Carbonate sample preparation

This is a guide for preparing samples for carbonate-iRMS analysis, including how to document, package, and ship samples to UCSC SIL for analysis.

Before starting a project, please consult UCSC SiL to determine project feasibility and determine specific preparation protocols. In person training will be provided for UCSC users.

Carbonate sample amount

Kiel IV-MAT 253 routine sample amounts are ~10-100 µg weight equivalent CaCO₃. Samples significantly larger than ~200 µg weight equivalent CaCO₃ should be subsampled to ensure efficient analysis without fractionation. Samples smaller than 5 µg CaCO₃ measured with the Kiel IV-MAT 253 do not yield useful isotope ratio data.

Weights of foraminifera samples may be estimated. For example, if shells for a given taxa are known to weigh ~20 µg each, then instead of weighing each sample individually, 3 shells may be simply collected for each carbonate isotope sample, yielding ~60 µg CaCO₃ per sample. Precise knowledge of individual sample weight is not important for accurate carbonate isotope ratio analysis.

Note that fine-grain samples of drilled, ground, or powdered material will typically be subsampled at UCSC SIL by weighing prior to analysis. Quantitative recovery of fine-grain material from vials after shipment is practically limited. If fine grained material is not sample limited, please ship ~1 mg more sample than is necessary for analysis. This amount may be estimated visually, as this aliquot will be subsampled precisely at UCSC SIL. If fine-grain material is sample limited, as is typical for drilled otolith or speleothem, please see instructions for preparing samples in aluminum foil envelopes in the description of sample packaging below.

For bulk marine sediments, ~100 µg is often a reliable sample size. For samples with unknown wt%CaCO₃, this sample amount yields enough CaCO₃ for a carbonate isotope ratio measurement for any sample >10 wt%CaCO₃ without compromising the efficiency either carbonate acidolysis or the dynamic range efficient and accurate measurement by the Kiel IV. Samples with <10 wt%CaCO₃ require appropriately larger samples. Please include information about wt%CaCO₃ if known. As discussed above, please ship ~1 mg more sample than is necessary for analysis

For well-preserved apatite from tooth enamel, bone, or dentine to be measured with the Kiel IV, a reliable sample size range is 700-800 µg of treated material. This amount usually represents an optimum of CO₃ yield versus efficient sample acidolysis. Fossil samples may require a larger sample size. Sample up to ~1500 µg can be measured efficiently.

Carbonate pre-treatment

For proper subsampling and pre-treatment protocols, it is generally advisable to consult methods from peer-reviewed literature relavent to your specific field of research.

Enamel, dentine, and bone samples typically require pre-treatment prior to carbonate isotope ratio analysis. The sample amounts recommended above are with respect to weight after treatment. Please follow the links for example protocols for pre-treatment of tooth enamel and a protocol for pre-treatment of dentine or bone.

Carbonate sample documentation

When you submit your samples to UCSC SiL for analysis, you need to share a sample information spreadsheet file that includes sample IDs in one column. This file can be shared as a Google Sheet, Excel file, or CSV.

Please keep all physical documentation. Do not ship physical notes to UCSC.

Carbonate sample packaging and shipping

It is always good practice to consult UCSC SiL before preparing and packaging samples for shipment.

Carbonate samples prepared for analysis at UCSC are prepared differently than samples that are shipped to UCSC SiL. Samples prepared on site may be prepared one run at a time directly into glass Kiel IV vials on the day before analysis. Samples prepared at UCSC more than one day before the day of measurement may be prepared multiple runs at a time in clean stainless steel boats organized in 30 sample trays. Please refer to carbonate iRMS steel boat notes for instructions to help you properly prepare your samples.

Foraminifera and other granular samples like shell fragments can be prepared for shipment either by mounting on micropaleontology slides or by transferring into labeled Eppendorf microcentifuge tubes. You may package samples in screw-top glass vials, but you must be absolutely certain to tape the tops on before shipping or samples will be lost.

Fine grain material with excess sample like bulk marine sediments, bulk carbonate rocks, and bone or tooth apatite samples should be prepared for shipment by transferring into labeled Eppendorf microcentrifuge tubes. Alternatively, the custom aluminum foil packets recommended for small fine grain samples will also work well for larger amounts of material.

Fine grain material without excess sample is sample limited and must be packaged to maximize recovery by UCSC SiL after shipment. This is typical for drilled speleothem and drilled otolith and may also apply to some specimens of bone or tooth apatite. For this application, UCSC SiL recommends either preparing samples in Eppendorf microcentrifuge tubes or preparing samples in custom aluminum foil packets. Fine grained material will be transferred to analysis vials via dry centrifugation. Please test which preparation scheme is appropriate for your sample type before preparing all of your samples.

Preparing aluminum foil packets for fine-grain carbonate sample material

Properly packaged carbonate samples are generally safe and ready for shipping with minimal packaging. We recommend wrapping samples in a single layer of bubble wrap or other padding and shipping in a small flat-rate box or envelope.