When doing molar nutrient ratios what molar concentration (i.e. mols/g) would you use for organic carbon? Initially I though the molecular weight of glucose since this is the most basic organic carbon source, however I am second guessing now. Any help is appreciated.
Sincerely
Paul Julian
Paul:
I believe that you are correct, glucose would be the standard for organic carbon:
Properties
Chemical formula: C6H12O6
Molar mass: 180.16 g·mol−1
Paul,
If your "organic carbon" is entirely metabolizable carbohydrate, the molecular weight of glucose may suffice as a crude measure but if it contains anything which is either non-metabolizable or other than carbohydrate (such as lipids, proteins and nucleic acids), using molecular weight of glucose will introduce a variable error, extent of which will depend on the relative proportions of various macromolecules in the mixture.
Now to throw a wrench into the question...what molecular weight would you used to convert dissolved inorganic carbon from mass to moles? Would you use carbon or CO2?
Define dissolved "inorganic" carbon!
It's hardly a wrench in the works - it's simple high school chemistry. The answer will obviously depend on the compound -
If your inorganic carbon is reported in mg (or ug)/l C, then use the molecular weight of carbon.
DIC is often converted from mass (ppm) to mol carbon/kg. In that case, the molecular weight of carbon (~12) should be used. Otherwise, it depends on the carbonic acid species which is determined by the pH. Hope this helps
Anyway, I suggest using the Walkley-Black procedure depicted by Nelson and Sommers (Nelson and Sommers, 1982) to find total organic %C in any substance may help you:-
Nelson, D.W., and Sommers, L.E.(1982). Total carbon, organic carbon and organic matter. In A.L. Page (ed), Methods of Soil Analysis, Part 2, Chemical and Microbiological properties. The American society of Agronomy, Soil Science Society of America Wisconsin; 539–580.
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