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Mehlich3 ICP (18F1)

Analysis of Mehlich 3 extract using inductively-coupled atomic emission spectroscopy (ICP-AES)

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Total organic carbon - high frequency induction furnace, volumetric (6B2)

This method for total soil OC involves production, purification and measurement of CO2 evolved when soil carbon is ignited in a stream of O2. Because all C compounds are converted to CO2, the C from carbonates, charcoal, undecomposed wood, etc, will be included, as no soil pre-treatment is specified. In the volumetric sub-method 6B2a, concentrated KOH solution is used to absorb the CO2 released. The difference between the original volume of gas in the burette and the volume produced after ignition equals the volume of CO2 evolved from the sample, after correction for gas temperature and pressure. Sub-method 6B2b is similar to Method 6B2a, except the CO2 produced by ignition is measured via infrared / thermal conductivity detection. Both 6B2a and 6B2b use finely-milled air-dry sample, with weights varying with expected C concentrations. Surrogate estimates can be obtained by NIR (method 6B4a) or MIR (method 6B4b) reflectance spectroscopy. The methods specify reporting as %C on an oven-dry (105oC) basis.

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Total soil N – Dumas high-temperature combustion (7A5)

This method utilises automated and/or microprocessor controlled instrumentation, which mostly is able to measure at least total C, N and S in the same sample. Dumas-N dry oxidation includes all forms of soil N, without the need for lengthy pre-treatments, although results can occasionally differ from those expected in soils with high levels of fixed ammonium-N (lower results) and when soils are organically rich (high results, due to incomplete combustion resulting in the formation of methane rather than CO2). Typically, dry, finely-ground sample is subjected to high-temperature combustion (e.g. 950–1,250oC) in a stream of purified O2. An aliquot of the gases produced by combustion is carried by helium gas to a thermal conductivity cell for measurement of any N2 generated, a process typically taking 3–5 min. A heated copper catalyst reduces NOx to N2. The method specifies reporting results as %N on an oven-dry (105oC) basis.
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GI-23

Wet digestion - open system without HF, and final medium HNO3/peroxide.  ICP-AES finish.

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CA-37

Finely divided dry sample.  Dumas combustion.