However, inorganic carbon can also be released outside of the carbon cycle through the combustion of materials in manufacturing and the burning of fossil fuels.
By acidifying the sample and flushing with nitrogen or helium the sample removes inorganic carbon, leaving only organic carbon sources for measurement.
The largest sources of inorganic carbon are limestones, dolomites and carbon dioxide, but significant quantities occur in organic deposits of coal, peat, oil and methane clathrates.