Carbon and Nitrogen in Solids

Tips for Preparing Your Large Bulk Difficult Combustion 13C & 15N Solid Samples - Soils, Sediments, Filters, Wood, and Carbonates

Analysis of biogenic carbonates by EA-IRMS versus GasBench-IRMS
The SIF does not regularly analyze biogenic carbonates by EA-IRMS due to poor combustion of the inoganic matrix resulting in poor data precision. Instead, please consider the analysis of biogenic apatite and carbonates by GasBench-IRMS.

For geologic carbonates, please try contacting the Center for Stable Isotope Biogeochemistry at UC Berkeley.

If you need to see both the inorganic and organic C of your solid sample material, then you would need to submit two solid samples for EA-IRMS: 1) one untreated sample packaged in tin (Sn) capsule, and 2) one sample that has been acid fumigated/acid washed to remove carbonate and encapsulated in silver (Ag) capsules.

Acid treatment is known to skew the 15N isotope signal. Contact us prior to preparing carbonate samples.

Removing carbonates from calcareous soils and sediments before organic 13C analysis
Inorganic C in the form of carbonates can interfere with the measurement of organic 13C in soils. In low carbonate materials (less than ~3% carbonate), you can remove inorganic C by acid fumigation. Weigh soil samples into silver capsules (tin is corroded when exposed to acid) and arrange samples in a 96-well tray. Add a small amount of water to each open capsule to wet the soil. Place the whole 96-well tray in a desiccator containing a beaker of concentrated (12M) HCl. Carbonates are released as CO2 in 6 to 8 hours. Dry the samples at 60 °C and carefully crimp-seal the capsules. The capsules become brittle after drying, resulting in leaks; be careful not to lose material when crimping. We recommend placing the whole capsule into a new tin (Sn) capsule and crimp it closed. The additional tin capsule is an important combustion catalyst, so it is advantageous to use tin capsules for re-encapsulating leaking samples.

High carbonate samples must be pulverized and acid washed until the material stops bubbling. Rinse thoroughly to remove residual acid and hygroscopic salts, and encapsulate in silver (Ag) capsules. The formation of hygroscopic salts does mean the material can be very difficult to keep dry. Please ship acidified samples with a fully sealed desiccant pouch (loose desiccant on the 96-well plate is a contaminant). Due to hazardous waste disposal, we strongly advise against shipping blue desiccant that contains cobalt chloride (CoCl2). Please use a desiccant that is safe for standard garbage disposal.

For more information on acid fumigation to remove carbonates, please refer to: Harris, D., Horwath, W.R., and van Kessel, C., 2001. Acid fumigation of soils to remove carbonates prior to total organic carbon or carbon-13 isotopic analysis. Soil Science Society of America Journal 65: 1853-1856.

Use large tins for bulky samples
As with small bulk samples, the amount of carbon and nitrogen should be between 20-150 µg N and 200-2000 µg C for glass fiber filter (GF/F) samples; however, the sample weight guidelines do not apply. Please minimize the amount of filter in each sample. This can be accomplished by increasing material loading and using only a portion of the filter or by cutting away the annular portion of the filter which contains no material. The largest whole filter that can be analyzed is 25mm or equivalent (i.e. half of a 47mm filter), and the largest encapsulated sample dimension that can fit into our analyzer is 8 x 8 mm. If possible include a few test samples. DO NOT use silver filters without prior coordination with the SIF. See Tips for more dimension restrictions.

Large 9x10 mm tin capsules are helpful for encapsulating bulky items, like filter disks, which must be tightly packaged to maintain a compact form in the autosampler. The final sample diameter must be no larger than 8mm wide X 8mm tall. If samples are too large for a 96-well tray, organize and ship them in a 24 or 48-well tray instead. Please do not force large samples into a 96-well tray, they will expand during shipping and we will not be able to extract these samples from their wells.

Include replicates to check precision, especially for complex matrices
The SIF runs calibrated standards to confirm the precision of our analyses. Client replicates are recommended to check the precision of your samples, especially for samples that exceed our detection limits. The number of replicates you provide is at the researcher’s discretion as we understand that replicates incur added cost. The SIF recommends providing a few replicates per batch (e.g. 1 replicate per 8-12 samples) with more replicates recommended for more complex matrices (e.g. 1 replicate per 6-12 samples for filters, soils, etc.).

Soil samples will require our Soil Permit prior to shipment
Please label all trays containing soil, forest litter, wood or plant compost, humus, and earthworm castings. Most southeastern soil2002_0.pdf states and foreign countries have regulations regarding soil movement to prevent the spread of agricultural pests. The SIF is responsible for proper disposal of any imported and restricted samples that we receive. For more information please read the USDA-APHIS Soil Circular or visit the USDA-APHIS website.


Tips for Large Bulk Samples
- Don't over-fill capsules. Excess filter paper can be trimmed off to reduce volume.
- Don't contaminate samples by handling with bare hands

Above are examples of very large samples (from left to right):
~6 mm tall X 5 mm wide, this is an example of a "good" large sample.
~6 mm tall X 6 mm wide, this sample is too wide for a 96-well plate. It will fill the well of a 96-well plate, making it hard to retrieve. Use a 48 or 24-well plate instead.
~12 mm tall X 5.5 mm wide. This sample is too tall and will clog our autosampler. Reshape to dimensions no larger than 8 mm wide X 8 mm tall.
-Over-stuffed with GF/F filter, this sample has burst. This may occur as you are closing your samples, or later during shipping as filter tends to expand after being compressed. Trimming off excess filter will reduce the volume of filter paper being packaged. Re-encapsulate samples with exposed or leaking sample material, the extra tin (Sn) is OK!


Other helpful tips:

How to encapsulate samples

Use KHSO4 for ammonia diffusion traps

Avoid contaminating your samples with packing materials

Keep enriched samples separate from natural abundance samples