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

Basic Sample Preparation

Dry your samples
Solid samples should be dried in an appropriate oven at 50-60 °C overnight, and up to a few days, until the sample is considered dry. "Over dry" samples will "gain weight" when it is weighed on a microbalance, as it absorbs moisture from the air. The material should be allowed to acclimate to the ambient humidity for a few days if the material is too dry. Moist samples will be sticky, clumpy, difficult to grind, or may "lose weight" when it is weighed on a microbalance as it loses moisture to the air.

Grind, weigh, and encapsulate your samples
Small samples that meet the target weight, such as leaf disks, sections of root, small insects, or fish scales, can be encapsulated whole into tin (Sn) capsules. Getting a representative sample of larger samples, like leaves, or coarse materials, such as soils or sediments, usually requires grinding and homogenizing.

All samples must be enclosed in tin (Sn) capsules for analysis. The tin is an important combustion catalyst. While the use of silver (Ag) capsules may be necessary for acid fumed materials, the use of any alternative capsule (e.g. nickel (Ni) capsules) is unacceptable.

The amount of sample to be weighed depends on the amount of carbon and nitrogen in the dried material. A sample should contain between 20-150 µg N and 200-2000 µg C. Our limit of detection with a long-term standard deviation of 0.2 ‰ is 20 µg N and 100 µg C in a natural abundance sample.

Use the Sample Weight Calculator to determine appropriate sample weights.
 

Large bulk samples, such as filters, soils, and sediments, are considered difficult combustion materials, and may require additional preparation.

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.


Organize your samples
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. Please use our sample list to organize your samples, and to convey important sample information to the SIF.

2) For small samples, ensure they remain in the wells during shipping by placing an index card (cut to size) over the tray wells before securing the lid. Do not use Parafilm or adhesive tape to cover the open wells as the adhesive may contaminate your samples. 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, check for a bulging tray lids due to evaporation rings that are incorporated in the 96-well plate design. If the capsules leak sample material, re-encapsulate the sample in an additional tin (Sn) capsule. The additional tin material is OK as it acts as a combustion catalyst.

3) Label the lid of each sample tray with a unique name (maximum of 16 alphanumeric characters). Results will be reported using the unique tray name and sample well position (e.g., A1). For clients shipping multiple sample sets over the course of a year, please name the entire year's worth of trays with unique names. For example, January 2014 submit Trays #1, 2,& 3. In February submit Trays #4, 5, & 6. Please avoid sending multiple trays named "Tray#1" or "Project 1". We enjoy creative tray names!

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 read 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.
 

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

1) Please initiate an order online through PPMS; detailed instructions are here.

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.