Stable Isotope Facility

Carbon (¹³C) and Nitrogen (¹⁵N) Sample Preparation

Solid samples must be enclosed in tin capsules for analysis. Small samples, such as leaf disks, sections of root, small insects, or fish scales, that meet the target weight can be encapsulated whole in the capsules. Getting a representative sample of larger samples, like leaves, or coarse materials, such as soils or sediments, usually requires grinding and homogenizing.

The amount of sample required depends on the amount of carbon and nitrogen in the material. A sample should contain between 20-150µg N and 200-2000µg C. Use the Sample Weight Calculator to determine appropriate sample weights.

Target Weights for Solid Samples Your actual weights will depend on your samples' C:N ratios. The Sample Weight Calculator will help you refine the required weight.
Sample Type	Target Weight
Plant Tissue (¹⁵N only)	~3-10mg depending on %N
Plant Tissue (¹³C&¹⁵N)	~2-3mg
Wood (¹⁵N only)	~20-30mg depending on %N
Soil / Sediment	~10-75mg depending on organic matter content
Decaying plant litter	~4-6 mg
Animal, Fish, Invertebrate Tissue	~1mg +/- 0.2mg

For glass fiber filter samples, while the amount of carbon and nitrogen required remains the same, 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. If possible include a few test samples. DO NOT use silver filters. See Tips for more dimension restrictions.

Samples that exceed the target weights may not be analyzed because large samples saturate the mass spec detectors, producing unusable data. The SIF is not responsible for lost samples or poor data due to samples exceeding their target weights.

Organization
1) Organize samples into a clean 96-well tray; do not intersperse empty wells between samples. Group similar sample materials together to optimize sample analysis. Mixtures of sample material may delay your analysis.

2) For small samples, ensure they remain in the wells during shipping by placing an index card (cut to size) or Parafilm over the tray before securing the lid. Do not use adhesive tape to cover the open wells. Tape the lid securely closed using tape on all four sides. Turn the tray over and gently shake to test if samples stay in the wells or if the capsules leak sample material. Re-encapsulate any leaky capsules before shipping.

3) Label the lid of each sample tray with a unique name. Include this tray name in the Sample List. Results will include the unique tray name and well position (e.g., A1).

4) For enriched / tracer experiment samples, arrange samples from low to high enrichment to avoid wide fluctuations in isotope content. Place non-enriched control samples ahead of enriched samples within the same tray. Use separate trays for different enriched and natural abundance experiments.

5) IMPORTANT: 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 visit the USDA-APHIS Soil Circular or visit the USDA-APHIS website.

Supplies
Here are a few part numbers and suppliers that SIF uses on a regular basis. Similar products can be found through other consumables catalogs.

Manufacturer / Part#	Description	Unit
Costech / 041061	Tin capsules for solid samples, 5x9 mm	100/pk
Costech / 041073	Tin capsules for large solid samples, 9x10 mm	100/pk
Elemental Microanalysis / D1008 or D1009	Tin capsules for solid samples, 5x8 mm	250/pk or 100/pk
Electron Microscopy Sciences / 70437-R1	96-Well Plate, Round-Bottom, With Lid	10/pk
Electron Microscopy Sciences / 70437-R5	96-Well Plate, Round-Bottom, With Lid	50/cs
BD Falcon / 351172	96-well Microplates, clear, flat-bottom with lid	50/cs
BD Falcon / 351178	48-well Cell Culture Plate, nontreated polystyrene, flat-bottom with lid	50/cs

Shipping
Please read and follow the instructions carefully to ensure safe transit and appropriate handling of your samples.

1) Please complete the online Analysis Order Form and Sample List for your samples and email these forms to sif@ucdavis.edu. Please include a printed copy of these forms with your samples. The SIF uses this form to track your samples and to contact you regarding receipt of samples, data, and invoicing. For mixed analysis requests, we require the completion of a separate form for each type of analysis.

The sample list should include weights where appropriate. If more rows are required in the sample list, simply add the rows and continue the numbering in column A.

Also, please include:
- A general description of the material being analyzed including approximate elemental composition.
- The expected range of isotopic composition enriched material.

2) If you are shipping soils from outside USA, please contact us to receive a copy of our Soil Import Permit to include with your shipment.

3) Carefully package the sample trays to protect them during shipping. Single trays should be wrapped with multiple layers of bubble wrap and can be shipped in a padded envelope or box. Multiple trays should be banded or taped together and shipped in rigid box filled with packing material. Desiccants, such as Drierite, should not be included with samples unless contained within a spillproof, separate package.

Failure to properly package and protect trays often results in sample loss during shipping.