Carbon and Nitrogen

  • δ13C and δ15N values of solid materials are determined by continuous flow (CF) dual isotope analysis using a CHNOS Elemental Analyzer interfaced to an IsoPrime100 mass spectrometer. Long-term external precision for C and N isotope determinations is  ± 0.10‰ and  ± 0.20‰, respectively.
  • Sample preparation: Solid samples should be ground to flour like consistency (a fine, 200 mesh, powder with no visibly different particles with naked eye) and weighed out in tin capsules on a six-place microbalance. The sample weight should be recorded if total % N or % C determinations are required. We recommend that you use either 4×6 mm (part #041070) or 5×9 mm tin capsules (part #041061) from Costech Analytical Technologies, Inc. (http://www.costechanalytical.com/). Do not handle the boats with your bare hands (always use forceps) and make sure that the samples are free of any other material containing carbon and nitrogen. Tin capsules should be folded and compressed into a compact cylindrical or spherical shapes with a maximum dimension of 6 mm. Entire objects of small mass such as insects, sections of root, leaf disks, can be packaged whole, but check with us first before packing these. Remember to remove carbonates from calcareous soils before analysis for SOM 13C.
  • Sample size: Samples for N measurement should contain 30-300 μg of N and samples for C measurement should contain 0.5-4 mg of C. Samples outside these size ranges can be analyzed but require a specialized analysis method. Contact us first to discuss the type of sample before preparing if outside the above ranges. Dual isotope analysis (C and N) is usually a compromise because the optimal elemental mass for C:N ratio of many materials is higher than ideal. This table gives approximate sizes depending upon type of material. You may also use the following formulas to determine sample size:

formula

  • Sample organization: Samples can be organized and shipped in 96-well culture plates (e.g., Costech “cell wells”, part # 080016 ). Use our file “Sample name form for 15N13C solids” to fill in the names and weights of each sample. Each plate should have a unique name and the sample code should include the plate name and the tray location or cell address (Rows A-H and columns 1-12 are marked on the plates).

If you are not clear about the best way to prepare your samples or are unsure about the optimal sample size(s) to use, please contact us before proceeding. Also if you have special requirements that do not fit within the guidelines provided here, contact us and we can help advise you on the best procedure to use.

GF/F filter material cannot be run on our instruments, please avoid/remove all particles of filter prior to sample encapsulation.