Stable Isotope Facility ISOGOT

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

All samples must be dried thoroughly before packing and analysis (freeze drying for soils/sediments). Grind sample to homogenise (e.g. in an agate mortar) and weigh the sample into tin (Sn) capsules (see below) – tin is crucial for the combustion process. Do not over-fill the capsules as they may break, and sample mases will be inaccurate.

Close the capsule using clean tweezers/forceps, making sure the capsule is as round/smooth as possible and store in a 96-well plate until analysis. The packed samples should be able to move freely in the well – samples that are too large will not be analysed as they will get stuck in the autosampler. Isotope analysis will only be as good as your sample preparation and weighing! 

All samples should contain a similar elemental amount. Ideally samples for CN analysis contain >100 μg N (min. 30 μg), but not more than 2000 μ C. If samples contain more than 2000 μg C, please inform the ISOGOT manager. If elemental composition (e.g. ug or % C and N) is of interest, exact weight must be provided. 

Useful information is also found on UCDavis Stable Isotope Facility website

Approximate weights per sample type

• Plant tissue (leaves, roots, seaweeds): 3-4mg 
• Soil: 35-70mg 
• Sediment: 20-40mg 
• Animal tissue: ~1mg +/- 0.2mg 

See also the UC Davis sample weight calculator 

Additional information for certain types of sample

Enriched samples 

Please declare samples with enriched (15N and/or 13C) contents in the sample list excel file so we can avoid carry-over to natural abundance samples. Arrange samples from low to high enrichment, unenriched samples first; ideally avoid combining natural abundance and enriched samples in one tray 

Removal of carbonates for TOC analysis (e.g. from sediments or filtered particles) 

Sediment 

• Weigh dried sample into a SILVER capsule (tin capsules will disintegrate under acid treatment). 
• Leave capsules open in a thick-walled well plate in 12M HCl fumes for 6-8h 
• Dry at 60deg 
• Wrap silver capsule in tin capsule and transfer to 96-well plate 

Samples on GFF filters (e.g. plankton) 

• Filters (GFF) must be pre-combusted (450oC, 6h) before filtration 
• Filter required volume to meet above C and N requirements 
• Dry filter at 60oC overnight 
• Treat in 6M HCl fumes for 12h 
• Dry at 60deg 
• Fold filter paper into tin boat and transfer to 96-well plate Recommended: Tin boats 6 x 6 x 12 mm | 500/pack www.saentis-analytical.com SA22137419 (OEM-parts: 200007074 / 22 137 419)