Carbon and Nitrogen Isotopes

Requirements

  • Plant leaves should be washed under DI water to remove dust, soil, and/or any extraneous sources of N and C.
  • Plant matter, muds, soils, and any wet samples should be completely dried at 46 °C in a drying oven for several days.
  • All samples should be ground to a fine powder and homogenized before sending. Manual grinding is not possible for samples such as grasses, hairs, feathers, and most plant matter. Use a mill if possible.
  • Samples should be sent in 2 mL low retention or siliconized microcentrifuge tubes (Fisher Scientific Cat # 02-681-321 or NC9492494).
  • Glass fiber filters containing filtered material can be sent wrapped in tin foil, but the %N and %C cannot be determined unless the client has indicated the filtered material weight (typically done with “before” and “after” dry weight of the filter).
  • Roughly 5 mg of plant-based samples and 10 to 100 mg of decarbonated soil/sediment sample is needed for analysis (see requirements for submitting soils/sediments for decarbonation technique).
  • Received samples deemed too coarse (non-homogenized) will be ground via mortar and pestle at the client’s expense on an hourly rate (see Pricing, Billing, and Payment).

Methodology

Please note: Carbon and nitrogen results can be obtained on the same analysis for each sample. It is up to the client to specify if either one or both is required. In rare cases, it is not possible to obtain results for both isotopes on a single analysis. The sample must then be analyzed twice, once for the carbon fraction, and then a second time for the nitrogen. In these cases, the client will be notified prior to analysis, as the cost per sample would be two-fold.

Samples are loaded into tin capsules. Soil/sediment samples require 10 to 100 mg, whereas plant-based samples require anywhere between 2 and 4 mg. Calibration standards and two quality control standards are also weighed. Samples and standards are loaded into a 50-position autosampler carousel connected to a Carlo Erba NC2500 elemental analyzer. Tin capsules are dropped one at a time into a combustion reactor set at 980 °C, and roughly 5 mL of pure oxygen is added to the reaction which flash combusts the aliquot at 1800 °C. Ultra-high purity helium is used as a carrier gas, which transports analytes of CO2, N2, H2O, and SO2 through three columns; i) a copper trap to remove excess oxygen, ii) a magnesium perchlorate trap to remove water, and iii) a GC column to separate the N2 from the CO2 phase. Sample gases are then passed on to a Thermo Fisher Conflo IV linked to Delta V Advantage isotope ratio mass spectrometer for analysis of δ15N and δ13C. Soil sample precision for δ15N is ±0.39‰ and for δ13C is 0.10‰. Plant matter precision for δ15N is ±0.23‰ and for δ13C is 0.08‰.

Turnaround Time

  • ≤ 25 samples: 3-4 weeks to process.
  • > 25 samples: 6-8 weeks to process.