[plateeny]

Hi every body..

As you know the composition of organic matter is( CARBON, H O, N, P, S) , and we calculate organic matter by subtracting moisture and ash from 100 , but some elements  in the ash like( O, N, O) still in the ash and belonge to organic matter.

any correction factor for this?

thanks

[Hunter2]

What is O,N,O? Do you mean O,N,P,S and this belongs to inorganic matter. Because the ash will contain Phosphate and Sulfate, probably also Nitrate. Even Carbonate is not anymore organic.

The organic matter contains compounds from Mr. COHNS Peter. But after combustion all transferred to inorganic.

[Arkcon]

Like Hunter2: said, you application isn't clear, and we can't give you a useful response.  Maybe you can try to be more specific:  what is the orgainic material you're starting with?  Are you sure it contains C, O, H, N, S and P?  Those are important elements in a large bulk of living tissue, but not for all biological products -- sugars, or cellulose won't have proteins or nucleic acids, so that knocks out much of the N, and the S and P, as an example.  How are you charring and roasting the organic material down to ash?  That can affect how we quantify other components.

[discodermolide]

This is usually measured as the sulphate ash.
See http://www.pharmacopeia.cn/v29240/usp29nf24s0_c281.html

[plateeny]

Thanks alot for your answer...

Mostly we estimate the organic matter by charring and roasting the sample down to ash and then subtracting summation of ash and moisture from 100.
as you said most organic matter is protein , sugars ..., and these contais elements like (N, O, P, S) but thsese elements remains in the ash and should be added to the organic matter

[Arkcon]

Still not enough information.  For example, suppose I had a sample of copper plating bath solution -- basically a mixture or copper chloride, sulfuric acid, and proprietary organic modifiers.  I could roast that to dryness, char the remains, and calculate the amount of organic by back calculating the mass of the copper oxide.  (Note: I probably wouldn't do it that way, but this is just an example)  This method would be worthless for an accurate account of say, a food stuff.   But there may be an assay like you described that is adequate for some food stuffs, maybe, like pet food often has a listing on its label % ash, as a general indicator of quality.  You seem to be doing something like the second one, but want much better results, but you're not specific -- what elements do you need to quantitate, how accurately do you need to know them, and what is the matrix these elements are in , so we can help you with problems and pitfalls.