Stable Isotope Facility

Sulfur (³⁴S) Solid Sample Preparation

Samples should be thoroughly dried prior to analysis (e.g. 70°C, 24h), as the presence of sample water is especially troublesome for ³⁴S analysis. Samples that must be stored for a long period prior to analysis should be placed in a desiccator.

Dry, solid samples must be enclosed in tin capsules for analysis (see sample encapsulation tips). 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, requires grinding and homogenization.

Oxidant must be also be added to each tin capsule during sample preparation. The SIF uses niobium pentoxide (Nb₂O₅; 0.2-0.5mm grain size, Elemental Microanalysis). While other oxidants are suitable, in order to maintain ¹⁸O homogeneity between samples and standards, the SIF highly recommends that researchers prepare samples using the same oxidant type (Nb₂O₅) and supplier (Elemental Microanalysis).

Organic samples generally range between 0.1% and 1.5% sulfur by dry weight (animals, 0.8-1.2%S; plants, 0.1-0.4%S). Inorganic-organic mixtures, such as soils and sediments, are more variable (0.01-1%S). A properly prepared sample should contain between 15-25 µg S. If the sulfur content of your samples is unknown, we suggest that you send a small set of test samples to verify S content prior to preparing samples for submission.

Organization
1) Organize samples into a clean 96-well tray; do not leave empty wells.

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 samples, arrange samples to avoid wide fluctuations in isotope content. Place non-enriched samples ahead of enriched samples within the same tray, or place non-enriched and enriched samples in separate trays.

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, non-treated polystyrene, flat-bottom with lid	50/cs
Elemental Microanalysis / B1291	Niobium pentoxide, 0.2-0.5mm	100g

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 of enriched material.

2) If you are shipping soils from outside the 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 sample material often results in sample loss during shipping.