Quantitative – NCHS

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).
  • 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).
  • For soils processing, contact Greg Cane for further details.

Methodology

Samples are loaded into tin capsules. Soils/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 carousel NC2500 Carlo Erba Instruments 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 and reduce any N2O to N2, 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 quantified with a TCD (Thermal Conductivity Detector).

Analytical precision for N and C is less than 0.1%.

Turnaround Time

  • ≤ 50 samples: 3-4 weeks to process.
  • > 50 samples: 4-5 weeks to process.