Tips for Preparing Your Large Bulk Difficult Combustion 13C & 15N Solid Samples - Soils, Sediments, Filters, Wood, and Carbonates
The SIF does not regularly analyze carbonates
The SIF does not regularly analyze carbonates due to poor combustion and poor data precision. We recommend contacting the Stable Isotope Laboratory (subtle name difference) at UC Davis to analyze your carbonate samples.
If you need to see both the inorganic and organic C of your sample material, then you would need to submit two samples, one untreated and packaged in tin (Sn) capsule, and one that has been acid fumigated/acid washed to remove carbonate and encapsulated in silver (Ag) capsules. Both would be analyzed for C&N and would cost US$10 for each encapsulated sample. 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. Remove inorganic C by acid fumigation. Weigh soil samples into silver capsules (tin decomposes 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.
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 20-150µg N and 200-2000µg 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 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
- Don't contaminate samples by handling with bare hands
|Above are examples of very large samples (from left to right):
~6mm tall X 5mm wide, this is an example of a "good" large sample.
~6mm tall X 6mm 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.
~12mm tall X 5.5mm wide. This sample is too tall and will clog our autosampler. Reshape to dimensions no larger than 8mm wide X 8mm 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:
e-mail: firstname.lastname@example.org | phone: 530-752-8100 | fax: 530-752-4361
UC Davis Stable Isotope Facility | Department of Plant Sciences
One Shields Avenue | Davis, California, 95616 | USA