerosols are kept cool and dry to avoid bacterial growth.

Other -Textiles, black carbon etc.
Please contact us regarding the particulars of other types to determine handling and fees. Process used Organic Combustion.

Sample Types - Inorganic Carbon
Inorganic carbon samples will be weighed and directly hydrolyzed in our Sample Prep Lab.

Corals, like tree-rings, and sometimes molluscs, have annual growth bands and can be sampled according to the years of growth. Optimal sample size for carbonates is approximately between 8 and 12 milligrams. Carbonate weights in the range of approximately 1 to 2.5 mg require small sample techniques. If you expect your sample falls into this category, please indicate whether we may use small sample techniques on the Submittal Form (question 4.)

To estimate the milligrams of carbon in carbonate, use the formula mg C = mg CaCO₃/8.33 then multiply by 0.9 to account for impurities. When requested, a 10 % split of the CO₂ generated is taken for in-line stable isotope measurement. Process used Hydrolysis.

A minimum of 4 milligrams of clean forams is required for a regular-sized AMS sample; a subsample may be taken if more than 12 mg is submitted. If pure, a 4 mg sample will conservatively yield approximately 430 micrograms of carbon (0.004g * 0.9 yield / 8.33 MW carbonate). When requested, a 10% split of the CO₂ generated is taken for in-line stable isotope measurement (430-43 µg ). Carbonate weights in the range of approximately 1 to 2.5 mg require small sample techniques.

If there is sediment on and in the forams that contains carbonate of a different age than the forams, it will skew the radiocarbon result. Some submitters sonicate forams in a 3% peroxide and sodium hexametaphosphate solution and rinse with DH₂O to clean tests. Take care to inspect the sample immediately prior to submitting and to remove anything that is not a foram, including fibers, hair or quartz grains. The smaller the sample, the larger the potential impact of small bits of contamination on the isotope concentration. Process used Hydrolysis.

Sea, lake, pond, ground or pore water.

Protocols for collection of DIC samples can be found here (MS Word text only) and here (also in MS Word including photos).

Beginning with sample collection, it is extremely important that all of the materials coming into contact with the water are as ¹⁴C-free as possible. Post-collection biological activity can alter the carbon isotopic concentration of the samples. Addition of a saturated mercuric chloride solution will kill all bacteria (typically used for seawater samples), but this may not be appropriate for your sampling situation. Other poisons should be discussed with us if you choose not to use HgCl₂. If the sulphur content in the water is greater than that of standard seawater, then you may need additional poison.

DIC Sample bottles:
Our preferred DIC sample collection vessel is a 500 ml borosilicate glass bottle with a high-quality ground-glass stopper.The stopper is lubricated prior to collection with Apiezon grease to prevent exchange with the atmosphere. NOSAMS has an automated water stripping vacuum line system with probes designed to fit a specific bottle opening. If the samples arrive with an opening that cannot accept our probes, the water must be transferred and this is less than ideal. We may be able to supply bottles for your sample collection - please contact us for more information and refer to the collection protocols for full specifications. A shipping account number will be required to return sample bottles that differ from these specifications.

In order to handle a water sample, we must know the DIC concentration. We need to know whether there will be too much CO₂ evolved for our vacuum system to accommodate. The water stripping lines are automated and run unattended overnight. They were designed to accommodate a range of concentrations typically found in a liter of seawater (approximately 2 mmol/kg). One of the highest concentrations we've handled (from groundwater) was about 14 mmol/kg and that required some creativity (one liter of water weighs 1 kg). Process used Water Stripping .

Mollusc


	Arctica islandica bivalve next to an example of AMS-sized sub-sample on finger.

Mollusc samples are typically quite large and require subsampling to prepare an AMS sample. When there is the luxury of excess material, use it to prepare a pristine portion of the inner shell by scraping, cutting or grinding away the sometimes chalky outer portions of the shell that are most susceptible to recrystallization. Consider sampling across growth-bands for a representative sample, or using the inner or outer year growth parts only for a more age-constrained sample.

A minimum of 2.8 milligrams of clean shell is required for a regular-sized AMS sample, 8 milligrams is optimal. A subsample may be taken if more than 12 mg is submitted. If pure, a 2.8 mg sample will conservatively yield approximately 300 micrograms of carbon (0.0028 g * 0.9 yield / 8.33 MW carbonate). Carbonate weights in the range of approximately 1 to 2.5 mg require small sample techniques. If your sample is near this range, please indicate on the Submittal Form whether we may use small sample techniques (question 4).

Treating carbonates with a mild acid leach prior to submission is not recommended because this procedure is best done immediately prior to the full acid hydrolysis. Over time, an etched surface may adsorb CO₂ from the air. If there is enough material and you want to remove the surface portion of your shell, an acid etch/leach may be requested on the submittal form under question 8. Process used Hydrolysis.

Sediment (carbonates)


	Ground, dried sediment.

The inorganic carbon content of sediments can vary considerably. We need at least an approximate idea of the %CaCO₃ of sediment before we can treat it. Without this information, we will not be able to process the samples.

Submit dry sediment samples in well-labeled, clean glass or plastic containers. We assume samples are homogeneous. Some submitters dry and grind sediment samples prior to submission to ensure homogeneity. Process used Hydrolysis.

We may require that you send a "contamination-check" sample of CO₂, so we can verify that your laboratory is ¹⁴C-free, before we routinely process your gas samples in our Sample Prep Lab. Contamination check samples are prepared in a specially isolated area so as not to (potentially) contaminate samples from other investigators.

We offer free analysis of one blank and one modern standard for submissions of CO₂ in batches of 10 samples or more (that would be >= 12 actual samples submitted) and charge half price for the standards submitted with batches of less than 10 gas samples. It is good practice for submitters to include a modern and dead gas sample to assess the reliability of lab techniques used to prepare a sample to CO₂.

We recommend submitting CO₂ in 6 or 9 mm (outside dimension) flame-sealed Pyrex or quartz tubes with a targeted sample size of 80 micromoles of gas. Small samples are in the range of 8 - 23 µmol and regular sized samples approximately 24 - 350 µmol. Typically a portion of the gas is transferred for on-line stable isotope analysis (δ ¹³C). A fee will be charged for archival of large sample splits. We prefer the 6 mm OD sized tubes because they tend to crack more cleanly; the 9 mm tubes can hold larger volumes and may be easier to flame-seal, but tend to shatter in the cracker. We need to know the amount of gas submitted, preferably in umols, before we can accept CO₂ samples.

Please aim for a sealed pressure of less than 2 atmospheres and a flame-sealed tube length of 6-7 inches. Label the with attached tape or paper (tightly attached) or use a permanent black marker to label the ampoule. Process used Gas Sample.

Graphite

Photo of graphite samples, or pure carbon and Fe catalyst ready for pressing into an AMS target.
Potential submitters of graphite should first contact us for details on packing, fees and turnaround time before sending graphite samples to NOSAMS.

Generally, as an initial test, we ask for 10 to no more than 15 loose graphite samples in a batch to determine whether we can successfully analyze your graphite. These should all be primary or secondary standards and blanks of known ages. We routinely analyze graphite prepared using Fe catalyst in a ratio of approximately 1:1, Fe to carbon by weight. Our suggested target weight for graphite on Fe is approximately 1 milligram. Special arrangements are required for analyzing graphite samples weighing less than 0.4 milligrams. A client is allowed up to 30 free test samples to establish that we can successfully handle and analyze them, after that, the normal fees apply. Based on the performance of the test batches, we will decide whether we can accept unknowns for a fee. For every five unknowns, one standard (OXI or OXII) is required. So, n/5 + 1 additional standards are requested to bracket all unknowns where n is the number of unknowns. We typically analyze 2 process blanks per process type up to 4 per wheel free of charge, any more will incur the normal fees. A unique graphite number should be assigned to each graphite sample submitted and that number appear on the sample container.

When we can successfully analyze loose graphite from a client, we can progress to receiving pressed samples if so desired, again by starting with test batches of 10-15 targets. Process used Target Press.

Contamination check and swipe samples

Collecting a swipe sample.

Swipe samples are used to check surfaces for above natural levels of ¹⁴C. Swipes and other materials suspected of elevated radiocarbon content are analyzed in a separate preparation lab using a sealed-tube graphitization procedure to prevent cross-contamination. Fees for swipe or contamination check analysis may be waived if made in conjunction with regular sample submission.

To collect a swipe sample:
Pre-clean quartz filters by baking at 900^o C for 2-3 hours. The preferred filter is 25 mm quartz but other sizes and glass fiber filters are accetable if prebaked and indicated.
Choose areas to swipe that have seen a lot of handling such as doorknobs, ovens, refrigerators, fume hoods and counter tops. Wear disposable gloves and dispose of them after each swipe and replace to avoid transferring contamination to the next sample. A single swipe is sufficient for each surface. Place all your tools and supplies on a disposable work surface such as clean paper, aluminum foil or paper towel. Throw this away and replace in each new sampling location.
Moisten pre-baked filter with HPLC grade or better isopropyl alcohol. Gently rub the filter over the area to be swiped being careful to avoid breaking up the brittle filter if possible. Place the swipe in a prebaked glass container labeled with the name or location of the object swiped, the date and any other pertinent information.. Prepare at least one blank swipe per batch of 10 by moistening with the alcohol and placing into the same container without touching or swiping any surfaces. Submit as you would a normal AMS sample.