Classic Leco TOC:

Accurately weigh 1 gram of whole rock. Acidify in cold HCl for 24hrs (agitate frequently this removes CaCO3), warm the solution to 40 deg Celcius for 24hrs (agitate frequently) this removes dolomite.

Decant onto a paperless filter. Carefully filter with distilled water using a buchan filter (with a slight vacuum) . The residue is 100% carbonate/dolomite free.

The dried paperless filter  can be aalysed directly in a LECO Carbon Analyser. Weight calculated BACK to the original pre-acidification weight.  

You can find this method in many 'classic' papers.  It is the ONLY way to to be 100.000% sure.

So, the remain residue on the paper is out of carbonate?

We don't have a Leco, so if I add H2O2 to this residue the remain is organic matter free???

I only need a fast calculation of it, nothing sofisticated.

You could check this paper 

Thanks Sergio.

I know the procedure of firing samples to 550ºC for 4 hours, but I never was 100% sure about that. Because if we have clay minerals, some of them can give "problems" at temperatures below 550ºC.

But I think this is the faster and best way.

Thanks

H2O2 is the classical technique for removing organic matter is good if you do not need to know the percentage of organic matter in the sample. If you need to know the content of organic matter, the method of ignition at 550oC and 1000oC, for two hours for carbonate carbon and organic matter is relatively reliable.

Another method, as H2O2, is to use bleach to clean with heating at 50 ° C for two hours.

Cheers

Alberto

Carlos- You can also try source rock analyser with TOC option (or widely used name Rock Eval) where you will weigh about 100 mg of powder sample. This way you can both get the Total Organic Carbon (TOC) and also get a rough idea about the type of organic matter in your limestone sample .

(sorry for the english) Maybe the oxidation by dichromate in acid medium (H2SO4) can be suitable.

In a erlenmeyer, first react the carbonate with H2SO4; after make the oxidation of organic matter with the dichromate solution, and so the back titration of the dichromate excess with a standardized iron(II).

Some references:

Sparks. Methods of soil analysis--Part 3, Chemical methods. SSSA, 1996.

Pansu & Gautheyrou. Handbook of Soil Analysis. 2006.

Gregorich & Carter. Soil Sampling and Methods of Analysis. 2007.

Companies like O.I. Analytical provide this kind of services for a reasonable price, so you don't need to own the equipment (TOC analyzer).

If you only want to remove OM, the H2O2 method (slighting heating in a sand bath or in a controlled conditions) could be quick and enough. If not, as Alberto Sanchez indicates, ignition methods it is very useful (that depend if after that you need to work with the remaining sample or not)  

Dear Carlos, the best way for dermining organic matter in rock is utilizing of Rock-Eval 6 instrument, that can determine organic and inorganic carbon seperatly.