- Solid samples should be ground to a powder and homogenized before sending.
- If samples are moist or wet, they should be dried at 46 °C in a drying oven for several days.
- Samples such as leaves, grasses, and other plant matter may be difficult to grind.
- Samples should be sent in 2 mL low retention or siliconized microcentrifuge tubes (Fisher Scientific Cat # 02-681-321 or NC9492494).
- Typically, 1 to 2 mg of sample is necessary for analysis.
- 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).
Samples are weighed into silver capsules. Benzoic acid and cellulose standards are also weighed into silver capsules and loaded into a Costech Zero blank autosampler. An isolation valve on the autosampler allows for the capsules to be purged with ultra-high purity helium for ten minutes prior to opening to the reactor assembly and the main helium stream. Pyrolysis of the samples is performed by a Thermo Finnigan TCEA, whereby capsules are dropped one at a time into a glassy carbon reactor set at 1400 °C containing glassy carbon chips. The resulting reaction leads any oxygen to interact with the glassy carbon to produce carbon monoxide and water. These analytes pass through a 1.5 m long 5 Å mol sieve GC column and a chemical water trap before proceeding to a Thermo Fisher Scientific Conflo IV-Delta V isotope ratio mass spectrometer for analysis. Quantitative O values are calculated by analyzing a cellulose standard ten times at variable weight and generating a calibration curve of the standard voltage versus the amount of oxygen weighed. Sample O data is then quantified from this curve knowing the weight of the analyzed sample.
Analytical precision for O is less than 0.1%.
- 6 weeks but subject to change given batch size.